import type { Pool } from "mysql2/promise";
import fs from "fs";
import path from "path";
import { fileURLToPath } from "url";

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const MIGRATIONS_DIR = path.join(__dirname, "..", "migrations");

export async function runMigrations(pool: Pool): Promise<void> {
  await pool.execute(`
    CREATE TABLE IF NOT EXISTS _migrations (
      id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
      filename VARCHAR(255) NOT NULL UNIQUE,
      run_at DATETIME DEFAULT CURRENT_TIMESTAMP
    )
  `);

  const files = fs
    .readdirSync(MIGRATIONS_DIR)
    .filter((f) => f.endsWith(".sql"))
    .sort();

  for (const file of files) {
    const [rows] = await pool.execute<import("mysql2").RowDataPacket[]>(
      "SELECT id FROM _migrations WHERE filename = ?",
      [file]
    );
    if (rows.length > 0) continue;

    const sql = fs.readFileSync(path.join(MIGRATIONS_DIR, file), "utf-8");
    // NOTE: This splitter is intentionally naive — migration files must not
    // contain semicolons inside string literals or block comments.
    const statements = sql
      .split(";")
      .map((s) => s.trim())
      .filter((s) => s.length > 0 && !s.startsWith("--"));

    const conn = await pool.getConnection();
    await conn.beginTransaction();
    try {
      for (const stmt of statements) {
        await conn.execute(stmt);
      }
      await conn.execute("INSERT INTO _migrations (filename) VALUES (?)", [file]);
      await conn.commit();
      console.log(`Migration applied: ${file}`);
    } catch (err) {
      await conn.rollback();
      throw err;
    } finally {
      conn.release();
    }
  }
}