tuning min/max indicies during removing via Adapter

Author: dhilt

src/modules/adapter.js

@@ -158,10 +158,10 @@ class Adapter {
       if(angular.isArray(newItems) && !newItems.length) {
         var isTop = index === this.buffer.minIndex;
         if(isTop) {
-          this.buffer.minIndex++;
+          this.buffer.incrementMinIndex();
         }
         else {
-          this.buffer.maxIndex--;
+          this.buffer.decrementMinIndex();
         }
         this.viewport.removeCacheItem(index, isTop);
       }

src/modules/buffer.js

@@ -78,9 +78,15 @@ export default function ScrollBuffer(elementRoutines, bufferSize) {
       // removes single item(wrapper) from the buffer
       buffer.splice(buffer.indexOf(arg1), 1);
       if(arg1._op === 'isTop') {
+        if(buffer.first === buffer.minIndex) {
+          this.incrementMinIndex();
+        }
         buffer.first++;
       }
       else {
+        if(buffer.next === buffer.maxIndex + 1) {
+          this.decrementMinIndex();
+        }
         buffer.next--;
       }
       if(!buffer.length) {
@@ -91,6 +97,18 @@ export default function ScrollBuffer(elementRoutines, bufferSize) {
       return elementRoutines.removeElementAnimated(arg1);
     },
 
+    incrementMinIndex() {
+      if(buffer.minIndex++ === buffer.minIndexUser) {
+        buffer.minIndexUser++;
+      }
+    },
+
+    decrementMinIndex() {
+      if(buffer.maxIndex-- === buffer.maxIndexUser) {
+        buffer.maxIndexUser--;
+      }
+    },
+
     effectiveHeight(elements) {
       if (!elements.length) {
         return 0;