import {
  MigrationOperation,
  SessionStorageMigrator,
  SessionStorageMigratorOptions,
  defaultSessionStorageMigratorOptions,
  DBConnection,
} from './types';

export abstract class AbstractMigrationEngine<
  ConnectionType extends DBConnection,
  MigratorOptionType extends SessionStorageMigratorOptions,
> implements SessionStorageMigrator {
  protected options: SessionStorageMigratorOptions;
  protected connection: ConnectionType;
  protected ready: Promise<void>;
  protected migrations: MigrationOperation[];

  constructor(
    db: ConnectionType,
    opts: Partial<MigratorOptionType> = {},
    migrations: MigrationOperation[],
  ) {
    this.options = {...defaultSessionStorageMigratorOptions, ...opts};
    this.connection = db;
    this.migrations = migrations;

    this.ready = this.initMigrationPersistence();
  }

  async applyMigrations(databaseReady: Promise<void>): Promise<void> {
    await databaseReady;
    await this.ready;

    for (const {migrationName, migrationFunction} of this.getMigrationList()) {
      const migrationApplied =
        await this.hasMigrationBeenApplied(migrationName);
      if (!migrationApplied) {
        await migrationFunction(this.connection);
        await this.saveAppliedMigration(migrationName);
      }
    }
    return Promise.resolve();
  }

  getMigrationList(): MigrationOperation[] {
    return this.migrations;
  }

  abstract initMigrationPersistence(): Promise<void>;
  abstract hasMigrationBeenApplied(migrationName: string): Promise<boolean>;
  abstract saveAppliedMigration(migrationName: string): Promise<void>;
}