From fd79fc7b91bbab89c06e886a65cd3c062027f6a5 Mon Sep 17 00:00:00 2001
From: Richard Walker <digitalsadhu@gmail.com>
Date: Thu, 8 Mar 2018 13:09:27 +0100
Subject: [PATCH] feat: add hashArray method

---
 lib/common.js       | 30 ++++++++++++++++++++++++++++++
 test/common.test.js |  9 +++++++++
 2 files changed, 39 insertions(+)

diff --git a/lib/common.js b/lib/common.js
index c84440f..49b7eac 100644
--- a/lib/common.js
+++ b/lib/common.js
@@ -115,3 +115,33 @@ module.exports.createTemporaryFilename = fileType => {
     const rand = Math.floor(Math.random() * 1000).toString();
     return `tmp-${Date.now().toString()}-${rand}.${fileType}`;
 };
+
+/**
+ * Hashes an array of hashes into a single hash
+ *
+ * @param {string[]} arr array of hash strings
+ *
+ * @returns {string} a single hash
+ */
+
+function hashArray(arr) {
+    const source = new stream.Readable({ objectMode: true, read() {} });
+    const hasher = new IdHasher();
+
+    source.pipe(hasher);
+
+    return new Promise((resolve, reject) => {
+        hasher.on('finish', () => {
+            resolve(hasher.hash);
+        });
+
+        hasher.on('error', reject);
+
+        for (const hash of arr) {
+            source.push({ id: hash });
+        }
+        source.push(null);
+    });
+}
+
+module.exports.hashArray = hashArray;
diff --git a/test/common.test.js b/test/common.test.js
index 0db5026..4889e11 100644
--- a/test/common.test.js
+++ b/test/common.test.js
@@ -8,6 +8,7 @@ const {
     FileHasher,
     SourceHasher,
     createTemporaryFilename,
+    hashArray,
 } = require('../');
 
 test('SourceHasher() - feed stream source hash', done => {
@@ -102,3 +103,11 @@ test('createTemporaryFilename()', () => {
     const regex = new RegExp(`^tmp-[0-9a-f-]{5,40}.${type}$`);
     expect(createTemporaryFilename(type)).toMatch(regex);
 });
+
+test('hashArray() - takes array of hashes, resolves as a hash', async () => {
+    expect.hasAssertions();
+    const hash = await hashArray(['abc1acb2', 'abc1acb2', 'abc1acb2']);
+    expect(hash).toBe(
+        '31675a591c1f2963a9ee2d48af5e23b352885db705210818d203e2ba2fc752b4'
+    );
+});