import { create } from 'zustand';
import { 
  addEdge, 
  applyNodeChanges,
  applyEdgeChanges,
  type Connection, 
  type Edge, 
  type EdgeChange, 
  type Node, 
  type NodeChange, 
  type OnNodesChange, 
  type OnEdgesChange, 
  type OnConnect,
  getIncomers,
  getOutgoers
} from 'reactflow';

// --- Project / Blueprint types ---
export interface ViewportState {
  x: number;
  y: number;
  zoom: number;
}

export interface BlueprintDocument {
  version: number;
  nodes: Node<NodeData>[];
  edges: Edge[];
  viewport?: ViewportState;
  theme?: 'light' | 'dark';
}

export interface FSItem {
  name: string;
  path: string; // path relative to user root
  type: 'file' | 'folder';
  size?: number | null;
  mtime?: number | null;
  children?: FSItem[];
}

export type NodeStatus = 'idle' | 'loading' | 'success' | 'error';
export type SaveStatus = 'idle' | 'saving' | 'saved' | 'error';

export interface Message {
  id?: string;
  role: 'user' | 'assistant' | 'system';
  content: string;
  sourceTraceId?: string;    // For merged traces: which trace this message came from
  sourceTraceColor?: string; // For merged traces: color of the source trace
}

export interface Trace {
  id: string;
  sourceNodeId: string;
  color: string;
  messages: Message[];
  // Optional merged trace info for visual propagation
  isMerged?: boolean;
  mergedColors?: string[];
  sourceTraceIds?: string[];
}

// Merge strategy types
export type MergeStrategy = 'query_time' | 'response_time' | 'trace_order' | 'grouped' | 'interleaved' | 'summary';

// Merged trace - combines multiple traces with a strategy
export interface MergedTrace {
  id: string;
  sourceNodeId: string;
  sourceTraceIds: string[];  // IDs of traces being merged (in order for trace_order)
  strategy: MergeStrategy;
  colors: string[];          // Colors from source traces (for alternating display)
  messages: Message[];       // Computed merged messages
  summarizedContent?: string; // For summary strategy, stores the LLM-generated summary
}

export interface NodeData {
  label: string;
  model: string;
  temperature: number;
  apiKey?: string;
  systemPrompt: string;
  userPrompt: string;
  mergeStrategy: 'raw' | 'smart';
  enableGoogleSearch?: boolean;
  reasoningEffort: 'low' | 'medium' | 'high';  // For OpenAI reasoning models
  attachedFileIds?: string[]; // IDs of files attached to this node
  disabled?: boolean;  // Greyed out, no interaction
  
  // Traces logic
  traces: Trace[];          // INCOMING Traces
  outgoingTraces: Trace[];  // ALL Outgoing (inherited + self + forks + merged)
  forkedTraces: Trace[];    // Manually created forks from "New" handle
  mergedTraces: MergedTrace[];  // Merged traces from multiple inputs
  activeTraceIds: string[]; 
  
  response: string;    
  status: NodeStatus;
  inputs: number;
  
  // Timestamps for merge logic
  querySentAt?: number;      // Unix timestamp when query was sent
  responseReceivedAt?: number;  // Unix timestamp when response was received
  
  [key: string]: any;
}

export type LLMNode = Node<NodeData>;

// Archived node template (for reuse)
export interface ArchivedNode {
  id: string;
  label: string;
  model: string;
  systemPrompt: string;
  temperature: number;
  reasoningEffort: 'low' | 'medium' | 'high';
  userPrompt?: string;
  response?: string;
  enableGoogleSearch?: boolean;
  attachedFileIds?: string[];
  mergeStrategy?: 'raw' | 'smart';
}

export interface FileMeta {
  id: string;
  name: string;
  size: number;
  mime: string;
  created_at: number;
  provider?: string;
  provider_file_id?: string;
  scopes?: string[];  // "project_path/node_id" composite keys
}

export type UploadFileProvider = 'local' | 'openai' | 'google';

export interface UploadFileOptions {
  provider?: UploadFileProvider;
  purpose?: string;
}

interface FlowState {
  nodes: LLMNode[];
  edges: Edge[];
  selectedNodeId: string | null;
  archivedNodes: ArchivedNode[];  // Stored node templates
  files: FileMeta[];
  uploadingFileIds?: string[];
  theme: 'light' | 'dark';
  projectTree: FSItem[];
  currentBlueprintPath?: string;
  lastViewport?: ViewportState;
  saveStatus: SaveStatus;

  onNodesChange: OnNodesChange;
  onEdgesChange: OnEdgesChange;
  onConnect: OnConnect;
  
  addNode: (node: LLMNode) => void;
  toggleTheme: () => void;
  autoLayout: () => void;
  findNonOverlappingPosition: (baseX: number, baseY: number) => { x: number; y: number };
  updateNodeData: (nodeId: string, data: Partial<NodeData>) => void;
  setSelectedNode: (nodeId: string | null) => void;
  
  getActiveContext: (nodeId: string) => Message[]; 
  
  // Actions
  deleteEdge: (edgeId: string) => void;
  deleteNode: (nodeId: string) => void;
  deleteBranch: (startNodeId?: string, startEdgeId?: string) => void;
  deleteTrace: (startEdgeId: string) => void;
  
  // Archive actions
  toggleNodeDisabled: (nodeId: string) => void;
  archiveNode: (nodeId: string) => void;
  removeFromArchive: (archiveId: string) => void;
  createNodeFromArchive: (archiveId: string, position: { x: number; y: number }) => void;
  
  // Trace disable
  toggleTraceDisabled: (edgeId: string) => void;
  updateEdgeStyles: () => void;

  // Quick Chat helpers
  isTraceComplete: (trace: Trace) => boolean;
  getTraceNodeIds: (trace: Trace) => string[];
  createQuickChatNode: (
    fromNodeId: string, 
    trace: Trace | null, 
    userPrompt: string, 
    response: string, 
    model: string,
    config: Partial<NodeData>
  ) => string; // Returns new node ID

  // Blueprint serialization / persistence
  serializeBlueprint: (viewport?: ViewportState) => BlueprintDocument;
  loadBlueprint: (doc: BlueprintDocument) => ViewportState | undefined;
  saveBlueprintFile: (path: string, viewport?: ViewportState) => Promise<void>;
  readBlueprintFile: (path: string) => Promise<BlueprintDocument>;
  refreshProjectTree: () => Promise<FSItem[]>;
  createProjectFolder: (path: string) => Promise<void>;
  renameProjectItem: (path: string, newName?: string, newPath?: string) => Promise<void>;
  deleteProjectItem: (path: string, isFolder?: boolean) => Promise<void>;
  setCurrentBlueprintPath: (path?: string) => void;
  setLastViewport: (viewport: ViewportState) => void;
  saveCurrentBlueprint: (path?: string, viewport?: ViewportState) => Promise<void>;
  clearBlueprint: () => void;
  loadArchivedNodes: () => Promise<void>;
  saveArchivedNodes: () => Promise<void>;
  refreshFiles: () => Promise<void>;
  uploadFile: (file: File, options?: UploadFileOptions) => Promise<FileMeta>;
  deleteFile: (fileId: string) => Promise<void>;
  setFiles: (files: FileMeta[]) => void;
  setUploading: (ids: string[]) => void;
  addFileScope: (fileId: string, scope: string) => Promise<void>;
  removeFileScope: (fileId: string, scope: string) => Promise<void>;

  // Merge trace functions
  createMergedTrace: (
    nodeId: string,
    sourceTraceIds: string[],
    strategy: MergeStrategy
  ) => string; // Returns merged trace ID
  updateMergedTrace: (
    nodeId: string,
    mergedTraceId: string,
    updates: { sourceTraceIds?: string[]; strategy?: MergeStrategy; summarizedContent?: string }
  ) => void;
  deleteMergedTrace: (nodeId: string, mergedTraceId: string) => void;
  computeMergedMessages: (
    nodeId: string,
    sourceTraceIds: string[],
    strategy: MergeStrategy,
    tracesOverride?: Trace[]
  ) => Message[];

  propagateTraces: () => void;
}

// Hash string to color
const getStableColor = (str: string) => {
  let hash = 0;
  for (let i = 0; i < str.length; i++) {
    hash = str.charCodeAt(i) + ((hash << 5) - hash);
  }
  const hue = Math.abs(hash % 360);
  return `hsl(${hue}, 70%, 60%)`; 
};

import { useAuthStore } from './authStore';

const API_BASE = import.meta.env.VITE_BACKEND_URL || '';
const DEFAULT_USER = 'test';  // Fallback for unauthenticated requests

// Get current username directly from authStore
const getCurrentUser = () => {
  const authState = useAuthStore.getState();
  return authState.user?.username || DEFAULT_USER;
};

// Get auth headers directly from authStore
const getAuthHeaders = (): Record<string, string> => {
  const authState = useAuthStore.getState();
  if (authState.token) {
    return { Authorization: `Bearer ${authState.token}` };
  }
  return {};
};

const jsonFetch = async <T>(url: string, options?: RequestInit): Promise<T> => {
  const authHeaders = getAuthHeaders();
  const res = await fetch(url, {
    ...options,
    headers: {
      ...options?.headers,
      ...authHeaders,
    },
  });
  if (!res.ok) {
    const detail = await res.text();
    throw new Error(detail || `Request failed: ${res.status}`);
  }
  return res.json() as Promise<T>;
};

const useFlowStore = create<FlowState>((set, get) => {

  const validateBlueprint = (doc: any): BlueprintDocument => {
    if (!doc || typeof doc !== 'object') throw new Error('Invalid blueprint: not an object');
    if (typeof doc.version !== 'number') throw new Error('Invalid blueprint: missing version');
    if (!Array.isArray(doc.nodes) || !Array.isArray(doc.edges)) throw new Error('Invalid blueprint: nodes/edges missing');
    return doc as BlueprintDocument;
  };

  return {
  nodes: [],
  edges: [],
  selectedNodeId: null,
  archivedNodes: [],
  files: [],
  uploadingFileIds: [],
  theme: 'light' as const,
  projectTree: [],
  currentBlueprintPath: undefined,
  lastViewport: undefined,
  saveStatus: 'idle',

  toggleTheme: () => {
    const newTheme = get().theme === 'light' ? 'dark' : 'light';
    set({ theme: newTheme });
    // Update document class for global CSS
    if (newTheme === 'dark') {
      document.documentElement.classList.add('dark');
    } else {
      document.documentElement.classList.remove('dark');
    }
  },

  setLastViewport: (viewport: ViewportState) => {
    set({ lastViewport: viewport });
  },

  setFiles: (files: FileMeta[]) => {
    set({ files });
  },
  setUploading: (ids: string[]) => {
    set({ uploadingFileIds: ids });
  },
  findNonOverlappingPosition: (baseX: number, baseY: number) => {
    const { nodes } = get();
    // Estimate larger dimensions to be safe, considering dynamic handles
    const nodeWidth = 300; 
    const nodeHeight = 200; 
    const padding = 20;
    
    let x = baseX;
    let y = baseY;
    let attempts = 0;
    const maxAttempts = 100; // Increase attempts
    
    const isOverlapping = (testX: number, testY: number) => {
      return nodes.some(node => {
        const nodeX = node.position.x;
        const nodeY = node.position.y;
        return !(testX + nodeWidth + padding < nodeX || 
                 testX > nodeX + nodeWidth + padding ||
                 testY + nodeHeight + padding < nodeY || 
                 testY > nodeY + nodeHeight + padding);
      });
    };
    
    // Try positions in a spiral pattern
    while (isOverlapping(x, y) && attempts < maxAttempts) {
      attempts++;
      // Spiral parameters
      const angle = attempts * 0.5; // Slower rotation
      const radius = 50 + attempts * 30; // Faster expansion
      
      x = baseX + Math.cos(angle) * radius;
      y = baseY + Math.sin(angle) * radius;
    }
    
    return { x, y };
  },

  autoLayout: () => {
    const { nodes, edges } = get();
    if (nodes.length === 0) return;
    
    // Find root nodes (no incoming edges)
    const nodesWithIncoming = new Set(edges.map(e => e.target));
    const rootNodes = nodes.filter(n => !nodesWithIncoming.has(n.id));
    
    // BFS to layout nodes in levels
    const nodePositions: Map<string, { x: number; y: number }> = new Map();
    const visited = new Set<string>();
    const queue: { id: string; level: number; index: number }[] = [];
    
    const horizontalSpacing = 350;
    const verticalSpacing = 150;
    
    // Initialize with root nodes
    rootNodes.forEach((node, index) => {
      queue.push({ id: node.id, level: 0, index });
      visited.add(node.id);
    });
    
    // Track nodes per level for vertical positioning
    const nodesPerLevel: Map<number, number> = new Map();
    
    while (queue.length > 0) {
      const { id, level, index } = queue.shift()!;
      
      // Count nodes at this level
      const currentCount = nodesPerLevel.get(level) || 0;
      nodesPerLevel.set(level, currentCount + 1);
      
      // Calculate position
      const x = 100 + level * horizontalSpacing;
      const y = 100 + currentCount * verticalSpacing;
      nodePositions.set(id, { x, y });
      
      // Find child nodes
      const outgoingEdges = edges.filter(e => e.source === id);
      outgoingEdges.forEach((edge, i) => {
        if (!visited.has(edge.target)) {
          visited.add(edge.target);
          queue.push({ id: edge.target, level: level + 1, index: i });
        }
      });
    }
    
    // Handle orphan nodes (not connected to anything)
    let orphanY = 100;
    nodes.forEach(node => {
      if (!nodePositions.has(node.id)) {
        nodePositions.set(node.id, { x: 100, y: orphanY });
        orphanY += verticalSpacing;
      }
    });
    
    // Apply positions
    set({
      nodes: nodes.map(node => ({
        ...node,
        position: nodePositions.get(node.id) || node.position
      }))
    });
  },

  onNodesChange: (changes: NodeChange[]) => {
    // Check if any nodes are being removed
    const hasRemovals = changes.some(c => c.type === 'remove');
    
    set({
      nodes: applyNodeChanges(changes, get().nodes) as LLMNode[],
    });
    
    // If nodes were removed, also clean up related edges and propagate traces
    if (hasRemovals) {
      const removedIds = changes.filter(c => c.type === 'remove').map(c => c.id);
      set({
        edges: get().edges.filter(e => !removedIds.includes(e.source) && !removedIds.includes(e.target))
      });
      get().propagateTraces();
    }
  },
  onEdgesChange: (changes: EdgeChange[]) => {
    set({
      edges: applyEdgeChanges(changes, get().edges),
    });
    get().propagateTraces();
  },
  onConnect: (connection: Connection) => {
    const { nodes, edges } = get();
    const sourceNode = nodes.find(n => n.id === connection.source);
    if (!sourceNode) return;
    
    // Handle prepend connections - only allow from 'new-trace' handle
    // Prepend makes the source node become the NEW HEAD of an existing trace
    if (connection.targetHandle?.startsWith('prepend-')) {
      // Prepend connections MUST come from 'new-trace' handle
      if (connection.sourceHandle !== 'new-trace') {
        console.warn('Prepend connections only allowed from new-trace handle');
        return;
      }
      
      const targetNode = nodes.find(n => n.id === connection.target);
      if (!targetNode) return;
      
      // Get the trace ID from the prepend handle - this is the trace we're joining
      const traceId = connection.targetHandle.replace('prepend-', '').replace('inherited-', '');
      const regularTrace = targetNode.data.outgoingTraces?.find(t => t.id === traceId);
      const mergedTrace = targetNode.data.mergedTraces?.find(m => m.id === traceId);
      const traceColor = regularTrace?.color || (mergedTrace?.colors?.[0]) || getStableColor(traceId);
      
      // Instead of creating a new trace, we JOIN the existing trace
      // The source node (C) becomes the new head of the trace
      // We use the SAME trace ID so it's truly the same trace
      
      // Add this trace as a "forked trace" on the source node so it shows up as an output handle
      // But use the ORIGINAL trace ID (not a new prepend-xxx ID)
      const inheritedTrace: Trace = {
        id: traceId, // Use the SAME trace ID!
        sourceNodeId: sourceNode.id, // C is now the source/head
        color: traceColor,
        messages: [] // Will be populated by propagateTraces
      };
      
      // Add to source node's forkedTraces
      get().updateNodeData(sourceNode.id, {
        forkedTraces: [...(sourceNode.data.forkedTraces || []), inheritedTrace]
      });
      
      // Update target node's forkedTrace to mark it as "prepended"
      // by setting sourceNodeId to the new head (source node)
      const targetForked = targetNode.data.forkedTraces || [];
      const updatedForked = targetForked.map(t => 
        t.id === traceId ? { ...t, sourceNodeId: sourceNode.id } : t
      );
      if (JSON.stringify(updatedForked) !== JSON.stringify(targetForked)) {
        get().updateNodeData(targetNode.id, {
          forkedTraces: updatedForked
        });
      }
      
      // Create the edge using the SAME trace ID
      // This connects C's output to A's prepend input
    set({
        edges: addEdge({ 
          ...connection, 
          sourceHandle: `trace-${traceId}`, // Same trace ID!
          style: { stroke: traceColor, strokeWidth: 2 } 
        }, get().edges),
      });
      
      setTimeout(() => get().propagateTraces(), 0);
      return;
    }
    
    // Helper to trace back the path of a trace by following edges upstream
    const duplicateTracePath = (
      traceId: string, 
      forkAtNodeId: string,
      traceOwnerNodeId?: string,
      pendingEdges: Edge[] = []
    ): { newTraceId: string, newEdges: Edge[], firstNodeId: string } | null => {
      // Trace back from forkAtNodeId to find the origin of this trace
      // We follow incoming edges that match the trace pattern
      
      const pathNodes: string[] = [forkAtNodeId];
      const pathEdges: Edge[] = [];
      let currentNodeId = forkAtNodeId;
      
      // Trace backwards through incoming edges
      while (true) {
        // Find incoming edge to current node that carries THIS trace ID
        const incomingEdge = edges.find(e => 
          e.target === currentNodeId && 
          e.sourceHandle === `trace-${traceId}`
        );
        
        if (!incomingEdge) break; // Reached the start of the trace
        
        pathNodes.unshift(incomingEdge.source);
        pathEdges.unshift(incomingEdge);
        currentNodeId = incomingEdge.source;
      }
      
      // If path only has one node, no upstream to duplicate
      if (pathNodes.length <= 1) return null;
      
      const firstNodeId = pathNodes[0];
      const firstNode = nodes.find(n => n.id === firstNodeId);
      if (!firstNode) return null;
      
      // Create a new trace ID for the duplicated path (guarantee uniqueness even within the same ms)
      const uniq = `${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
      const newTraceId = `fork-${firstNodeId}-${uniq}`;
      const newTraceColor = getStableColor(newTraceId);
      
      // Create new edges for the entire path
      const newEdges: Edge[] = [];
      
      // Track which input handles we're creating for new edges
      const newInputHandles: Map<string, number> = new Map();
      
      for (let i = 0; i < pathEdges.length; i++) {
        const originalEdge = pathEdges[i];
        const fromNodeId = pathNodes[i];
        const toNodeId = pathNodes[i + 1];
        
        // Find the next available input handle for the target node
        // Count existing edges to this node + any new edges we're creating
        const existingEdgesToTarget =
          edges.filter(e => e.target === toNodeId).length +
          pendingEdges.filter(e => e.target === toNodeId).length;
        const newEdgesToTarget = newInputHandles.get(toNodeId) || 0;
        const nextInputIndex = existingEdgesToTarget + newEdgesToTarget;
        newInputHandles.set(toNodeId, newEdgesToTarget + 1);
        
        newEdges.push({
          id: `edge-fork-${uniq}-${i}`,
          source: fromNodeId,
          target: toNodeId,
          sourceHandle: `trace-${newTraceId}`,
          targetHandle: `input-${nextInputIndex}`,
          style: { stroke: newTraceColor, strokeWidth: 2 }
        });
      }
      
      // Find the messages up to the fork point
      const traceOwnerNode = traceOwnerNodeId
        ? nodes.find(n => n.id === traceOwnerNodeId)
        : sourceNode;
      if (!traceOwnerNode) return null;

      const originalTrace = traceOwnerNode.data.outgoingTraces?.find(t => t.id === traceId);
      const messagesUpToFork = originalTrace?.messages || [];
      
      // Add the new trace as a forked trace on the first node
      const newForkTrace: Trace = {
        id: newTraceId,
        sourceNodeId: firstNodeId,
        color: newTraceColor,
        messages: [...messagesUpToFork]
      };
      
      get().updateNodeData(firstNodeId, {
        forkedTraces: [...(firstNode.data.forkedTraces || []), newForkTrace]
      });
      
      return { newTraceId, newEdges, firstNodeId };
    };

    // Helper to duplicate the downstream segment of a trace from a start node to an end node
    const duplicateDownstreamSegment = (
      originalTraceId: string,
      startNodeId: string,
      endNodeId: string,
      newTraceId: string,
      newTraceColor: string,
      newTraceColors: string[]
    ): Edge[] | null => {
      const segmentEdges: Edge[] = [];
      let currentNodeId = startNodeId;
      const visitedEdgeIds = new Set<string>();

      while (currentNodeId !== endNodeId) {
        const nextEdge = edges.find(
          (e) => e.source === currentNodeId && e.sourceHandle === `trace-${originalTraceId}`
        );

        if (!nextEdge || visitedEdgeIds.has(nextEdge.id)) {
          return null;
        }

        segmentEdges.push(nextEdge);
        visitedEdgeIds.add(nextEdge.id);
        currentNodeId = nextEdge.target;
      }

      const newEdges: Edge[] = [];
      const newInputCounts: Map<string, number> = new Map();
      const segmentTimestamp = Date.now();

      segmentEdges.forEach((edge, index) => {
        const targetNodeId = edge.target;
        const existingEdgesToTarget = edges.filter((e) => e.target === targetNodeId).length;
        const additionalEdges = newInputCounts.get(targetNodeId) || 0;
        const nextInputIndex = existingEdgesToTarget + additionalEdges;
        newInputCounts.set(targetNodeId, additionalEdges + 1);

        newEdges.push({
          id: `edge-merged-seg-${segmentTimestamp}-${index}`,
          source: edge.source,
          target: edge.target,
          sourceHandle: `trace-${newTraceId}`,
          targetHandle: `input-${nextInputIndex}`,
          type: 'merged',
          style: { stroke: newTraceColor, strokeWidth: 2 },
          data: { isMerged: true, colors: newTraceColors }
        });
      });

      return newEdges;
    };

    // Helper to duplicate a merged trace by cloning its parent traces and creating a new merged branch
    const duplicateMergedTraceBranch = (
      mergedTrace: Trace,
      forkAtNodeId: string
    ): { newTraceId: string; newEdges: Edge[]; color: string } | null => {
      const mergeNodeId = mergedTrace.sourceNodeId;
      const mergeNode = nodes.find((n) => n.id === mergeNodeId);
      if (!mergeNode) return null;

      const mergedDef =
        mergeNode.data.mergedTraces?.find((m: MergedTrace) => m.id === mergedTrace.id) || null;
      const parentTraceIds = mergedTrace.sourceTraceIds || mergedDef?.sourceTraceIds || [];
      if (parentTraceIds.length === 0) return null;

      let accumulatedEdges: Edge[] = [];
      const newParentTraceIds: string[] = [];
      const parentOverrides: Trace[] = [];

      for (const parentId of parentTraceIds) {
        const originalParentTrace = mergeNode.data.traces?.find((t: Trace) => t.id === parentId);

        if (originalParentTrace?.isMerged && originalParentTrace.sourceTraceIds?.length) {
          const nestedDuplicate = duplicateMergedTraceBranch(originalParentTrace, mergeNodeId);
          if (!nestedDuplicate) {
            return null;
          }
          accumulatedEdges = accumulatedEdges.concat(nestedDuplicate.newEdges);
          newParentTraceIds.push(nestedDuplicate.newTraceId);

          parentOverrides.push({
            ...originalParentTrace,
            id: nestedDuplicate.newTraceId,
          });

          continue;
        }

        const duplicateResult = duplicateTracePath(parentId, mergeNodeId, mergeNodeId, accumulatedEdges);
        if (!duplicateResult) {
          return null;
        }
        accumulatedEdges = accumulatedEdges.concat(duplicateResult.newEdges);
        newParentTraceIds.push(duplicateResult.newTraceId);

        if (originalParentTrace) {
          parentOverrides.push({
            ...originalParentTrace,
            id: duplicateResult.newTraceId,
          });
        }
      }

      const strategy = mergedDef?.strategy || 'trace_order';
      const uniqMerged = `${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
      const newMergedId = `merged-${mergeNodeId}-${uniqMerged}`;
      const newColors =
        parentOverrides.length > 0
          ? parentOverrides.map((t) => t.color).filter((c): c is string => Boolean(c))
          : mergedTrace.mergedColors ?? [];

      const overrideTraces = parentOverrides.length > 0 ? parentOverrides : undefined;
      const mergedMessages = get().computeMergedMessages(
        mergeNodeId,
        newParentTraceIds,
        strategy,
        overrideTraces
      );

      const newMergedDefinition: MergedTrace = {
        id: newMergedId,
        sourceNodeId: mergeNodeId,
        sourceTraceIds: newParentTraceIds,
        strategy,
        colors: newColors.length ? newColors : [mergedTrace.color],
        messages: mergedMessages,
      };

      const existingMerged = mergeNode.data.mergedTraces || [];
      get().updateNodeData(mergeNodeId, {
        mergedTraces: [...existingMerged, newMergedDefinition],
      });

      const newMergedColor = newColors[0] || mergedTrace.color || getStableColor(newMergedId);
      const downstreamEdges = duplicateDownstreamSegment(
        mergedTrace.id,
        mergeNodeId,
        forkAtNodeId,
        newMergedId,
        newMergedColor,
        newColors.length ? newColors : [mergedTrace.color]
      );
      if (!downstreamEdges) return null;

      accumulatedEdges = accumulatedEdges.concat(downstreamEdges);

      return {
        newTraceId: newMergedId,
        newEdges: accumulatedEdges,
        color: newMergedColor,
      };
    };
    
    // Helper to create a simple forked trace (for new-trace handle or first connection)
    const createSimpleForkTrace = () => {
      let originalTraceMessages: Message[] = [];
      
      if (connection.sourceHandle?.startsWith('trace-')) {
        const originalTraceId = connection.sourceHandle.replace('trace-', '');
        const originalTrace = sourceNode.data.outgoingTraces?.find(t => t.id === originalTraceId);
        if (originalTrace) {
          originalTraceMessages = [...originalTrace.messages];
        }
      }
      
      if (originalTraceMessages.length === 0) {
        if (sourceNode.data.userPrompt) {
          originalTraceMessages.push({ id: `${sourceNode.id}-u`, role: 'user', content: sourceNode.data.userPrompt });
        }
        if (sourceNode.data.response) {
          originalTraceMessages.push({ id: `${sourceNode.id}-a`, role: 'assistant', content: sourceNode.data.response });
        }
      }
      
      const newForkId = `fork-${sourceNode.id}-${Date.now()}`;
      const newForkTrace: Trace = {
        id: newForkId,
        sourceNodeId: sourceNode.id,
        color: getStableColor(newForkId),
        messages: originalTraceMessages
      };
      
      get().updateNodeData(sourceNode.id, {
        forkedTraces: [...(sourceNode.data.forkedTraces || []), newForkTrace]
      });
      
      return newForkTrace;
    };
    
    // Check if connecting from "new-trace" handle - always create simple fork
    if (connection.sourceHandle === 'new-trace') {
      const newForkTrace = createSimpleForkTrace();
      
      set({
        edges: addEdge({ 
          ...connection, 
          sourceHandle: `trace-${newForkTrace.id}`,
          style: { stroke: newForkTrace.color, strokeWidth: 2 } 
        }, get().edges),
      });
      
      setTimeout(() => get().propagateTraces(), 0);
      return;
    }
    
    // Check if this trace handle already has a downstream connection
    const existingEdgeFromHandle = edges.find(
      e => e.source === connection.source && e.sourceHandle === connection.sourceHandle
    );
    
    if (existingEdgeFromHandle && connection.sourceHandle?.startsWith('trace-')) {
      const originalTraceId = connection.sourceHandle.replace('trace-', '');
      const traceMeta = sourceNode.data.outgoingTraces?.find((t: Trace) => t.id === originalTraceId);

      if (traceMeta?.isMerged && traceMeta.sourceTraceIds && traceMeta.sourceTraceIds.length > 0) {
        const mergedDuplicate = duplicateMergedTraceBranch(traceMeta, connection.source!);
        if (mergedDuplicate) {
          set({
            edges: [
              ...get().edges,
              ...mergedDuplicate.newEdges,
              {
              id: `edge-${connection.source}-${connection.target}-${Date.now()}`,
              source: connection.source!,
              target: connection.target!,
              sourceHandle: `trace-${mergedDuplicate.newTraceId}`,
              targetHandle: connection.targetHandle,
              type: 'merged',
              style: { stroke: mergedDuplicate.color, strokeWidth: 2 },
              data: { isMerged: true, colors: traceMeta.mergedColors || [] }
              } as Edge
            ],
          });
          
          setTimeout(() => get().propagateTraces(), 0);
          return;
        }
      }

      const duplicateResult = duplicateTracePath(originalTraceId, connection.source!);
      
      if (duplicateResult) {
        const { newTraceId, newEdges } = duplicateResult;
        const newTraceColor = getStableColor(newTraceId);
        
        set({
          edges: [
            ...get().edges,
            ...newEdges,
            {
              id: `edge-${connection.source}-${connection.target}-${Date.now()}`,
              source: connection.source!,
              target: connection.target!,
              sourceHandle: `trace-${newTraceId}`,
              targetHandle: connection.targetHandle,
              style: { stroke: newTraceColor, strokeWidth: 2 }
            } as Edge
          ],
        });
        
        setTimeout(() => get().propagateTraces(), 0);
        return;
      } else {
        const newForkTrace = createSimpleForkTrace();
        
        set({
          edges: addEdge({ 
            ...connection, 
            sourceHandle: `trace-${newForkTrace.id}`,
            style: { stroke: newForkTrace.color, strokeWidth: 2 } 
          }, get().edges),
        });
        
        setTimeout(() => get().propagateTraces(), 0);
        return;
      }
    }
    
    // Normal connection - no existing edge from this handle
    set({
      edges: addEdge({ 
        ...connection, 
        style: { stroke: '#888', strokeWidth: 2 } 
      }, get().edges),
    });
    setTimeout(() => get().propagateTraces(), 0);
  },

  addNode: (node: LLMNode) => {
    set((state) => ({ nodes: [...state.nodes, node] }));
    setTimeout(() => get().propagateTraces(), 0);
  },

  updateNodeData: (nodeId: string, data: Partial<NodeData>) => {
    set((state) => ({
      nodes: state.nodes.map((node) => {
        if (node.id === nodeId) {
          return { ...node, data: { ...node.data, ...data } };
        }
        return node;
      }),
    }));
    
    // Only propagate traces when response changes (affects downstream context)
    // Do NOT propagate on userPrompt changes to avoid resetting activeTraceIds during typing
    if (data.response !== undefined) {
      get().propagateTraces();
    }
  },

  setSelectedNode: (nodeId: string | null) => {
    set({ selectedNodeId: nodeId });
  },

  getActiveContext: (nodeId: string) => {
    const node = get().nodes.find(n => n.id === nodeId);
    if (!node) return [];

    const activeIds = node.data.activeTraceIds || [];
    if (activeIds.length === 0) return [];
    
    // Collect all traces by ID to avoid duplicates
    const tracesById = new Map<string, Trace>();
    
    // Add incoming traces
    (node.data.traces || []).forEach((t: Trace) => {
      if (activeIds.includes(t.id)) {
        tracesById.set(t.id, t);
      }
    });
    
    // Add outgoing traces (only if not already in incoming)
    (node.data.outgoingTraces || []).forEach((t: Trace) => {
      if (activeIds.includes(t.id) && !tracesById.has(t.id)) {
        tracesById.set(t.id, t);
      }
    });
    
    // Collect messages from selected traces
    const contextMessages: Message[] = [];
    const nodePrefix = `${nodeId}-`;
    
    tracesById.forEach((t: Trace) => {
      // For traces originated by this node, filter out this node's own messages
      const isOriginated = t.id === `trace-${nodeId}` || 
                          t.id.startsWith('fork-') || 
                          (t.id.startsWith('prepend-') && t.id.includes(`-from-${nodeId}`));
      
      if (isOriginated) {
        // Only include prepended upstream messages
        const prependedMessages = t.messages.filter(m => !m.id?.startsWith(nodePrefix));
        contextMessages.push(...prependedMessages);
      } else {
        // Include all messages for incoming traces
        contextMessages.push(...t.messages);
      }
    });
    
    // Check merged traces
    const activeMerged = (node.data.mergedTraces || []).filter((m: MergedTrace) => 
      activeIds.includes(m.id)
    );
    activeMerged.forEach((m: MergedTrace) => {
      contextMessages.push(...m.messages);
    });
    
    return contextMessages;
  },

  deleteEdge: (edgeId: string) => {
    set({
      edges: get().edges.filter(e => e.id !== edgeId)
    });
    get().propagateTraces();
  },

  deleteNode: (nodeId: string) => {
    set({
      nodes: get().nodes.filter(n => n.id !== nodeId),
      edges: get().edges.filter(e => e.source !== nodeId && e.target !== nodeId)
    });
    get().propagateTraces();
  },

  deleteBranch: (startNodeId?: string, startEdgeId?: string) => {
    const { edges, nodes } = get();
    // We ONLY delete edges, NOT nodes.
    const edgesToDelete = new Set<string>();

    // Helper to traverse downstream EDGES based on Trace Dependency
    const traverse = (currentEdge: Edge) => {
      if (edgesToDelete.has(currentEdge.id)) return;
      edgesToDelete.add(currentEdge.id);
      
      const targetNodeId = currentEdge.target;
      // Identify the trace ID carried by this edge
      const traceId = currentEdge.sourceHandle?.replace('trace-', '');
      if (!traceId) return; 
      
      // Look for outgoing edges from the target node that carry the EVOLUTION of this trace.
      // Our logic generates next trace ID as: `${traceId}_${targetNodeId}`
      const expectedNextTraceId = `${traceId}_${targetNodeId}`;
      
      const outgoing = edges.filter(e => e.source === targetNodeId);
      outgoing.forEach(nextEdge => {
        // If the outgoing edge carries the evolved trace, delete it too
        if (nextEdge.sourceHandle === `trace-${expectedNextTraceId}`) {
          traverse(nextEdge);
        }
      });
    };

    if (startNodeId) {
      // If deleting a node, we delete ALL outgoing edges recursively.
      // Because all traces passing through this node are broken.
      // But we can't use `traverse` directly because we don't have a single start edge.
      // We just start traverse on ALL outgoing edges of this node.
      const initialOutgoing = edges.filter(e => e.source === startNodeId);
      initialOutgoing.forEach(e => traverse(e));
      
      // Also delete incoming to this node
      const incomingToNode = edges.filter(e => e.target === startNodeId);
      incomingToNode.forEach(e => edgesToDelete.add(e.id));
      
      set({
        nodes: nodes.filter(n => n.id !== startNodeId),
        edges: edges.filter(e => !edgesToDelete.has(e.id))
      });
    } else if (startEdgeId) {
      const startEdge = edges.find(e => e.id === startEdgeId);
      if (startEdge) {
        traverse(startEdge);
      }
      
      set({
        edges: edges.filter(e => !edgesToDelete.has(e.id))
      });
    }

    get().propagateTraces();
  },

  deleteTrace: (startEdgeId: string) => {
    const { edges, nodes } = get();
    // Delete edges along the trace AND orphaned nodes (nodes with no remaining connections)
    const edgesToDelete = new Set<string>();
    const nodesInTrace = new Set<string>();

    // Helper to traverse downstream EDGES based on Trace Dependency
    const traverse = (currentEdge: Edge) => {
      if (edgesToDelete.has(currentEdge.id)) return;
      edgesToDelete.add(currentEdge.id);
      
      const targetNodeId = currentEdge.target;
      nodesInTrace.add(targetNodeId);
      
      // Identify the trace ID carried by this edge
      const traceId = currentEdge.sourceHandle?.replace('trace-', '');
      if (!traceId) return; 
      
      // Look for outgoing edges from the target node that carry the EVOLUTION of this trace.
      const expectedNextTraceId = `${traceId}_${targetNodeId}`;
      
      const outgoing = edges.filter(e => e.source === targetNodeId);
      outgoing.forEach(nextEdge => {
        if (nextEdge.sourceHandle === `trace-${expectedNextTraceId}`) {
          traverse(nextEdge);
        }
      });
    };

    // Also traverse backwards to find upstream nodes
    const traverseBackward = (currentEdge: Edge) => {
      if (edgesToDelete.has(currentEdge.id)) return;
      edgesToDelete.add(currentEdge.id);
      
      const sourceNodeId = currentEdge.source;
      nodesInTrace.add(sourceNodeId);
      
      // Find the incoming edge to the source node that is part of the same trace
      const traceId = currentEdge.sourceHandle?.replace('trace-', '');
      if (!traceId) return;
      
      // Find the parent trace ID by removing the last _nodeId suffix
      const lastUnderscore = traceId.lastIndexOf('_');
      if (lastUnderscore > 0) {
        const parentTraceId = traceId.substring(0, lastUnderscore);
        const incoming = edges.filter(e => e.target === sourceNodeId);
        incoming.forEach(prevEdge => {
          if (prevEdge.sourceHandle === `trace-${parentTraceId}`) {
            traverseBackward(prevEdge);
          }
        });
      }
    };

    const startEdge = edges.find(e => e.id === startEdgeId);
    if (startEdge) {
      // Traverse forward
      traverse(startEdge);
      // Traverse backward
      traverseBackward(startEdge);
    }
    
    // Filter remaining edges after deletion
    const remainingEdges = edges.filter(e => !edgesToDelete.has(e.id));
    
    // Find nodes that become orphaned (no connections at all after edge deletion)
    const nodesToDelete = new Set<string>();
    nodesInTrace.forEach(nodeId => {
      const hasRemainingEdges = remainingEdges.some(
        e => e.source === nodeId || e.target === nodeId
      );
      if (!hasRemainingEdges) {
        nodesToDelete.add(nodeId);
      }
    });
    
    set({
      nodes: nodes.filter(n => !nodesToDelete.has(n.id)),
      edges: remainingEdges
    });

    get().propagateTraces();
  },

  toggleNodeDisabled: (nodeId: string) => {
    const node = get().nodes.find(n => n.id === nodeId);
    if (node) {
      const newDisabled = !node.data.disabled;
      // Update node data AND draggable property
      set(state => ({
        nodes: state.nodes.map(n => {
          if (n.id === nodeId) {
            return {
              ...n,
              draggable: !newDisabled,  // Disable dragging when node is disabled
              selectable: !newDisabled, // Disable selection when node is disabled
              data: { ...n.data, disabled: newDisabled }
            };
          }
          return n;
        })
      }));
      // Update edge styles to reflect disabled state
      setTimeout(() => get().updateEdgeStyles(), 0);
    }
  },

  archiveNode: (nodeId: string) => {
    const node = get().nodes.find(n => n.id === nodeId);
    if (!node) return;
    
    const archived: ArchivedNode = {
      id: `archive_${Date.now()}`,
      label: node.data.label,
      model: node.data.model,
      systemPrompt: node.data.systemPrompt,
      temperature: node.data.temperature,
      reasoningEffort: node.data.reasoningEffort || 'medium',
      userPrompt: node.data.userPrompt,
      response: node.data.response,
      enableGoogleSearch: node.data.enableGoogleSearch,
      mergeStrategy: node.data.mergeStrategy,
      attachedFileIds: node.data.attachedFileIds || []
    };
    
    set(state => ({
      archivedNodes: [...state.archivedNodes, archived]
    }));
    setTimeout(() => get().saveArchivedNodes().catch(() => {}), 0);
  },

  removeFromArchive: (archiveId: string) => {
    set(state => ({
      archivedNodes: state.archivedNodes.filter(a => a.id !== archiveId)
    }));
    setTimeout(() => get().saveArchivedNodes().catch(() => {}), 0);
  },

  createNodeFromArchive: (archiveId: string, position: { x: number; y: number }) => {
    const archived = get().archivedNodes.find(a => a.id === archiveId);
    if (!archived) return;
    
    const newNode: LLMNode = {
      id: `node_${Date.now()}`,
      type: 'llmNode',
      position,
      data: {
        label: archived.label,
        model: archived.model,
        temperature: archived.temperature,
        systemPrompt: archived.systemPrompt,
        userPrompt: archived.userPrompt || '',
        reasoningEffort: archived.reasoningEffort,
        enableGoogleSearch: archived.enableGoogleSearch,
        mergeStrategy: archived.mergeStrategy || 'smart',
        traces: [],
        outgoingTraces: [],
        forkedTraces: [],
        mergedTraces: [],
        activeTraceIds: [],
        attachedFileIds: archived.attachedFileIds || [],
        response: archived.response || '',
        status: 'idle',
        inputs: 1
      }
    };
    
    get().addNode(newNode);
  },

  toggleTraceDisabled: (edgeId: string) => {
    const { edges, nodes } = get();
    const edge = edges.find(e => e.id === edgeId);
    if (!edge) return;
    
    // Find all nodes connected through this trace (BIDIRECTIONAL)
    const nodesInTrace = new Set<string>();
    const visitedEdges = new Set<string>();
    
    // Traverse downstream (source -> target direction)
    const traverseDownstream = (currentNodeId: string) => {
      nodesInTrace.add(currentNodeId);
      
      const outgoing = edges.filter(e => e.source === currentNodeId);
      outgoing.forEach(nextEdge => {
        if (visitedEdges.has(nextEdge.id)) return;
        visitedEdges.add(nextEdge.id);
        traverseDownstream(nextEdge.target);
      });
    };
    
    // Traverse upstream (target -> source direction)
    const traverseUpstream = (currentNodeId: string) => {
      nodesInTrace.add(currentNodeId);
      
      const incoming = edges.filter(e => e.target === currentNodeId);
      incoming.forEach(prevEdge => {
        if (visitedEdges.has(prevEdge.id)) return;
        visitedEdges.add(prevEdge.id);
        traverseUpstream(prevEdge.source);
      });
    };
    
    // Start bidirectional traversal from clicked edge
    visitedEdges.add(edge.id);
    
    // Go upstream from source (including source itself)
    traverseUpstream(edge.source);
    
    // Go downstream from target (including target itself)  
    traverseDownstream(edge.target);
    
    // Check if any node in this trace is disabled
    const anyDisabled = Array.from(nodesInTrace).some(
      nodeId => nodes.find(n => n.id === nodeId)?.data.disabled
    );
    
    // Toggle: if any disabled -> enable all, else disable all
    const newDisabledState = !anyDisabled;
    
    set(state => ({
      nodes: state.nodes.map(node => {
        if (nodesInTrace.has(node.id)) {
          return { 
            ...node, 
            draggable: !newDisabledState,
            selectable: !newDisabledState,
            data: { ...node.data, disabled: newDisabledState } 
          };
        }
        return node;
      })
    }));
    
    // Update edge styles
    get().updateEdgeStyles();
  },

  updateEdgeStyles: () => {
    const { nodes, edges } = get();
    
    const updatedEdges = edges.map(edge => {
      const sourceNode = nodes.find(n => n.id === edge.source);
      const targetNode = nodes.find(n => n.id === edge.target);
      
      const isDisabled = sourceNode?.data.disabled || targetNode?.data.disabled;
      
      return {
        ...edge,
        style: {
          ...edge.style,
          opacity: isDisabled ? 0.3 : 1,
          strokeDasharray: isDisabled ? '5,5' : undefined
        }
      };
    });
    
    set({ edges: updatedEdges });
  },

  // Check if all nodes in trace path have complete Q&A
  isTraceComplete: (trace: Trace) => {
    // A trace is complete if all nodes in the path have complete Q&A pairs
    const messages = trace.messages;
    
    if (messages.length === 0) {
      // Empty trace - check if the source node has content
      const { nodes } = get();
      const sourceNode = nodes.find(n => n.id === trace.sourceNodeId);
      if (sourceNode) {
        return !!sourceNode.data.userPrompt && !!sourceNode.data.response;
      }
      return true; // No source node, assume complete
    }
    
    // Extract node IDs from message IDs (format: nodeId-user or nodeId-assistant)
    // Group messages by node and check each node has both user and assistant
    const nodeMessages = new Map<string, { hasUser: boolean; hasAssistant: boolean }>();
    
    for (const msg of messages) {
      if (!msg.id) continue;
      
      // Parse nodeId from message ID (format: nodeId-user or nodeId-assistant)
      const parts = msg.id.split('-');
      if (parts.length < 2) continue;
      
      // The nodeId is everything except the last part (user/assistant)
      const lastPart = parts[parts.length - 1];
      const nodeId = lastPart === 'user' || lastPart === 'assistant' 
        ? parts.slice(0, -1).join('-')
        : msg.id; // Fallback: use whole ID if format doesn't match
      
      if (!nodeMessages.has(nodeId)) {
        nodeMessages.set(nodeId, { hasUser: false, hasAssistant: false });
      }
      
      const nodeData = nodeMessages.get(nodeId)!;
      if (msg.role === 'user') nodeData.hasUser = true;
      if (msg.role === 'assistant') nodeData.hasAssistant = true;
    }
    
    // Check that ALL nodes in the trace have both user and assistant messages
    for (const [nodeId, data] of nodeMessages) {
      if (!data.hasUser || !data.hasAssistant) {
        return false; // This node is incomplete
      }
    }
    
    // Must have at least one complete node
    return nodeMessages.size > 0;
  },

  // Get all node IDs in trace path
  getTraceNodeIds: (trace: Trace) => {
    const traceId = trace.id;
    const parts = traceId.replace('trace-', '').split('_');
    return parts.filter(p => p.startsWith('node') || get().nodes.some(n => n.id === p));
  },

  // Create a new node for quick chat, with proper connection
  createQuickChatNode: (
    fromNodeId: string,
    trace: Trace | null,
    userPrompt: string,
    response: string,
    model: string,
    config: Partial<NodeData>
  ) => {
    const { nodes, edges, addNode, updateNodeData } = get();
    const fromNode = nodes.find(n => n.id === fromNodeId);
    
    if (!fromNode) return '';

    // Check if current node is empty (no response) -> overwrite it
    const isCurrentNodeEmpty = !fromNode.data.response;
    
    if (isCurrentNodeEmpty) {
      // Overwrite current node
      updateNodeData(fromNodeId, {
        userPrompt,
        response,
        model,
        status: 'success',
        querySentAt: Date.now(),
        responseReceivedAt: Date.now(),
        ...config
      });
      return fromNodeId;
    }
    
    // Create new node to the right
    // Use findNonOverlappingPosition to avoid collision, starting from the ideal position
    const idealX = fromNode.position.x + 300;
    const idealY = fromNode.position.y;
    
    // Check if ideal position overlaps
    const { findNonOverlappingPosition } = get();
    const newPos = findNonOverlappingPosition(idealX, idealY);
    
    const newNodeId = `node_${Date.now()}`;
    const newNode: LLMNode = {
      id: newNodeId,
      type: 'llmNode',
      position: newPos,
      data: {
        label: 'Quick Chat',
        model,
        temperature: config.temperature || 0.7,
        systemPrompt: '',
        userPrompt,
        mergeStrategy: 'smart',
        reasoningEffort: config.reasoningEffort || 'medium',
        enableGoogleSearch: config.enableGoogleSearch,
        traces: [],
        outgoingTraces: [],
        forkedTraces: [],
        mergedTraces: [],
        activeTraceIds: [],
        attachedFileIds: [],
        response,
        status: 'success',
        inputs: 1,
        querySentAt: Date.now(),
        responseReceivedAt: Date.now(),
        ...config
      }
    };
    
    addNode(newNode);
    
    // Connect from the source node using new-trace handle (creates a fork)
    setTimeout(() => {
      const store = useFlowStore.getState();
      store.onConnect({
        source: fromNodeId,
        sourceHandle: 'new-trace',
        target: newNodeId,
        targetHandle: 'input-0'
      });
    }, 50);
    
    return newNodeId;
  },

  // -------- Blueprint serialization / persistence --------
  setCurrentBlueprintPath: (path?: string) => {
    set({ currentBlueprintPath: path });
  },

  serializeBlueprint: (viewport?: ViewportState): BlueprintDocument => {
    return {
      version: 1,
      nodes: get().nodes,
      edges: get().edges,
      viewport: viewport || get().lastViewport,
      theme: get().theme,
    };
  },

  loadBlueprint: (doc: BlueprintDocument): ViewportState | undefined => {
    set({
      nodes: (doc.nodes || []) as LLMNode[],
      edges: (doc.edges || []) as Edge[],
      theme: doc.theme || get().theme,
      selectedNodeId: null,
      lastViewport: doc.viewport || get().lastViewport,
    });
    // Recompute traces after loading
    setTimeout(() => get().propagateTraces(), 0);
    return doc.viewport;
  },

  saveBlueprintFile: async (path: string, viewport?: ViewportState) => {
    const payload = get().serializeBlueprint(viewport);
    await jsonFetch(`${API_BASE}/api/projects/save_blueprint`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        user: getCurrentUser(),
        path,
        content: payload,
      }),
    });
    set({ currentBlueprintPath: path, lastViewport: payload.viewport });
    await get().refreshProjectTree();
  },

  readBlueprintFile: async (path: string): Promise<BlueprintDocument> => {
    const res = await jsonFetch<{ content: BlueprintDocument }>(
      `${API_BASE}/api/projects/file?user=${encodeURIComponent(getCurrentUser())}&path=${encodeURIComponent(path)}`
    );
    return validateBlueprint(res.content);
  },

  refreshProjectTree: async () => {
    const tree = await jsonFetch<FSItem[]>(
      `${API_BASE}/api/projects/tree?user=${encodeURIComponent(getCurrentUser())}`
    );
    set({ projectTree: tree });
    return tree;
  },

  createProjectFolder: async (path: string) => {
    await jsonFetch(`${API_BASE}/api/projects/create_folder`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ user: DEFAULT_USER, path }),
    });
    await get().refreshProjectTree();
  },

  renameProjectItem: async (path: string, newName?: string, newPath?: string) => {
    if (!newName && !newPath) {
      throw new Error('newName or newPath is required');
    }
    await jsonFetch(`${API_BASE}/api/projects/rename`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ user: DEFAULT_USER, path, new_name: newName, new_path: newPath }),
    });
    await get().refreshProjectTree();
  },

  deleteProjectItem: async (path: string, isFolder = false) => {
    await jsonFetch(`${API_BASE}/api/projects/delete`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ user: DEFAULT_USER, path, is_folder: isFolder }),
    });
    await get().refreshProjectTree();
  },

  saveCurrentBlueprint: async (path?: string, viewport?: ViewportState) => {
    const targetPath = path || get().currentBlueprintPath;
    if (!targetPath) {
      throw new Error('No blueprint path. Please provide a file name.');
    }
    set({ saveStatus: 'saving' });
    try {
      await get().saveBlueprintFile(targetPath, viewport);
      set({ saveStatus: 'saved', currentBlueprintPath: targetPath });
    } catch (e) {
      console.error(e);
      set({ saveStatus: 'error' });
      throw e;
    }
  },

  clearBlueprint: () => {
    set({
      nodes: [],
      edges: [],
      selectedNodeId: null,
      currentBlueprintPath: undefined,
      lastViewport: undefined,
      saveStatus: 'idle',
    });
  },

  loadArchivedNodes: async () => {
    const res = await jsonFetch<{ archived: ArchivedNode[] }>(
      `${API_BASE}/api/projects/archived?user=${encodeURIComponent(getCurrentUser())}`
    );
    set({ archivedNodes: res.archived || [] });
  },

  saveArchivedNodes: async () => {
    const payload = { user: DEFAULT_USER, archived: get().archivedNodes };
    await jsonFetch(`${API_BASE}/api/projects/archived`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(payload),
    });
  },

  // Files management
  refreshFiles: async () => {
    const res = await jsonFetch<{ files: FileMeta[] }>(
      `${API_BASE}/api/files?user=${encodeURIComponent(getCurrentUser())}`
    );
    set({ files: res.files || [] });
  },

  uploadFile: async (file: File, options?: UploadFileOptions) => {
    const provider = options?.provider ?? 'local';
    const purpose = options?.purpose;
    const tempId = `${file.name}-${Date.now()}`;
    const prev = get().uploadingFileIds || [];
    set({ uploadingFileIds: [...prev, tempId] });
    const form = new FormData();
    form.append('file', file);
    form.append('provider', provider);
    if (purpose) {
      form.append('purpose', purpose);
    }
    try {
      const res = await fetch(`${API_BASE}/api/files/upload?user=${encodeURIComponent(getCurrentUser())}`, {
        method: 'POST',
        body: form,
      });
      if (!res.ok) {
        throw new Error(await res.text());
      }
      const data = await res.json();
      if (!data.file) {
        throw new Error('Upload succeeded but no file info returned');
      }
      await get().refreshFiles();
      return data.file as FileMeta;
    } finally {
      set({ uploadingFileIds: (get().uploadingFileIds || []).filter(id => id !== tempId) });
    }
  },

  deleteFile: async (fileId: string) => {
    const res = await fetch(`${API_BASE}/api/files/delete?user=${encodeURIComponent(getCurrentUser())}&file_id=${encodeURIComponent(fileId)}`, {
      method: 'POST',
    });
    if (!res.ok) {
      throw new Error(await res.text());
    }
    await get().refreshFiles();
  },

  addFileScope: async (fileId: string, scope: string) => {
    const res = await fetch(`${API_BASE}/api/files/add_scope`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ user: DEFAULT_USER, file_id: fileId, scope }),
    });
    if (!res.ok) {
      throw new Error(await res.text());
    }
    await get().refreshFiles();
  },

  removeFileScope: async (fileId: string, scope: string) => {
    const res = await fetch(`${API_BASE}/api/files/remove_scope`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ user: DEFAULT_USER, file_id: fileId, scope }),
    });
    if (!res.ok) {
      throw new Error(await res.text());
    }
    await get().refreshFiles();
  },

  // --------------------------------------------------------

  // Compute merged messages based on strategy
  // Optional tracesOverride parameter to use latest traces during propagation
  computeMergedMessages: (nodeId: string, sourceTraceIds: string[], strategy: MergeStrategy, tracesOverride?: Trace[]): Message[] => {
    const { nodes } = get();
    const node = nodes.find(n => n.id === nodeId);
    if (!node) return [];

    // Use override traces if provided (for propagation), otherwise use node's stored traces
    const availableTraces = tracesOverride || node.data.traces || [];
    
    // Get the source traces
    const sourceTraces = sourceTraceIds
      .map(id => availableTraces.find((t: Trace) => t.id === id))
      .filter((t): t is Trace => t !== undefined);

    if (sourceTraces.length === 0) return [];

    // Helper to add source trace info to a message
    const tagMessage = (msg: Message, trace: Trace): Message => ({
      ...msg,
      sourceTraceId: trace.id,
      sourceTraceColor: trace.color
    });

    // Helper to get timestamp for a message based on node
    const getMessageTimestamp = (msg: Message, type: 'query' | 'response'): number => {
      // Extract node ID from message ID (format: nodeId-user or nodeId-assistant)
      const msgNodeId = msg.id?.split('-')[0];
      if (!msgNodeId) return 0;
      
      const msgNode = nodes.find(n => n.id === msgNodeId);
      if (!msgNode) return 0;
      
      if (type === 'query') {
        return msgNode.data.querySentAt || 0;
      } else {
        return msgNode.data.responseReceivedAt || 0;
      }
    };

    // Helper to get all messages with their timestamps and trace info
    const getAllMessagesWithTime = () => {
      const allMessages: { msg: Message; queryTime: number; responseTime: number; trace: Trace }[] = [];
      
      sourceTraces.forEach((trace) => {
        trace.messages.forEach(msg => {
          allMessages.push({
            msg: tagMessage(msg, trace),
            queryTime: getMessageTimestamp(msg, 'query'),
            responseTime: getMessageTimestamp(msg, 'response'),
            trace
          });
        });
      });
      
      return allMessages;
    };

    switch (strategy) {
      case 'query_time': {
        // Sort by query time, keeping Q-A pairs together
        const pairs: { user: Message | null; assistant: Message | null; time: number; trace: Trace }[] = [];
        
        sourceTraces.forEach(trace => {
          for (let i = 0; i < trace.messages.length; i += 2) {
            const user = trace.messages[i];
            const assistant = trace.messages[i + 1] || null;
            const time = getMessageTimestamp(user, 'query');
            pairs.push({ 
              user: user ? tagMessage(user, trace) : null, 
              assistant: assistant ? tagMessage(assistant, trace) : null, 
              time,
              trace
            });
          }
        });
        
        pairs.sort((a, b) => a.time - b.time);
        
        const result: Message[] = [];
        pairs.forEach(pair => {
          if (pair.user) result.push(pair.user);
          if (pair.assistant) result.push(pair.assistant);
        });
        return result;
      }

      case 'response_time': {
        // Sort by response time, keeping Q-A pairs together
        const pairs: { user: Message | null; assistant: Message | null; time: number; trace: Trace }[] = [];
        
        sourceTraces.forEach(trace => {
          for (let i = 0; i < trace.messages.length; i += 2) {
            const user = trace.messages[i];
            const assistant = trace.messages[i + 1] || null;
            const time = getMessageTimestamp(assistant || user, 'response');
            pairs.push({ 
              user: user ? tagMessage(user, trace) : null, 
              assistant: assistant ? tagMessage(assistant, trace) : null, 
              time,
              trace
            });
          }
        });
        
        pairs.sort((a, b) => a.time - b.time);
        
        const result: Message[] = [];
        pairs.forEach(pair => {
          if (pair.user) result.push(pair.user);
          if (pair.assistant) result.push(pair.assistant);
        });
        return result;
      }

      case 'trace_order': {
        // Simply concatenate in the order of sourceTraceIds
        const result: Message[] = [];
        sourceTraces.forEach(trace => {
          trace.messages.forEach(msg => {
            result.push(tagMessage(msg, trace));
          });
        });
        return result;
      }

      case 'grouped': {
        // Same as trace_order but more explicitly grouped
        const result: Message[] = [];
        sourceTraces.forEach(trace => {
          trace.messages.forEach(msg => {
            result.push(tagMessage(msg, trace));
          });
        });
        return result;
      }

      case 'interleaved': {
        // True interleaving - sort ALL messages by their actual time
        const allMessages = getAllMessagesWithTime();
        
        // Sort by the earlier of query/response time for each message
        allMessages.sort((a, b) => {
          const aTime = a.msg.role === 'user' ? a.queryTime : a.responseTime;
          const bTime = b.msg.role === 'user' ? b.queryTime : b.responseTime;
          return aTime - bTime;
        });
        
        return allMessages.map(m => m.msg);
      }

      case 'summary': {
        // For summary, we return all messages in trace order with source tags
        // The actual summarization is done asynchronously and stored in summarizedContent
        const result: Message[] = [];
        sourceTraces.forEach(trace => {
          trace.messages.forEach(msg => {
            result.push(tagMessage(msg, trace));
          });
        });
        return result;
      }

      default:
        return [];
    }
  },

  // Create a new merged trace
  createMergedTrace: (nodeId: string, sourceTraceIds: string[], strategy: MergeStrategy): string => {
    const { nodes, updateNodeData, computeMergedMessages } = get();
    const node = nodes.find(n => n.id === nodeId);
    if (!node) return '';

    // Get colors from source traces (preserve multi-colors for merged parents)
    const colors = sourceTraceIds.flatMap(id => {
      const t = node.data.traces.find((tr: Trace) => tr.id === id);
      if (!t) return [];
      if (t.mergedColors && t.mergedColors.length > 0) return t.mergedColors;
      return t.color ? [t.color] : [];
    });

    // Compute merged messages
    const messages = computeMergedMessages(nodeId, sourceTraceIds, strategy);

    const mergedTraceId = `merged-${nodeId}-${Date.now()}`;
    
    const mergedTrace: MergedTrace = {
      id: mergedTraceId,
      sourceNodeId: nodeId,
      sourceTraceIds,
      strategy,
      colors,
      messages
    };

    const existingMerged = node.data.mergedTraces || [];
    updateNodeData(nodeId, {
      mergedTraces: [...existingMerged, mergedTrace]
    });

    // Trigger trace propagation to update outgoing traces
    setTimeout(() => {
      get().propagateTraces();
    }, 50);

    return mergedTraceId;
  },

  // Update an existing merged trace
  updateMergedTrace: (nodeId: string, mergedTraceId: string, updates: { sourceTraceIds?: string[]; strategy?: MergeStrategy; summarizedContent?: string }) => {
    const { nodes, updateNodeData, computeMergedMessages } = get();
    const node = nodes.find(n => n.id === nodeId);
    if (!node) return;

    const existingMerged = node.data.mergedTraces || [];
    const mergedIndex = existingMerged.findIndex((m: MergedTrace) => m.id === mergedTraceId);
    if (mergedIndex === -1) return;

    const current = existingMerged[mergedIndex];
    const newSourceTraceIds = updates.sourceTraceIds || current.sourceTraceIds;
    const newStrategy = updates.strategy || current.strategy;

    // Recompute colors if source traces changed (preserve multi-colors)
    let newColors = current.colors;
    if (updates.sourceTraceIds) {
      newColors = updates.sourceTraceIds.flatMap(id => {
        const t = node.data.traces.find((tr: Trace) => tr.id === id);
        if (!t) return [];
        if (t.mergedColors && t.mergedColors.length > 0) return t.mergedColors;
        return t.color ? [t.color] : [];
      });
    }

    // Recompute messages if source or strategy changed
    let newMessages = current.messages;
    if (updates.sourceTraceIds || updates.strategy) {
      newMessages = computeMergedMessages(nodeId, newSourceTraceIds, newStrategy);
    }

    const updatedMerged = [...existingMerged];
    updatedMerged[mergedIndex] = {
      ...current,
      sourceTraceIds: newSourceTraceIds,
      strategy: newStrategy,
      colors: newColors,
      messages: newMessages,
      summarizedContent: updates.summarizedContent !== undefined ? updates.summarizedContent : current.summarizedContent
    };

    updateNodeData(nodeId, { mergedTraces: updatedMerged });

    // Trigger trace propagation
    setTimeout(() => {
      get().propagateTraces();
    }, 50);
  },

  // Delete a merged trace
  deleteMergedTrace: (nodeId: string, mergedTraceId: string) => {
    const { nodes, updateNodeData } = get();
    const node = nodes.find(n => n.id === nodeId);
    if (!node) return;

    const existingMerged = node.data.mergedTraces || [];
    const filteredMerged = existingMerged.filter((m: MergedTrace) => m.id !== mergedTraceId);

    updateNodeData(nodeId, { mergedTraces: filteredMerged });

    // Trigger trace propagation
    setTimeout(() => {
      get().propagateTraces();
    }, 50);
  },

  propagateTraces: () => {
    const { nodes, edges } = get();
    
    // We need to calculate traces for each node, AND update edge colors.
    // Topological Sort
    const inDegree = new Map<string, number>();
    const graph = new Map<string, string[]>();
    
    nodes.forEach(node => {
      inDegree.set(node.id, 0);
      graph.set(node.id, []);
    });
    
    edges.forEach(edge => {
      inDegree.set(edge.target, (inDegree.get(edge.target) || 0) + 1);
      graph.get(edge.source)?.push(edge.target);
    });
    
    const topoQueue: string[] = [];
    inDegree.forEach((count, id) => {
      if (count === 0) topoQueue.push(id);
    });
    
    const sortedNodes: string[] = [];
    while (topoQueue.length > 0) {
      const u = topoQueue.shift()!;
      sortedNodes.push(u);
      
      const children = graph.get(u) || [];
      children.forEach(v => {
        inDegree.set(v, (inDegree.get(v) || 0) - 1);
        if (inDegree.get(v) === 0) {
          topoQueue.push(v);
        }
      });
    }
    
    // Map<NodeID, Trace[]>: Traces LEAVING this node
    const nodeOutgoingTraces = new Map<string, Trace[]>();
    // Map<NodeID, Trace[]>: Traces ENTERING this node (to update NodeData)
    const nodeIncomingTraces = new Map<string, Trace[]>();
    // Map<NodeID, string[]>: Merged traces to delete from each node (disconnected sources)
    const nodeMergedTracesToDelete = new Map<string, string[]>();
    // Map<NodeID, Map<MergedTraceId, UpdatedMergedTrace>>: Updated merged traces with new messages
    const nodeUpdatedMergedTraces = new Map<string, Map<string, { messages: Message[], colors: string[] }>>();
    // Map<NodeID, Message[]>: Prepend messages for each node (for recursive prepend chains)
    const nodePrependMessages = new Map<string, Message[]>();
    // Map<NodeID, Trace[]>: Forked traces to keep (cleanup unused ones)
    const nodeForkedTracesToClean = new Map<string, Trace[]>();
    
    // Also track Edge updates (Color AND SourceHandle)
    const updatedEdges = [...edges];
    let edgesChanged = false;
    
    // Iterate
    sortedNodes.forEach(nodeId => {
      const node = nodes.find(n => n.id === nodeId);
      if (!node) return;
      
      // 1. Gather Incoming Traces (regular and prepend)
      const incomingEdges = edges.filter(e => e.target === nodeId);
      const myIncomingTraces: Trace[] = [];
      
      // Map: traceIdToPrepend -> Message[] (messages to prepend to that trace)
      const prependMessages = new Map<string, Message[]>();
    
    incomingEdges.forEach(edge => {
        const parentOutgoing = nodeOutgoingTraces.get(edge.source) || [];
        const targetHandle = edge.targetHandle || '';
        
        // Check if this is a prepend handle
        const isPrependHandle = targetHandle.startsWith('prepend-');
        
        // Special case: prepend connection (from a prepend trace created by onConnect)
        if (isPrependHandle) {
          // Find the source trace - it could be:
          // 1. A prepend trace (prepend-xxx-from-yyy format) 
          // 2. Or any trace from the source handle
          let matchedPrependTrace = parentOutgoing.find(t => edge.sourceHandle === `trace-${t.id}`);
          
          // Fallback: if no exact match, find by sourceHandle pattern
          if (!matchedPrependTrace && edge.sourceHandle?.startsWith('trace-')) {
            const sourceTraceId = edge.sourceHandle.replace('trace-', '');
            matchedPrependTrace = parentOutgoing.find(t => t.id === sourceTraceId);
          }
          
          // Extract the original target trace ID from the prepend handle
          // Format is "prepend-{traceId}" where traceId could be "fork-xxx" or "trace-xxx"
          const targetTraceId = targetHandle.replace('prepend-', '').replace('inherited-', '');
          
          if (matchedPrependTrace && matchedPrependTrace.messages.length > 0) {
            // Prepend the messages from the source trace
            const existing = prependMessages.get(targetTraceId) || [];
            prependMessages.set(targetTraceId, [...existing, ...matchedPrependTrace.messages]);
            
            // Update edge color to match the trace
            const edgeIndex = updatedEdges.findIndex(e => e.id === edge.id);
            if (edgeIndex !== -1) {
              const currentEdge = updatedEdges[edgeIndex];
              if (currentEdge.style?.stroke !== matchedPrependTrace.color) {
                updatedEdges[edgeIndex] = {
                  ...currentEdge,
                  style: { ...currentEdge.style, stroke: matchedPrependTrace.color, strokeWidth: 2 }
                };
              }
            }
          } else {
            // Even if no messages yet, store the prepend trace info for later updates
            // The prepend connection should still work when the source node gets content
            const existing = prependMessages.get(targetTraceId) || [];
            if (!prependMessages.has(targetTraceId)) {
              prependMessages.set(targetTraceId, existing);
            }
          }
          return; // Don't process prepend edges as regular incoming traces
        }
        
        // Find match based on Handle ID
        let matchedTrace = parentOutgoing.find(t => edge.sourceHandle === `trace-${t.id}`);
        
        // If no exact match, try to find a "Semantic Match" (Auto-Reconnect)
        if (!matchedTrace && edge.sourceHandle?.startsWith('trace-')) {
           const oldId = edge.sourceHandle.replace('trace-', '');
           matchedTrace = parentOutgoing.find(t => t.id === `${oldId}_${edge.source}`);
        }
        
        // Fallback: If still no match, and parent has traces, try to connect to the most logical one.
        if (!matchedTrace && parentOutgoing.length > 0) {
           if (!edge.sourceHandle) {
              matchedTrace = parentOutgoing[parentOutgoing.length - 1];
           }
        }
        
        if (matchedTrace) {
           if (isPrependHandle) {
             // This is a prepend connection from a trace handle - extract the target trace ID
             const targetTraceId = targetHandle.replace('prepend-', '').replace('inherited-', '');
             const existing = prependMessages.get(targetTraceId) || [];
             prependMessages.set(targetTraceId, [...existing, ...matchedTrace.messages]);
           } else {
             // Regular incoming trace
             myIncomingTraces.push(matchedTrace);
           }
           
           // Update Edge Visuals & Logical Connection
           const edgeIndex = updatedEdges.findIndex(e => e.id === edge.id);
           if (edgeIndex !== -1) {
             const currentEdge = updatedEdges[edgeIndex];
             const newHandleId = `trace-${matchedTrace.id}`;
             
             // Check if this is a merged trace (need gradient)
             // Use the new properties on Trace object
             const isMergedTrace = matchedTrace.isMerged || matchedTrace.id.startsWith('merged-');
             const mergedColors = matchedTrace.mergedColors || [];
             
             // If colors not on trace, try to find in parent node's mergedTraces (for originator)
             let finalColors = mergedColors;
             if (isMergedTrace && finalColors.length === 0) {
      const parentNode = nodes.find(n => n.id === edge.source);
                const mergedData = parentNode?.data.mergedTraces?.find((m: MergedTrace) => m.id === matchedTrace.id);
                if (mergedData) finalColors = mergedData.colors;
             }
             
             // Create gradient for merged traces
             let gradient: string | undefined;
             if (finalColors.length > 0) {
               const gradientStops = finalColors.map((color: string, idx: number) => 
                 `${color} ${(idx / finalColors.length) * 100}%, ${color} ${((idx + 1) / finalColors.length) * 100}%`
               ).join(', ');
               gradient = `linear-gradient(90deg, ${gradientStops})`;
             }
             
             // Check if we need to update
             // Update if handle changed OR color changed OR merged status/colors changed
             const currentIsMerged = currentEdge.data?.isMerged;
             const currentColors = currentEdge.data?.colors;
             const colorsChanged = JSON.stringify(currentColors) !== JSON.stringify(finalColors);
             
             if (currentEdge.sourceHandle !== newHandleId || 
                 currentEdge.style?.stroke !== matchedTrace.color ||
                 currentIsMerged !== isMergedTrace ||
                 colorsChanged) {
                 
                updatedEdges[edgeIndex] = {
                  ...currentEdge,
                  sourceHandle: newHandleId,
                  type: isMergedTrace ? 'merged' : undefined,
                  style: { ...currentEdge.style, stroke: matchedTrace.color, strokeWidth: 2 },
                  data: { 
                    ...currentEdge.data, 
                    gradient, 
                    isMerged: isMergedTrace,
                    colors: finalColors
                  }
                };
                edgesChanged = true;
             }
           }
        }
      });
      
      // Deduplicate incoming traces by ID (in case multiple edges carry same trace)
      const uniqueIncoming = Array.from(new Map(myIncomingTraces.map(t => [t.id, t])).values());
      nodeIncomingTraces.set(nodeId, uniqueIncoming);
      
      // 2. Generate Outgoing Traces
      // Every incoming trace gets appended with this node's response.
      // PLUS, we always generate a "Self Trace" (Start New) that starts here.
      
      const myResponseMsg: Message[] = [];
      if (node.data.userPrompt) {
        myResponseMsg.push({ 
           id: `${node.id}-user`, // Deterministic ID for stability
           role: 'user', 
           content: node.data.userPrompt 
        });
      }
      if (node.data.response) {
        myResponseMsg.push({ 
           id: `${node.id}-assistant`, 
           role: 'assistant', 
           content: node.data.response 
        });
      }
      
      const myOutgoingTraces: Trace[] = [];
      
      // A. Pass-through traces (append history) - only if there's a downstream edge
      uniqueIncoming.forEach(t => {
        // SIMPLIFICATION: Keep the same Trace ID for pass-through traces.
        // This ensures A-B-C appears as a single continuous trace with the same ID.
        // Only branch/fork traces get new IDs.
        
        const passThroughId = t.id;
        
        // Only create pass-through if there's actually a downstream edge using it
        const hasDownstreamEdge = updatedEdges.some(e => 
          e.source === node.id && 
          (e.sourceHandle === `trace-${passThroughId}`)
        );
        
        if (hasDownstreamEdge) {
          myOutgoingTraces.push({
            ...t,
            id: passThroughId,
            // Keep original sourceNodeId - this is a pass-through, not originated here
            sourceNodeId: t.sourceNodeId,
            messages: [...t.messages, ...myResponseMsg]
          });
        }
      });
      
      // B. Self Trace (New Branch) -> Only create if there's a downstream edge using it
      const selfTraceId = `trace-${node.id}`;
      const selfPrepend = prependMessages.get(selfTraceId) || [];
      
      // Store prepend messages for this node (for recursive prepend chains)
      // This includes any prepend from upstream and this node's own messages
      if (selfPrepend.length > 0 || myResponseMsg.length > 0) {
        nodePrependMessages.set(node.id, [...selfPrepend, ...myResponseMsg]);
      }
      
      // Only add self trace to outgoing if there's actually a downstream edge using it
      // Check if any edge uses this self trace as source
      // Edge sourceHandle format: "trace-{traceId}" where traceId = "trace-{nodeId}"
      // So sourceHandle would be "trace-trace-{nodeId}"
      const hasSelfTraceEdge = updatedEdges.some(e => 
        e.source === node.id && 
        (e.sourceHandle === `trace-${selfTraceId}` || e.sourceHandle === selfTraceId)
      );
      
      if (hasSelfTraceEdge) {
        const selfTrace: Trace = {
          id: selfTraceId,
          sourceNodeId: node.id,
          color: getStableColor(node.id), 
          messages: [...selfPrepend, ...myResponseMsg]
        };
        myOutgoingTraces.push(selfTrace);
      }
      
      // C. Manual Forks - only include forks that have downstream edges
      if (node.data.forkedTraces) {
         // Filter to only forks that are actually being used (have edges)
         const activeForks = node.data.forkedTraces.filter(fork => {
            return updatedEdges.some(e => 
              e.source === node.id && e.sourceHandle === `trace-${fork.id}`
            );
         });
         
         // Update messages for active forks
         const updatedForks = activeForks.map(fork => {
            const forkPrepend = prependMessages.get(fork.id) || [];
            return {
               ...fork,
               messages: [...forkPrepend, ...myResponseMsg] // Prepend + current messages
            };
         });
         myOutgoingTraces.push(...updatedForks);
         
         // Clean up unused forks from node data
         if (activeForks.length !== node.data.forkedTraces.length) {
            nodeForkedTracesToClean.set(nodeId, activeForks);
         }
      }
      
      // D. Merged Traces - recompute messages when source traces change
      // Also check if any source traces are disconnected, and mark for deletion
      const mergedTracesToDelete: string[] = [];
      const updatedMergedMap = new Map<string, { messages: Message[], colors: string[] }>();
      
      if (node.data.mergedTraces && node.data.mergedTraces.length > 0) {
        const { computeMergedMessages } = get();
        
        node.data.mergedTraces.forEach((merged: MergedTrace) => {
          // Check if all source traces are still connected
          const allSourcesConnected = merged.sourceTraceIds.every(id => 
            uniqueIncoming.some(t => t.id === id)
          );
          
          if (!allSourcesConnected) {
            // Mark this merged trace for deletion
            mergedTracesToDelete.push(merged.id);
            return; // Don't add to outgoing traces
          }
          
          // Recompute messages based on the current incoming traces (pass uniqueIncoming for latest data)
          const updatedMessages = computeMergedMessages(node.id, merged.sourceTraceIds, merged.strategy, uniqueIncoming);
          
          // Filter out current node's messages from updatedMessages to avoid duplication
          // (since myResponseMsg will be appended at the end)
          const nodePrefix = `${node.id}-`;
          const filteredMessages = updatedMessages.filter(m => !m.id?.startsWith(nodePrefix));
          
          // Get prepend messages for this merged trace
          const mergedPrepend = prependMessages.get(merged.id) || [];
          
          // Update colors from current traces (preserve multi-colors)
          const updatedColors = merged.sourceTraceIds.flatMap(id => {
            const t = uniqueIncoming.find(trace => trace.id === id);
            if (!t) return [];
            if (t.mergedColors && t.mergedColors.length > 0) return t.mergedColors;
            return t.color ? [t.color] : [];
          });
          
          // Combine all messages for this merged trace
          const mergedMessages = [...mergedPrepend, ...filteredMessages, ...myResponseMsg];
          
          // Store updated data for bulk update later
          updatedMergedMap.set(merged.id, { messages: mergedMessages, colors: updatedColors });
          
          // Create a trace-like object for merged output
          const mergedOutgoing: Trace = {
            id: merged.id,
            sourceNodeId: node.id,
            color: updatedColors[0] || getStableColor(merged.id),
            messages: mergedMessages,
            isMerged: true,
            mergedColors: updatedColors,
            sourceTraceIds: merged.sourceTraceIds
          };
          
          myOutgoingTraces.push(mergedOutgoing);
        });
      }
      
      // Store merged traces to delete for this node
      if (mergedTracesToDelete.length > 0) {
        nodeMergedTracesToDelete.set(nodeId, mergedTracesToDelete);
      }
      
      // Store updated merged trace data for this node
      if (updatedMergedMap.size > 0) {
        nodeUpdatedMergedTraces.set(nodeId, updatedMergedMap);
      }
      
      nodeOutgoingTraces.set(nodeId, myOutgoingTraces);
      
      // Update Node Data with INCOMING traces (for sidebar selection)
      // We store uniqueIncoming in node.data.traces
      // Note: We need to update the node in the `nodes` array, but we are inside the loop.
      // We'll do a bulk set at the end.
    });
    
    // Bulk Update Store
    const uniqTraces = (list: Trace[]) => Array.from(new Map(list.map(t => [t.id, t])).values());
    const uniqMerged = (list: MergedTrace[]) => Array.from(new Map(list.map(m => [m.id, m])).values());

    set(state => ({
      edges: updatedEdges,
      nodes: state.nodes.map(n => {
        const traces = uniqTraces(nodeIncomingTraces.get(n.id) || []);
        const outTraces = uniqTraces(nodeOutgoingTraces.get(n.id) || []);
        const mergedToDelete = nodeMergedTracesToDelete.get(n.id) || [];
        const updatedMerged = nodeUpdatedMergedTraces.get(n.id);
        const cleanedForks = nodeForkedTracesToClean.get(n.id);
        
        // Filter out disconnected merged traces and update messages for remaining ones
        let filteredMergedTraces = uniqMerged((n.data.mergedTraces || []).filter(
          (m: MergedTrace) => !mergedToDelete.includes(m.id)
        ));
        
        // Apply updated messages and colors to merged traces
        if (updatedMerged && updatedMerged.size > 0) {
          filteredMergedTraces = filteredMergedTraces.map((m: MergedTrace) => {
            const updated = updatedMerged.get(m.id);
            if (updated) {
              return { ...m, messages: updated.messages, colors: updated.colors };
            }
            return m;
          });
        }
        
        // Clean up unused forked traces
        const filteredForkedTraces = cleanedForks !== undefined 
          ? cleanedForks 
          : (n.data.forkedTraces || []);
        
        // Update activeTraceIds: remove deleted merged traces and truly orphaned fork traces
        // Preserve all other valid trace selections
        const activeForkIds = filteredForkedTraces.map(f => f.id);
        const incomingTraceIds = traces.map(t => t.id);
        const outgoingTraceIds = outTraces.map(t => t.id);
        const originalActiveIds = n.data.activeTraceIds || [];
        
        const filteredActiveTraceIds = originalActiveIds.filter(
          (id: string) => {
            // Remove deleted merged traces
            if (mergedToDelete.includes(id)) return false;
            // For fork traces: only remove if truly orphaned
            // A fork is NOT orphaned if it's in forkedTraces, incoming traces, or outgoing traces
            if (id.startsWith('fork-')) {
              const isInForkedTraces = activeForkIds.includes(id);
              const isIncomingTrace = incomingTraceIds.includes(id);
              const isOutgoingTrace = outgoingTraceIds.includes(id);
              if (!isInForkedTraces && !isIncomingTrace && !isOutgoingTrace) return false;
            }
            // Keep all other selections
            return true;
          }
        );
        
        return {
          ...n,
          data: {
            ...n.data,
            traces, 
            outgoingTraces: outTraces,
            forkedTraces: filteredForkedTraces,
            mergedTraces: filteredMergedTraces,
            activeTraceIds: filteredActiveTraceIds
          }
        };
      })
    }));
  },
  };
});

export default useFlowStore;