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const EventEmitter = require('events')
class Migrator extends EventEmitter {
constructor (opts = {}) {
super()
const migrations = opts.migrations || []
// sort migrations by version
this.migrations = migrations.sort((a, b) => a.version - b.version)
// grab migration with highest 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
async migrateData (versionedData = this.generateInitialState()) {
// get all migrations that have not yet been run
const pendingMigrations = this.migrations.filter(migrationIsPending)
// perform each migration
for (const index in pendingMigrations) {
const migration = pendingMigrations[index]
try {
// attempt migration and validate
const migratedData = await migration.migrate(versionedData)
if (!migratedData.data) throw new Error('Migrator - migration returned empty data')
if (migratedData.version !== undefined && migratedData.meta.version !== migration.version) throw new Error('Migrator - Migration did not update version number correctly')
// accept the migration as good
versionedData = migratedData
} catch (err) {
// emit error instead of throw so as to not break the run (gracefully fail)
const error = new Error(`MetaMask Migration Error #${version}:\n${err.stack}`)
this.emit('error', error)
// stop migrating and use state as is
return versionedData
}
}
return versionedData
// migration is "pending" if it has a higher
// version number than currentVersion
function migrationIsPending (migration) {
return migration.version > versionedData.meta.version
}
}
generateInitialState (initState) {
return {
meta: {
version: this.defaultVersion,
},
data: initState,
}
}
}
module.exports = Migrator
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