/**
 * Migration runner
 *
 * How it works:
 *  1. Creates a `_migrations` table on first run.
 *  2. Loads all migration modules from ./migrations/ in filename order.
 *  3. Skips any migration whose `id` is already recorded in `_migrations`.
 *  4. Executes pending migrations inside individual transactions.
 *  5. Records each successful migration with a timestamp.
 *
 * Adding a new migration:
 *  - Create `apps/server/src/db/migrations/NNN_description.ts`
 *  - Export `id` (string, matches filename) and `up` (SQL string).
 *  - Optionally export `down` (SQL string) for rollback support.
 *  - The runner picks it up automatically on next startup.
 */

import db from './db';
import path from 'path';
import fs from 'fs';

interface Migration {
  id: string;
  up: string;
  down?: string;
}

function bootstrap() {
  db.exec(`
    CREATE TABLE IF NOT EXISTS _migrations (
      id         TEXT    PRIMARY KEY,
      applied_at TEXT    NOT NULL DEFAULT (datetime('now'))
    );
  `);
}

function loadMigrations(): Migration[] {
  const dir = path.join(__dirname, 'migrations');
  if (!fs.existsSync(dir)) return [];

  return fs
    .readdirSync(dir)
    .filter((f) => f.endsWith('.ts') || f.endsWith('.js'))
    .sort()
    .map((file) => {
      // eslint-disable-next-line @typescript-eslint/no-var-requires
      const mod = require(path.join(dir, file)) as Migration;
      if (!mod.id || !mod.up) {
        throw new Error(`Migration ${file} must export 'id' and 'up'`);
      }
      return mod;
    });
}

function getApplied(): Set<string> {
  const rows = db.prepare('SELECT id FROM _migrations').all() as { id: string }[];
  return new Set(rows.map((r) => r.id));
}

export function runMigrations() {
  bootstrap();

  const migrations = loadMigrations();
  const applied = getApplied();
  const pending = migrations.filter((m) => !applied.has(m.id));

  if (pending.length === 0) {
    console.log('[db] All migrations up to date.');
    return;
  }

  console.log(`[db] Running ${pending.length} pending migration(s)...`);

  for (const migration of pending) {
    const apply = db.transaction(() => {
      db.exec(migration.up);
      db.prepare('INSERT INTO _migrations (id) VALUES (?)').run(migration.id);
    });

    try {
      apply();
      console.log(`[db]  ✓ Applied: ${migration.id}`);
    } catch (err) {
      console.error(`[db]  ✗ Failed:  ${migration.id}`, err);
      throw err; // Abort startup on migration failure
    }
  }

  console.log('[db] Migrations complete.');
}

export function rollback(targetId: string) {
  const migrations = loadMigrations();
  const applied = getApplied();

  // Find all applied migrations after targetId in reverse order
  const toRollback = migrations
    .filter((m) => applied.has(m.id) && m.id > targetId)
    .reverse();

  if (toRollback.length === 0) {
    console.log('[db] Nothing to roll back.');
    return;
  }

  for (const migration of toRollback) {
    if (!migration.down) {
      console.warn(`[db]  ⚠ No down migration for: ${migration.id} — skipping`);
      continue;
    }
    const revert = db.transaction(() => {
      db.exec(migration.down!);
      db.prepare('DELETE FROM _migrations WHERE id = ?').run(migration.id);
    });
    try {
      revert();
      console.log(`[db]  ✓ Rolled back: ${migration.id}`);
    } catch (err) {
      console.error(`[db]  ✗ Rollback failed: ${migration.id}`, err);
      throw err;
    }
  }
}