import Database from 'better-sqlite3';

interface Migration {
  id: string;  // unique, immutable — format: NNNN_short_description
  up: (db: InstanceType<typeof Database>) => void;
}

// Append only. Never reorder or remove entries — that would corrupt tracking.
// Each `up` function receives the open DB handle inside an already-open transaction.
const migrations: Migration[] = [
  // Example:
  // {
  //   id: '0001_bookings_add_color',
  //   up: (db) => {
  //     db.exec(`ALTER TABLE bookings ADD COLUMN color TEXT NOT NULL DEFAULT 'blue'`);
  //   },
  // },
];

export function runMigrations(db: InstanceType<typeof Database>): void {
  db.exec(`
    CREATE TABLE IF NOT EXISTS _migrations (
      id         TEXT PRIMARY KEY,
      applied_at TEXT NOT NULL DEFAULT (datetime('now'))
    )
  `);

  const isApplied = db.prepare('SELECT 1 FROM _migrations WHERE id = ?');
  const markApplied = db.prepare('INSERT INTO _migrations (id) VALUES (?)');

  for (const migration of migrations) {
    if (isApplied.get(migration.id)) continue;
    console.log(`[Migrations] Applying: ${migration.id}`);
    db.transaction(() => {
      migration.up(db);
      markApplied.run(migration.id);
    })();
    console.log(`[Migrations] Applied:  ${migration.id}`);
  }
}