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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)
return (
asyncQ.eachSeries(remaining, (migration) => this.runMigration(versionedData, migration))
.then(() => versionedData)
)
// 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((versionedData) => {
if (!versionedData.data) return Promise.reject(new Error('Migrator - Migration returned empty data'))
if (migration.version !== undefined && versionedData.meta.version !== migration.version) return Promise.reject(new Error('Migrator - Migration did not update version number correctly'))
return Promise.resolve(versionedData)
})
)
}
generateInitialState (initState) {
return {
meta: {
version: this.defaultVersion,
},
data: initState,
}
}
}
module.exports = Migrator
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