From 8c953dbc69ef4f9cdebf95a574a5e8fa6b0813ee Mon Sep 17 00:00:00 2001
From: bekzod <bekzod@me.com>
Date: Tue, 18 Jul 2017 01:50:04 +0500
Subject: [PATCH] handle negative index cases

---
 packages/ember-runtime/lib/mixins/array.js    | 20 +++++++++--------
 .../tests/suites/mutable_array/replace.js     | 22 +++++++++++++++++++
 2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/packages/ember-runtime/lib/mixins/array.js b/packages/ember-runtime/lib/mixins/array.js
index 4beafe4a098..9d931333bd0 100644
--- a/packages/ember-runtime/lib/mixins/array.js
+++ b/packages/ember-runtime/lib/mixins/array.js
@@ -142,20 +142,22 @@ export function arrayContentDidChange(array, startIdx, removeAmt, addAmt) {
   let meta = peekMeta(array);
   let cache = meta && meta.readableCache();
   if (cache !== undefined) {
-    if (cache.firstObject !== undefined && startIdx === 0) {
+    let length = get(array, 'length');
+    let addedAmount = (addAmt === -1 ? 0 : addAmt);
+    let removedAmount = (removeAmt === -1 ? 0 : removeAmt);
+    let delta = addedAmount - removedAmount;
+    let previousLength = length - delta;
+
+    let normalStartIdx = startIdx < 0 ? previousLength + startIdx : startIdx;
+    if (cache.firstObject !== undefined && normalStartIdx === 0) {
       propertyWillChange(array, 'firstObject');
       propertyDidChange(array, 'firstObject');
     }
 
     if (cache.lastObject !== undefined) {
-      let addedAmount = (addAmt === -1 ? 0 : addAmt);
-      let removedAmount = (removeAmt === -1 ? 0 : removeAmt);
-      let delta = addedAmount - removedAmount;
-      let length = get(array, 'length');
-
-      let lastIndex = length - delta - 1;
-      let lastAffectedIndex = startIdx + removedAmount;
-      if (lastIndex < lastAffectedIndex) {
+      let previousLastIndex = previousLength - 1;
+      let lastAffectedIndex = normalStartIdx + removedAmount;
+      if (previousLastIndex < lastAffectedIndex) {
         propertyWillChange(array, 'lastObject');
         propertyDidChange(array, 'lastObject');
       }
diff --git a/packages/ember-runtime/tests/suites/mutable_array/replace.js b/packages/ember-runtime/tests/suites/mutable_array/replace.js
index b9f17b08484..7823f510cb2 100644
--- a/packages/ember-runtime/tests/suites/mutable_array/replace.js
+++ b/packages/ember-runtime/tests/suites/mutable_array/replace.js
@@ -126,6 +126,28 @@ suite.test('[A,B,C,D].replace(2,2) => [A,B] + notify', function() {
   equal(observer.validate('firstObject'), false, 'should NOT have notified firstObject once');
 });
 
+suite.test('[A,B,C,D].replace(-1,1) => [A,B,C] + notify', function() {
+  let before  = this.newFixture(4);
+  let after   = [before[0], before[1], before[2]];
+
+  let obj = this.newObject(before);
+  let observer = this.newObserver(obj, '[]', '@each', 'length', 'firstObject', 'lastObject');
+
+  obj.getProperties('firstObject', 'lastObject'); /* Prime the cache */
+
+  obj.replace(-1, 1);
+
+  deepEqual(this.toArray(obj), after, 'post item results');
+
+  equal(observer.timesCalled('[]'), 1, 'should have notified [] once');
+  equal(observer.timesCalled('@each'), 0, 'should not have notified @each once');
+  equal(observer.timesCalled('length'), 1, 'should have notified length once');
+  equal(observer.timesCalled('lastObject'), 1, 'should have notified lastObject once');
+
+  equal(observer.validate('firstObject'), false, 'should NOT have notified firstObject once');
+});
+
+
 suite.test('Adding object should notify enumerable observer', function() {
   let fixtures = this.newFixture(4);
   let obj = this.newObject(fixtures);