From 990549b774668c1da2ce51fb1cfed9e3efaeb8c3 Mon Sep 17 00:00:00 2001
From: Pierre Inglebert <pierre.inglebert@gmail.com>
Date: Tue, 31 Mar 2015 08:49:40 +0200
Subject: [PATCH] add patches merging

---
 README.md         |  5 +++
 lib/merge.js      | 20 +++++++++++
 test/lib/merge.js | 85 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 110 insertions(+)
 create mode 100644 lib/merge.js
 create mode 100644 test/lib/merge.js

diff --git a/README.md b/README.md
index 6e8892a..745b05f 100644
--- a/README.md
+++ b/README.md
@@ -80,6 +80,11 @@ Applies `patch` on `obj`.
 
 Generates a `patch` Object from source and target Object.
 
+
+#### jsonmergepatch.merge (`patch1` Object, `patch2` Object) : `patch` Object
+
+Generates a `patch` Object by merging patch1 and patch2.
+
 ## Running tests
 
 ```sh
diff --git a/lib/merge.js b/lib/merge.js
new file mode 100644
index 0000000..86eedbb
--- /dev/null
+++ b/lib/merge.js
@@ -0,0 +1,20 @@
+'use strict';
+
+module.exports = function merge(patch1, patch2) {
+  if(patch1 === null || patch2 === null ||
+    typeof patch1 !== 'object' || typeof patch2 !== 'object' ||
+    Array.isArray(patch1) !== Array.isArray(patch2)) {
+    return patch2;
+  }
+  var patch = JSON.parse(JSON.stringify(patch1));
+
+	Object.keys(patch2)
+  .forEach(function(key) {
+		if(patch1[key] !== undefined) {
+  		patch[key] = merge(patch1[key], patch2[key]);
+		} else {
+			patch[key] = patch2[key];
+		}
+  });
+	return patch;
+};
diff --git a/test/lib/merge.js b/test/lib/merge.js
new file mode 100644
index 0000000..98d0c28
--- /dev/null
+++ b/test/lib/merge.js
@@ -0,0 +1,85 @@
+'use strict';
+
+var assert = require('chai').assert;
+
+var merge = require('../../lib/merge');
+
+describe('merge', function() {
+
+	it('should merge 2 patches with different attributes', function() {
+		assert.deepEqual(
+			merge({a: 'b'}, {b: 'c'}),
+	    {a: 'b', b: 'c'}
+    );
+	});
+
+	it('should merge take last patch attributes for rewriting', function() {
+		assert.deepEqual(
+			merge({a: 'b'}, {a: 'c'}),
+			{a: 'c'}
+    );
+	});
+
+	it('should merge take last patch attributes for rewriting and keep other attributes', function() {
+		assert.deepEqual(
+			merge({a: 'b', b: 'd'}, {a: 'c'}),
+			{a: 'c', b: 'd'}
+    );
+	});
+
+	it('should keep null attributes for deleting', function() {
+		assert.deepEqual(
+			merge({a: null}, {b: 'c'}),
+			{a: null, b: 'c'}
+    );
+	});
+
+	it('should replace null with newer attribute', function() {
+		assert.deepEqual(
+			merge({a: null}, {a: 'b'}),
+			{a: 'b'}
+		);
+	});
+
+	it('should replace an attribute with null if newer', function() {
+		assert.deepEqual(
+			merge({a: 'b'}, {a: null}),
+			{a: null}
+		);
+	});
+
+	it('should replace an array with an object', function() {
+		assert.deepEqual(
+			merge([], {a: 'b'}),
+			{a: 'b'}
+		);
+	});
+
+	it('should replace an object with an array', function() {
+		assert.deepEqual(
+			merge({a: 'b'}, []),
+			[]
+		);
+	});
+
+	it('should merge sub objects', function() {
+		assert.deepEqual(
+			merge({a: {b: {c: 'd'}}, d: 'e'}, {a: {b: 'a'}}),
+			{a: {b: 'a'}, d: 'e'}
+		);
+	});
+
+	it('should merge recursively', function() {
+		assert.deepEqual(
+			merge({a: {b: {c: 'd'}, d: 'e'}}, {a: {b: {c: 'e'}}}),
+			{a: {b: {c: 'e'}, d: 'e'}}
+		);
+	});
+
+	it('should replace object with with null value', function() {
+		assert.deepEqual(
+			merge({a: 'b'}, null),
+			null
+		);
+	});
+});