added prepareInstancePositionChanged delegate method

[email protected], arv
BUG=

Review URL: https://codereview.appspot.com/14743044

src/TemplateBinding.js

@@ -1001,6 +1001,14 @@
       return instanceNodes;
     },
 
+    getDelegateFunction: function(delegate, name, template) {
+      if (!delegate || typeof delegate[name] !== 'function')
+        return null;
+
+      var fn = delegate[name](template);
+      return typeof fn === 'function' ? fn : null;
+    },
+
     handleSplices: function(splices) {
       if (this.closed)
         return;
@@ -1014,10 +1022,15 @@
       }
 
       if (this.instanceModelFn_ === undefined) {
-        if (delegate && typeof delegate.prepareInstanceModel === 'function')
-          this.instanceModelFn_ = delegate.prepareInstanceModel(template);
-        if (typeof this.instanceModelFn_ !== 'function')
-          this.instanceModelFn_ = false;
+        this.instanceModelFn_ = this.getDelegateFunction(delegate,
+                                                         'prepareInstanceModel',
+                                                         template);
+      }
+
+      if (this.instancePositionChangedFn_ === undefined) {
+        this.instancePositionChangedFn_ =
+            this.getDelegateFunction(delegate, 'prepareInstancePositionChanged',
+                                     template);
       }
 
       var instanceCache = new Map;
@@ -1061,6 +1074,55 @@
       instanceCache.forEach(function(instanceNodes) {
         this.closeInstanceBindings(instanceNodes.bound);
       }, this);
+
+      if (this.instancePositionChangedFn_)
+        this.reportInstancesMoved(splices);
+    },
+
+    reportInstanceMoved: function(index) {
+      var previousTerminator = this.getTerminatorAt(index - 1);
+      var terminator = this.getTerminatorAt(index);
+      if (previousTerminator === terminator)
+        return; // instance has zero nodes.
+
+      // We must use the first node of the instance, because any subsequent
+      // nodes may have been generated by sub-templates.
+      // TODO(rafaelw): This is brittle WRT instance mutation -- e.g. if the
+      // first node was removed by script.
+      var templateInstance = previousTerminator.nextSibling.templateInstance;
+      this.instancePositionChangedFn_(templateInstance, index);
+    },
+
+    reportInstancesMoved: function(splices) {
+      var index = 0;
+      var offset = 0;
+      for (var i = 0; i < splices.length; i++) {
+        var splice = splices[i];
+        if (offset != 0) {
+          while (index < splice.index) {
+            this.reportInstanceMoved(index);
+            index++;
+          }
+        } else {
+          index = splice.index;
+        }
+
+        while (index < splice.index + splice.addedCount) {
+          this.reportInstanceMoved(index);
+          index++;
+        }
+
+        offset += splice.addedCount - splice.removed.length;
+      }
+
+      if (offset == 0)
+        return;
+
+      var length = this.terminators.length / 2;
+      while (index < length) {
+        this.reportInstanceMoved(index);
+        index++;
+      }
     },
 
     closeInstanceBindings: function(bound) {

tests/tests.js

@@ -1859,7 +1859,7 @@ suite('Template Instantiation', function() {
 
     var template = div.firstChild;
 
-    var model = { 
+    var model = {
       show: true,
       items: [1]
     };
@@ -1890,7 +1890,7 @@ suite('Binding Delegate API', function() {
 
   teardown(doTeardown);
 
-  test('Registration', function() {
+  test('prepareBinding', function() {
     var model = { foo: 'bar'};
     var prepareBindData = {
       type: 'prepare',
@@ -1967,7 +1967,7 @@ suite('Binding Delegate API', function() {
     assert.strictEqual(0, testData.length);
   });
 
-  test('getInstanceModel', function() {
+  test('prepareInstanceModel', function() {
     var model = [{ foo: 1 }, { foo: 2 }, { foo: 3 }];
 
     var div = createTestHtml(
@@ -2017,7 +2017,7 @@ suite('Binding Delegate API', function() {
     assert.strictEqual(0, testData.length);
   });
 
-  test('getInstanceModel - reorder instances', function() {
+  test('prepareInstanceModel - reorder instances', function() {
     var model = [0, 1, 2];
 
     var div = createTestHtml(
@@ -2048,6 +2048,64 @@ suite('Binding Delegate API', function() {
     assert.strictEqual(3, callCount);
   });
 
+  test('prepareInstancePositionChanged', function() {
+    var model = ['a', 'b', 'c'];
+
+    var div = createTestHtml(
+        '<template repeat>' +
+        '{{}}</template>');
+    var template = div.firstChild;
+
+    var testData = [
+      {
+        template: template,
+      },
+      {
+        model: model[0],
+        index: 0
+      },
+      {
+        model: model[1],
+        index: 1
+      },
+      {
+        model: model[2],
+        index: 2
+      },
+      // After splice
+      {
+        model: model[2],
+        index: 1
+      }
+    ];
+
+    var delegate = {
+      prepareInstancePositionChanged: function(template) {
+        var data = testData.shift();
+        assert.strictEqual(data.template, template);
+
+        return function(templateInstance, index) {
+          data = testData.shift();
+          assert.strictEqual(data.model, templateInstance.model);
+          assert.strictEqual(data.index, index);
+        }
+      }
+    };
+
+    recursivelySetTemplateModel(div, model, delegate);
+    Platform.performMicrotaskCheckpoint();
+    assert.strictEqual(4, div.childNodes.length);
+    assert.strictEqual('TEMPLATE', div.childNodes[0].tagName);
+    assert.strictEqual('a', div.childNodes[1].textContent);
+    assert.strictEqual('b', div.childNodes[2].textContent);
+    assert.strictEqual('c', div.childNodes[3].textContent);
+
+    model.splice(1, 1);
+    Platform.performMicrotaskCheckpoint();
+
+    assert.strictEqual(0, testData.length);
+  });
+
   test('Basic', function() {
     var model = { foo: 2, bar: 4 };