feat: modular domain driven boilerplate

platform/database/registrar.ts

@@ -0,0 +1,30 @@
+import type { CreateIndexesOptions, Db, IndexSpecification } from "mongodb";
+
+import { getCollectionsSet } from "./utilities.ts";
+
+/**
+ * Takes a mongo database and registers the event store collections and
+ * indexes defined internally.
+ *
+ * @param db         - Mongo database to register event store collections against.
+ * @param registrars - List of registrars to register with the database.
+ * @param logger     - Logger method to print internal logs.
+ */
+export async function register(db: Db, registrars: Registrar[], logger?: (...args: any[]) => any) {
+  const list = await getCollectionsSet(db);
+  for (const { name, indexes } of registrars) {
+    if (list.has(name) === false) {
+      await db.createCollection(name);
+    }
+    for (const [indexSpec, options] of indexes) {
+      await db.collection(name).createIndex(indexSpec, options);
+      logger?.("Mongo Event Store > Collection '%s' is indexed [%O] with options %O", name, indexSpec, options ?? {});
+    }
+    logger?.("Mongo Event Store > Collection '%s' is registered", name);
+  }
+}
+
+export type Registrar = {
+  name: string;
+  indexes: [IndexSpecification, CreateIndexesOptions?][];
+};