migrations - introduce promise-based migrator

1 files changed, 31 insertions, 0 deletions

diff --git a/app/scripts/lib/migrator/index.js b/app/scripts/lib/migrator/index.js
new file mode 100644
index 000000000..02d8c2335
--- /dev/null
+++ b/app/scripts/lib/migrator/index.js
@@ -0,0 +1,31 @@
+const asyncQ = require('async-q')
+
+class Migrator {
+
+  constructor (opts = {}) {
+    let migrations = opts.migrations || []
+    this.migrations = migrations.sort((a, b) => a.version - b.version)
+    let 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 (meta = { version: this.defaultVersion }) {
+    let remaining = this.migrations.filter(migrationIsPending)
+    
+    return (
+      asyncQ.eachSeries(remaining, (migration) => migration.migrate(meta))
+      .then(() => meta)
+    )
+
+    // migration is "pending" if hit has a higher
+    // version number than currentVersion
+    function migrationIsPending(migration) {
+      return migration.version > meta.version
+    }
+  }
+
+}
+
+module.exports = Migrator