"""Wait for the database to accept connections before booting the app.

For SQLite (current setup) this is effectively a no-op — the file is
created on first connection. The script exists as scaffolding for a
future move to Postgres, where the entrypoint must wait for the DB
container to come up before `flask db upgrade` will succeed.

Exit codes:
  0  — DB is reachable
  1  — gave up after MAX_WAIT_SECONDS
"""
import os
import sys
import time

from sqlalchemy import create_engine, text
from sqlalchemy.exc import OperationalError

import config as app_config

MAX_WAIT_SECONDS = int(os.environ.get('DB_WAIT_TIMEOUT', '30'))
POLL_INTERVAL = 1.0


def main() -> int:
    uri = app_config.Config.SQLALCHEMY_DATABASE_URI

    # SQLite needs no wait — sqlite:/// URIs always succeed once the dir exists.
    if uri.startswith('sqlite:'):
        print(f'[wait_for_db] SQLite ({uri}) — no wait needed')
        return 0

    engine = create_engine(uri, pool_pre_ping=True)
    deadline = time.monotonic() + MAX_WAIT_SECONDS
    attempt = 0
    while True:
        attempt += 1
        try:
            with engine.connect() as conn:
                conn.execute(text('SELECT 1'))
            print(f'[wait_for_db] connected after {attempt} attempt(s)')
            return 0
        except OperationalError as e:
            if time.monotonic() >= deadline:
                print(f'[wait_for_db] gave up after {MAX_WAIT_SECONDS}s: {e}',
                      file=sys.stderr)
                return 1
            time.sleep(POLL_INTERVAL)


if __name__ == '__main__':
    sys.exit(main())