import { promises as fs } from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import { FileMigrationProvider, Migrator } from 'kysely/migration';
import type { Database } from './database.ts';
import type { Logger } from '../../utils/logger.ts';

/**
 * Applies versioned schema migrations from the on-disk migrations folder.
 */
export class MigrationService {
    private readonly debug: Logger;
    private readonly migrator: Migrator;

    /**
     * @param database - Open database whose schema will be migrated.
     * @param debug - Root logger extended with a migrations namespace.
     */
    constructor(database: Database, debug: Logger) {
        // Extend the debug logger to include the migrations namespace.
        this.debug = debug.extend('migrations');

        // Resolve the migrations directory relative to this module file.
        const currentFilePath = fileURLToPath(import.meta.url);
        const currentDirectory = path.dirname(currentFilePath);
        const migrationsPath = path.join(currentDirectory, 'migrations');

        // Create the migrator backed by filesystem migration files.
        this.migrator = new Migrator({
            db: database.db,
            provider: new FileMigrationProvider({
                fs,
                path,
                migrationFolder: migrationsPath,
            }),
        });
    }

    /**
     * Migrates the database to the latest version.
     *
     * Throws when any pending migration fails so startup can abort cleanly.
     */
    async migrateToLatest(): Promise<void> {
        this.debug('migrating database to latest');
        const { error } = await this.migrator.migrateToLatest();

        if (error) {
            const errorInstance = error instanceof Error ? error : new Error(String(error));
            this.debug('migration failed: %O', errorInstance);
            throw errorInstance;
        }

        this.debug('database migrations complete');
    }
}