rfc-app/backend/app/main.py

"""FastAPI entrypoint.

Wires the §17 routers, the OAuth callbacks, the webhook receiver, and
the background reconciler. Per §4.2, single process, colocated SQLite —
no need for a separate worker.
"""
from __future__ import annotations

import logging
import secrets
from contextlib import asynccontextmanager

from fastapi import APIRouter, FastAPI, HTTPException, Request
from fastapi.responses import RedirectResponse
from starlette.middleware.sessions import SessionMiddleware

from . import api as api_routes, auth, cache, db, providers as providers_mod, webhooks
from .bot import Bot
from .config import load_config
from .gitea import Gitea

logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(name)s %(message)s")
log = logging.getLogger("rfc_app")


@asynccontextmanager
async def lifespan(app: FastAPI):
    config = load_config()
    db.run_migrations(config)
    db.init(config)
    gitea = Gitea(config)
    bot = Bot(gitea)
    reconciler = cache.Reconciler(config, gitea)

    # §18 carryover: the multi-provider LLM abstraction. Provider
    # construction can fail (missing key, wrong env value) — if it does,
    # the rest of the app still serves; chat endpoints surface a clear
    # 503 instead of crashing the process.
    try:
        providers = providers_mod.load_from_config(config)
    except Exception:
        log.exception("provider construction failed; chat will be disabled")
        providers = {}

    app.state.config = config
    app.state.gitea = gitea
    app.state.bot = bot
    app.state.reconciler = reconciler
    app.state.providers = providers

    app.include_router(_oauth_router(config))
    app.include_router(api_routes.make_router(config, gitea, bot, providers))
    app.include_router(webhooks.make_router(config, gitea))

    reconciler.start()
    log.info("RFC app started — meta repo %s/%s", config.gitea_org, config.meta_repo)
    try:
        yield
    finally:
        await reconciler.stop()
        await gitea.close()


def create_app() -> FastAPI:
    # The secret key is required at app construction (SessionMiddleware
    # is added before lifespan runs), so we read just that one value
    # eagerly via load_config(). Everything else waits for lifespan.
    config = load_config()
    app = FastAPI(lifespan=lifespan)
    app.add_middleware(
        SessionMiddleware,
        secret_key=config.secret_key,
        session_cookie="rfc_session",
        max_age=60 * 60 * 24 * 30,
        https_only=False,
    )
    return app


app = create_app()


def _oauth_router(config) -> APIRouter:
    router = APIRouter()

    @router.get("/auth/login")
    async def login(request: Request):
        state = auth.new_state()
        request.session[auth.SESSION_STATE_KEY] = state
        return RedirectResponse(auth.authorization_url(config, state))

    @router.get("/auth/callback")
    async def callback(request: Request, code: str = "", state: str = ""):
        if not code:
            raise HTTPException(400, "Missing code")
        stored_state = request.session.get(auth.SESSION_STATE_KEY)
        if not stored_state or not secrets.compare_digest(stored_state, state):
            raise HTTPException(400, "Invalid state")
        token_data = await auth.exchange_code(config, code)
        access_token = token_data.get("access_token")
        if not access_token:
            raise HTTPException(400, "Token exchange failed")
        profile = await auth.fetch_user_profile(config, access_token)
        user = auth.provision_user(config, profile)
        auth.store_session(request, user)
        return RedirectResponse("/")

    @router.get("/auth/logout")
    async def logout(request: Request):
        request.session.clear()
        return RedirectResponse("/")

    return router