from fastapi import APIRouter, Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from sqlalchemy.orm import Session
from typing import Optional
from pydantic import BaseModel

from .models import User, get_db
from .utils import (
    Token, UserCreate, UserLogin, UserResponse,
    verify_password, get_password_hash, create_access_token, decode_token
)

router = APIRouter(prefix="/api/auth", tags=["Authentication"])

# OAuth2 scheme for token extraction
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login", auto_error=True)
oauth2_scheme_optional = OAuth2PasswordBearer(tokenUrl="/api/auth/login", auto_error=False)


async def get_current_user(
    token: str = Depends(oauth2_scheme),
    db: Session = Depends(get_db)
) -> User:
    """
    Dependency: Validate JWT token and return current user.
    Raises 401 if token is invalid or user not found.
    """
    username = decode_token(token)
    if not username:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid or expired token",
            headers={"WWW-Authenticate": "Bearer"},
        )
    
    user = db.query(User).filter(User.username == username).first()
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="User not found",
            headers={"WWW-Authenticate": "Bearer"},
        )
    
    if not user.is_active:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="User account is disabled"
        )
    
    return user


async def get_current_user_optional(
    token: Optional[str] = Depends(oauth2_scheme_optional),
    db: Session = Depends(get_db)
) -> Optional[User]:
    """
    Dependency: Try to get current user, but don't fail if not authenticated.
    Returns None if no valid token.
    """
    if not token:
        return None
    
    username = decode_token(token)
    if not username:
        return None
    
    user = db.query(User).filter(User.username == username).first()
    if not user or not user.is_active:
        return None
    
    return user


@router.get("/check-username/{username}")
async def check_username(username: str, db: Session = Depends(get_db)):
    """
    Check if a username is available.
    """
    existing = db.query(User).filter(User.username == username).first()
    return {"available": existing is None}


@router.get("/check-email/{email}")
async def check_email(email: str, db: Session = Depends(get_db)):
    """
    Check if an email is available.
    """
    existing = db.query(User).filter(User.email == email).first()
    return {"available": existing is None}


@router.post("/register", response_model=UserResponse, status_code=status.HTTP_201_CREATED)
async def register(user_data: UserCreate, db: Session = Depends(get_db)):
    """
    Register a new user account.
    """
    # Check if username already exists
    existing_user = db.query(User).filter(User.username == user_data.username).first()
    if existing_user:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Username already registered"
        )
    
    # Check if email already exists
    existing_email = db.query(User).filter(User.email == user_data.email).first()
    if existing_email:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Email already registered"
        )
    
    # Validate password length
    if len(user_data.password) < 6:
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Password must be at least 6 characters"
        )
    
    # Create new user
    user = User(
        username=user_data.username,
        email=user_data.email,
        hashed_password=get_password_hash(user_data.password)
    )
    db.add(user)
    db.commit()
    db.refresh(user)
    
    return user


@router.post("/login", response_model=Token)
async def login(form_data: OAuth2PasswordRequestForm = Depends(), db: Session = Depends(get_db)):
    """
    Login with username and password, returns JWT token.
    """
    # Find user by username
    user = db.query(User).filter(User.username == form_data.username).first()
    
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )
    
    if not verify_password(form_data.password, user.hashed_password):
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )
    
    if not user.is_active:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="User account is disabled"
        )
    
    # Create access token
    access_token = create_access_token(data={"sub": user.username})
    
    return {
        "access_token": access_token,
        "token_type": "bearer",
        "username": user.username
    }


@router.post("/login/json", response_model=Token)
async def login_json(user_data: UserLogin, db: Session = Depends(get_db)):
    """
    Login with JSON body (alternative to form-data).
    """
    # Find user by username
    user = db.query(User).filter(User.username == user_data.username).first()
    
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
        )
    
    if not verify_password(user_data.password, user.hashed_password):
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
        )
    
    if not user.is_active:
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail="User account is disabled"
        )
    
    # Create access token
    access_token = create_access_token(data={"sub": user.username})
    
    return {
        "access_token": access_token,
        "token_type": "bearer",
        "username": user.username
    }


@router.get("/me", response_model=UserResponse)
async def get_me(current_user: User = Depends(get_current_user)):
    """
    Get current authenticated user's info.
    """
    return current_user


@router.get("/api-keys")
async def get_api_keys(current_user: User = Depends(get_current_user)):
    """
    Get current user's API keys (masked for security).
    """
    def mask_key(key: str | None) -> str:
        if not key:
            return ""
        if len(key) <= 8:
            return "*" * len(key)
        return key[:4] + "*" * (len(key) - 8) + key[-4:]
    
    return {
        "openai_api_key": mask_key(current_user.openai_api_key),
        "gemini_api_key": mask_key(current_user.gemini_api_key),
        "has_openai_key": bool(current_user.openai_api_key),
        "has_gemini_key": bool(current_user.gemini_api_key),
    }


class ApiKeysUpdate(BaseModel):
    openai_api_key: Optional[str] = None
    gemini_api_key: Optional[str] = None


@router.post("/api-keys")
async def update_api_keys(
    keys: ApiKeysUpdate,
    current_user: User = Depends(get_current_user),
    db: Session = Depends(get_db)
):
    """
    Update current user's API keys.
    Pass empty string to clear a key, or omit to keep unchanged.
    """
    if keys.openai_api_key is not None:
        current_user.openai_api_key = keys.openai_api_key if keys.openai_api_key else None
    
    if keys.gemini_api_key is not None:
        current_user.gemini_api_key = keys.gemini_api_key if keys.gemini_api_key else None
    
    db.commit()
    
    return {"message": "API keys updated successfully"}


@router.post("/logout")
async def logout():
    """
    Logout endpoint (client should discard the token).
    JWT tokens are stateless, so this is just for API completeness.
    """
    return {"message": "Successfully logged out"}