const asyncQ = require('async-q') class Migrator { constructor (opts = {}) { const migrations = opts.migrations || [] this.migrations = migrations.sort((a, b) => a.version - b.version) const lastMigration = this.migrations.slice(-1)[0] // use specified defaultVersion or highest migration version this.defaultVersion = opts.defaultVersion || (lastMigration && lastMigration.version) || 0 } // run all pending migrations on meta in place migrateData (versionedData = this.generateInitialState()) { const remaining = this.migrations.filter(migrationIsPending) if (remaining.length === 0) return versionedData return ( asyncQ.eachSeries(remaining, (migration) => this.runMigration(versionedData, migration)) .then((migratedData) => migratedData.pop()) ) // migration is "pending" if hit has a higher // version number than currentVersion function migrationIsPending (migration) { return migration.version > versionedData.meta.version } } runMigration (versionedData, migration) { return migration.migrate(versionedData) .then((migratedData) => { if (!migratedData.data) return Promise.reject(new Error('Migrator - Migration returned empty data')) if (migration.version !== undefined && migratedData.meta.version !== migration.version) return Promise.reject(new Error('Migrator - Migration did not update version number correctly')) return Promise.resolve(migratedData) }) } generateInitialState (initState) { return { meta: { version: this.defaultVersion, }, data: initState, } } } module.exports = Migrator