class Migrator {
constructor ( opts = { } ) {
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 ( ) ) {
const pendingMigrations = this . migrations . filter ( migrationIsPending )
for ( let index in pendingMigrations ) {
let migration = pendingMigrations [ index ]
versionedData = await migration . migrate ( versionedData )
if ( ! versionedData . data ) throw new Error ( 'Migrator - migration returned empty data' )
if ( versionedData . version !== undefined && versionedData . meta . version !== migration . version ) throw new Error ( 'Migrator - Migration did not update version number correctly' )
}
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