"""FastAPI application factory (SPEC §2 ``app/main.py``)."""

from __future__ import annotations

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager

from fastapi import FastAPI
from sqlalchemy import text

from app.config import get_settings
from app.db import dispose_engine, get_engine
from app.redis_client import close_redis, get_redis


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    """Warm shared resources on startup, dispose them on shutdown."""
    # Touch settings early so misconfiguration fails fast.
    get_settings()
    yield
    await close_redis()
    await dispose_engine()


def create_app() -> FastAPI:
    """Construct the FastAPI application."""
    app = FastAPI(title="Webmail", version="0.1.0", lifespan=lifespan)

    from app.api.errors import register_error_handlers

    register_error_handlers(app)

    @app.get("/api/healthz")
    async def healthz() -> dict[str, str]:
        """Liveness/readiness probe: checks DB and Redis (dev-setup §6)."""
        async with get_engine().connect() as conn:
            await conn.execute(text("SELECT 1"))
        await get_redis().ping()
        return {"status": "ok"}

    from app.api import register_routers

    register_routers(app)
    return app