import asyncio
from fastapi import FastAPI, Request
from fastapi.middleware.cors import CORSMiddleware

from fastapi.responses import StreamingResponse
from pydantic import BaseModel
import datetime

# Use of Pydantic class for automatic request validation in FastAPI
class Message(BaseModel):
    message: str

app = FastAPI()

# This middleware allows other origins to communicate with us
app.add_middleware(
    CORSMiddleware, # https://developer.mozilla.org/en-US/docs/Web/HTTP/Guides/CORS
    allow_origins=["http://localhost:5173"], # address of our UI application
    allow_methods=["*"], # GET, POST, etc.
)

# Endpoint to receive messages from the UI
@app.post("/message")
async def receive_message(message: Message):
    """
    Receives a message from the UI and prints it to the console.
    """
    print(f"Received message: {message}")
    return { "status": "Message received" }

# Endpoint for Server-Sent Events (SSE)
@app.get("/sse")
async def sse_endpoint(request: Request):
    """
    Endpoint for Server-Sent Events.
    """
    async def event_generator():
        while True:
            # If connection to client closes, stop sending events
            if await request.is_disconnected():
                break
            
            # Send message containing current time every second
            current_time = datetime.datetime.now().strftime("%H:%M:%S")
            yield f"data: Server time: {current_time}\n\n" # \n\n is needed to separate events (SSE is text-based)
            await asyncio.sleep(1)

    return StreamingResponse(event_generator(), media_type="text/event-stream") # media_type specifies that this connection is for event streams