from fastapi import FastAPI, HTTPException, Response, Depends
from sqlmodel import Session, select
from typing import Annotated
import datetime, re

from database.feed import Feed, FeedCreate, FeedPublic, FeedUpdate
from utils.feed_generator import generate_feed_of_user, USER_NOT_FOUND, CANNOT_ACCESS_INSTANCE
from utils.database import get_session, create_db_and_tables

app = FastAPI()
SessionDep = Annotated[Session, Depends(get_session)]


@app.on_event("startup")
def on_startup():
    create_db_and_tables()


@app.get("/feed/{user_handle}")
def get_feed_of_user(user_handle: str, session: SessionDep):
    # validate user's handle
    HANDLE_PATTERN = "@[a-zA-Z0-9_]+@[^\t\n\r\f\v]+"
    if re.match(HANDLE_PATTERN, user_handle) is None:
        return HTTPException(status_code=400, detail="The handle is invalid.")

    # get feed on database
    feed_db = session.exec(select(Feed).where(Feed.handle == user_handle)).first()
    
    # return cached feed if it has been cached for less than 10 minutes
    if feed_db and ((feed_db.updated_at + datetime.timedelta(minutes=10)) - datetime.datetime.now()).total_seconds() > 0:
        return Response(content=feed_db.feed, media_type="application/xml")

    feed = generate_feed_of_user(user_handle)

    if feed == USER_NOT_FOUND:
        return HTTPException(status_code=404, detail="The user cannot be found.")
    if feed == CANNOT_ACCESS_INSTANCE:
        return HTTPException(status_code=400, detail="Cannot access the instance.")
    
    # cache new feed
    if feed_db:
        feed_data = FeedUpdate(feed=feed, updated_at=datetime.datetime.now()).model_dump(exclude_unset=True)
        feed_db.sqlmodel_update(feed_data)
    else:
        feed_db = Feed.model_validate(FeedCreate(handle=user_handle, feed=feed))
    session.add(feed_db)
    session.commit()
    session.refresh(feed_db)
    
    return Response(content=feed, media_type="application/xml")