from fastapi import FastAPI, HTTPException, Request
from fastapi.middleware.cors import CORSMiddleware
from fastapi.responses import JSONResponse
from pydantic import BaseModel
from typing import List
import jwt
import datetime
from dotenv import load_dotenv
import os

load_dotenv()

# FastAPI app setup
app = FastAPI()

# CORS setup to allow cross-origin requests
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],  # Allow all origins; use specific domains for security
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

# Secret key for JWT encoding/decoding
SECRET_KEY = os.getenv("SECRET_KEY", "secret")  # Use a more secure key in production
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30  # Token expiration time in minutes

# Temporary user dictionary for storing credentials
USERS = {
    "user1": "password1",
    "user2": "password2",
}

# Pydantic model to define the structure of user data
class User(BaseModel):
    username: str
    password: str

# JWT token generation function
def create_access_token(data: dict, expires_delta: datetime.timedelta = None):
    """Create a new JWT token."""
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.datetime.utcnow() + expires_delta
    else:
        expire = datetime.datetime.utcnow() + datetime.timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)

# JWT token verification function
def verify_access_token(token: str):
    """Verify and decode the JWT token."""
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        return payload
    except jwt.ExpiredSignatureError:
        raise HTTPException(status_code=401, detail="Token has expired")
    except jwt.DecodeError:
        raise HTTPException(status_code=401, detail="Token is invalid")
    except Exception as e:
        # Catch any other exception and raise a generic HTTP 400 error
        raise HTTPException(status_code=400, detail=f"An error occurred: {str(e)}")

# Register a new user
@app.post("/register")
async def register_user(user: User):
    """Register a new user."""
    if user.username in USERS:
        raise HTTPException(status_code=400, detail="Username already exists")
    USERS[user.username] = user.password
    return {"message": "User registered successfully"}

# Login a user and generate a JWT session token
@app.post("/login")
async def login_user(user: User):
    """Authenticate a user and return JWT token."""
    if user.username not in USERS or USERS[user.username] != user.password:
        raise HTTPException(status_code=401, detail="Invalid credentials")
    # Create JWT token
    access_token = create_access_token(data={"sub": user.username})
    return {"token": access_token}

# API to validate the session token
@app.get("/api/validate-token")
async def validate_token(token: str):
    """Validate the JWT token."""
    payload = verify_access_token(token)
    return {"message": "Token is valid", "username": payload.get("sub")}

# Search for users by username
@app.get("/search")
async def search_users(query: str) -> List[str]:
    """Search for users by username."""
    matching_users = [username for username in USERS if query.lower() in username.lower()]
    if not matching_users:
        raise HTTPException(status_code=404, detail="No users found matching the query")
    return matching_users

# API routes for CRUD operations
@app.get("/api/users")
async def get_all_users() -> List[str]:
    """Get a list of all users."""
    return list(USERS.keys())

@app.get("/api/user/{username}")
async def get_user(username: str):
    """Get details of a specific user."""
    if username not in USERS:
        raise HTTPException(status_code=404, detail="User not found")
    return {"username": username, "password": USERS[username]}

@app.delete("/api/user/{username}")
async def delete_user(username: str):
    """Delete a specific user."""
    if username not in USERS:
        raise HTTPException(status_code=404, detail="User not found")
    del USERS[username]
    return {"message": f"User {username} deleted successfully"}

@app.put("/api/user/{username}")
async def update_user(username: str, user: User):
    """Update a user's password."""
    if username not in USERS:
        raise HTTPException(status_code=404, detail="User not found")
    USERS[username] = user.password
    return {"message": f"User {username} password updated successfully"}

@app.get("/api/user-exists/{username}")
async def user_exists(username: str):
    """Check if a user exists based on the username."""
    if username in USERS:
        return {"message": f"User '{username}' exists"}
    raise HTTPException(status_code=404, detail="User not found")

# Global error handling middleware
@app.middleware("http")
async def custom_error_handler(request: Request, call_next):
    try:
        response = await call_next(request)
        return response
    except HTTPException as exc:
        return JSONResponse(
            status_code=exc.status_code,
            content={"detail": exc.detail}
        )
    except Exception as e:
        return JSONResponse(
            status_code=500,
            content={"detail": "Internal Server Error"}
        )