feat: Allow sorting collections in sidebar (#1870)

closes #1759

Co-authored-by: Tom Moor <tom.moor@gmail.com>

server/utils/collectionIndexing.js

@@ -0,0 +1,39 @@
+// @flow
+import fractionalIndex from "fractional-index";
+import naturalSort from "../../shared/utils/naturalSort";
+import { Collection } from "../models";
+
+export default async function collectionIndexing(teamId: string) {
+  const collections = await Collection.findAll({
+    where: { teamId, deletedAt: null }, //no point in maintaining index of deleted collections.
+    attributes: ["id", "index", "name"],
+  });
+
+  let sortableCollections = collections.map((collection) => {
+    return [collection, collection.index];
+  });
+
+  sortableCollections = naturalSort(
+    sortableCollections,
+    (collection) => collection[0].name
+  );
+
+  //for each collection with null index, use previous collection index to create new index
+  let previousCollectionIndex = null;
+
+  for (const collection of sortableCollections) {
+    if (collection[1] === null) {
+      const index = fractionalIndex(previousCollectionIndex, collection[1]);
+      collection[0].index = index;
+      await collection[0].save();
+    }
+    previousCollectionIndex = collection[0].index;
+  }
+
+  const indexedCollections = {};
+  sortableCollections.forEach((collection) => {
+    indexedCollections[collection[0].id] = collection[0].index;
+  });
+
+  return indexedCollections;
+}