"""ecomm backend — FastAPI app factory + the REST BFF.

SLICE-1 mounts only /healthz; the auth and storefront endpoints (§6.4) grow here in
later slices. create_app() opens the connection pool and self-migrates the database
at startup (INV-1, INV-7): the app boots against empty persistence and applies its
own schema — there is no seed step.
"""
from __future__ import annotations

from contextlib import asynccontextmanager

import psycopg
from fastapi import Depends, FastAPI, Response

from app.platform import config, db
from app.platform.deps import get_conn


def create_app(database_url: str | None = None) -> FastAPI:
    dsn = database_url or config.database_url()

    @asynccontextmanager
    async def lifespan(app: FastAPI):
        app.state.pool = db.open_pool(dsn)
        with app.state.pool.connection() as conn:
            db.migrate(conn)  # self-migrate at startup (INV-1, INV-7)
        try:
            yield
        finally:
            app.state.pool.close()

    app = FastAPI(title="ecomm", version="0.1", lifespan=lifespan)

    @app.get("/healthz")
    def healthz(response: Response, conn: psycopg.Connection = Depends(get_conn)):
        """Liveness + readiness: process up, DB reachable, migrations current (§6.4)."""
        try:
            conn.execute("SELECT 1")
            pending = db.pending_migrations(conn)
        except Exception:
            response.status_code = 503
            return {"status": "unavailable", "reason": "database_unreachable"}
        if pending:
            response.status_code = 503
            return {"status": "unavailable", "reason": "migrations_pending"}
        return {"status": "ok"}

    return app


app = create_app()