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from fastapi import FastAPI, HTTPException
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import StreamingResponse
from app.schemas import NodeRunRequest, NodeRunResponse, MergeStrategy, Role, Message, Context
from app.services.llm import llm_streamer
from dotenv import load_dotenv
import os
load_dotenv()
app = FastAPI(title="ContextFlow Backend")
app.add_middleware(
CORSMiddleware,
allow_origins=["*"],
allow_credentials=True,
allow_methods=["*"],
allow_headers=["*"],
)
@app.get("/")
def read_root():
return {"message": "ContextFlow Backend is running"}
def smart_merge_messages(messages: list[Message]) -> list[Message]:
"""
Merges messages using two steps:
1. Deduplication by ID (to handle diamond dependencies).
2. Merging consecutive messages from the same role.
"""
if not messages:
return []
# 1. Deduplicate by ID, keeping order
seen_ids = set()
deduplicated = []
for msg in messages:
if msg.id not in seen_ids:
deduplicated.append(msg)
seen_ids.add(msg.id)
# 2. Merge consecutive roles
if not deduplicated:
return []
merged = []
current_msg = deduplicated[0].model_copy()
for next_msg in deduplicated[1:]:
if next_msg.role == current_msg.role:
# Merge content
current_msg.content += f"\n\n{next_msg.content}"
# Keep the latest timestamp
current_msg.timestamp = next_msg.timestamp
else:
merged.append(current_msg)
current_msg = next_msg.model_copy()
merged.append(current_msg)
return merged
@app.post("/api/run_node_stream")
async def run_node_stream(request: NodeRunRequest):
"""
Stream the response from the LLM.
"""
# 1. Concatenate all incoming contexts first
raw_messages = []
for ctx in request.incoming_contexts:
raw_messages.extend(ctx.messages)
# 2. Apply Merge Strategy
final_messages = []
if request.merge_strategy == MergeStrategy.SMART:
final_messages = smart_merge_messages(raw_messages)
else:
# RAW strategy: just keep them as is
final_messages = raw_messages
execution_context = Context(messages=final_messages)
return StreamingResponse(
llm_streamer(execution_context, request.user_prompt, request.config),
media_type="text/event-stream"
)
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