"""PostgreSQL access: a connection pool, one connection per request, and two query helpers."""

import os
from pathlib import Path

import psycopg2.extras
import psycopg2.pool
from flask import Flask, current_app, g

DEFAULT_DATABASE_URL = "postgresql://postgres:postgres@127.0.0.1:5432/postgres"
SCHEMA = Path(__file__).with_name("schema.sql")


def init_app(app: Flask) -> None:
    pool = psycopg2.pool.ThreadedConnectionPool(
        1, 5, os.environ.get("DATABASE_URL", DEFAULT_DATABASE_URL)
    )
    conn = pool.getconn()
    try:
        with conn, conn.cursor() as cur:
            cur.execute(SCHEMA.read_text())
    finally:
        pool.putconn(conn)
    app.extensions["db_pool"] = pool
    app.after_request(_finish_transaction)
    app.teardown_appcontext(_release_connection)


def query(sql: str, params: tuple = ()) -> list[dict]:
    with _connection().cursor(cursor_factory=psycopg2.extras.RealDictCursor) as cur:
        cur.execute(sql, params)
        return cur.fetchall() if cur.description else []


def query_one(sql: str, params: tuple = ()) -> dict | None:
    rows = query(sql, params)
    return rows[0] if rows else None


def _connection():
    if "db" not in g:
        g.db = current_app.extensions["db_pool"].getconn()
    return g.db


def _finish_transaction(response):
    # Commit only successful responses so a 4xx/5xx never leaves partial writes behind.
    conn = g.get("db")
    if conn is not None:
        if response.status_code < 400:
            conn.commit()
        else:
            conn.rollback()
    return response


def _release_connection(_exc):
    conn = g.pop("db", None)
    if conn is not None:
        conn.rollback()  # no-op after commit; discards work if after_request never ran
        current_app.extensions["db_pool"].putconn(conn)