import { promises as fs } from "node:fs";
import path from "node:path";

import type { Pool } from "pg";

export type AppliedMigration = {
  id: string;
};

type MigrationFile = {
  id: string;
  sql: string;
};

async function loadMigrationFiles(migrationsDir: string): Promise<MigrationFile[]> {
  const files = (await fs.readdir(migrationsDir)).filter((file) => file.endsWith(".sql")).sort();

  return Promise.all(
    files.map(async (file) => ({
      id: file,
      sql: await fs.readFile(path.join(migrationsDir, file), "utf8"),
    }))
  );
}

export async function runMigrations(pool: Pool, migrationsDir = path.resolve(process.cwd(), "migrations")): Promise<AppliedMigration[]> {
  const migrations = await loadMigrationFiles(migrationsDir);
  const client = await pool.connect();

  try {
    await client.query("BEGIN");
    await client.query(`
      CREATE TABLE IF NOT EXISTS schema_migrations (
        id text PRIMARY KEY,
        applied_at timestamptz NOT NULL DEFAULT now()
      )
    `);

    const appliedRows = await client.query<{ id: string }>("SELECT id FROM schema_migrations");
    const appliedIds = new Set(appliedRows.rows.map((row) => row.id));
    const newlyApplied: AppliedMigration[] = [];

    for (const migration of migrations) {
      if (appliedIds.has(migration.id)) {
        continue;
      }

      await client.query(migration.sql);
      await client.query("INSERT INTO schema_migrations(id) VALUES ($1)", [migration.id]);
      newlyApplied.push({ id: migration.id });
    }

    await client.query("COMMIT");
    return newlyApplied;
  } catch (error) {
    await client.query("ROLLBACK");
    throw error;
  } finally {
    client.release();
  }
}