From 4495a1ac67532a4703afd0a738ae4a75dd4411c3 Mon Sep 17 00:00:00 2001
From: Evan Hahn <69474926+EvanHahn-Signal@users.noreply.github.com>
Date: Mon, 28 Jun 2021 16:46:33 -0500
Subject: [PATCH] Add `reduce` iterables utility

---
 ts/ConversationController.ts        |  5 +++--
 ts/test-both/util/iterables_test.ts | 18 ++++++++++++++++++
 ts/util/iterables.ts                | 12 ++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/ts/ConversationController.ts b/ts/ConversationController.ts
index bb028b1997..9f3aeee133 100644
--- a/ts/ConversationController.ts
+++ b/ts/ConversationController.ts
@@ -1,7 +1,7 @@
 // Copyright 2020-2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-import { debounce, reduce, uniq, without } from 'lodash';
+import { debounce, uniq, without } from 'lodash';
 import PQueue from 'p-queue';
 
 import dataInterface from './sql/Client';
@@ -13,6 +13,7 @@ import { SendOptionsType, CallbackResultType } from './textsecure/SendMessage';
 import { ConversationModel } from './models/conversations';
 import { maybeDeriveGroupV2Id } from './groups';
 import { assert } from './util/assert';
+import { map, reduce } from './util/iterables';
 import { isGroupV1, isGroupV2 } from './util/whatTypeOfConversation';
 import { deprecated } from './util/deprecated';
 import { getSendOptions } from './util/getSendOptions';
@@ -103,7 +104,7 @@ export function start(): void {
       };
 
       const newUnreadCount = reduce(
-        this.map((m: ConversationModel) =>
+        map(this, (m: ConversationModel) =>
           canCount(m) ? getUnreadCount(m) : 0
         ),
         (item: number, memo: number) => (item || 0) + memo,
diff --git a/ts/test-both/util/iterables_test.ts b/ts/test-both/util/iterables_test.ts
index 31299f871b..02b02c7197 100644
--- a/ts/test-both/util/iterables_test.ts
+++ b/ts/test-both/util/iterables_test.ts
@@ -11,6 +11,7 @@ import {
   groupBy,
   isIterable,
   map,
+  reduce,
   size,
   take,
 } from '../../util/iterables';
@@ -311,6 +312,23 @@ describe('iterable utilities', () => {
     });
   });
 
+  describe('reduce', () => {
+    it('returns the accumulator when passed an empty iterable', () => {
+      const fn = sinon.fake();
+
+      assert.strictEqual(reduce([], fn, 123), 123);
+
+      sinon.assert.notCalled(fn);
+    });
+
+    it('iterates over the iterable, ultimately returning a result', () => {
+      assert.strictEqual(
+        reduce(new Set([1, 2, 3, 4]), (result, n) => result + n, 89),
+        99
+      );
+    });
+  });
+
   describe('take', () => {
     it('returns the first n elements from an iterable', () => {
       const everyNumber = {
diff --git a/ts/util/iterables.ts b/ts/util/iterables.ts
index d390e53fc9..10897814c3 100644
--- a/ts/util/iterables.ts
+++ b/ts/util/iterables.ts
@@ -155,6 +155,18 @@ class MapIterator<T, ResultT> implements Iterator<ResultT> {
   }
 }
 
+export function reduce<T, TResult>(
+  iterable: Iterable<T>,
+  fn: (result: TResult, value: T) => TResult,
+  accumulator: TResult
+): TResult {
+  let result = accumulator;
+  for (const value of iterable) {
+    result = fn(result, value);
+  }
+  return result;
+}
+
 export function take<T>(iterable: Iterable<T>, amount: number): Iterable<T> {
   return new TakeIterable(iterable, amount);
 }