Navigate to next unreviewed file after moving to last diff chunk

Show toast to users telling them pressing n on the last diff chunk
of a file will navigate them to next unreviewed file.
Pressing n after displaying the toast does the navigation.

Change-Id: I8c1248b43ceb88cd464b8ab92eecb57e2d57b39d

polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor.js

@@ -202,9 +202,10 @@ class GrDiffCursor extends GestureEventListeners(
     }
   }
 
-  moveToNextChunk(opt_clipToTop) {
+  moveToNextChunk(opt_clipToTop, opt_navigateToNextFile) {
     this.$.cursorManager.next(this._isFirstRowOfChunk.bind(this),
-        target => target.parentNode.scrollHeight, opt_clipToTop);
+        target => target.parentNode.scrollHeight, opt_clipToTop,
+        opt_navigateToNextFile);
     this._fixSide();
   }
 

polygerrit-ui/app/elements/diff/gr-diff-cursor/gr-diff-cursor_test.html

@@ -244,6 +244,21 @@ suite('gr-diff-cursor tests', () => {
     assert.equal(cursorElement.side, 'left');
   });
 
+  test('navigate to next unreviewed file via moveToNextChunk', () => {
+    const cursor = cursorElement.shadowRoot.querySelector('#cursorManager');
+    cursor.index = cursor.stops.length - 1;
+    const dispatchEventStub = sandbox.stub(cursor, 'dispatchEvent');
+    cursorElement.moveToNextChunk(/* opt_clipToTop = */false,
+        /* opt_navigateToNextFile = */true);
+    assert.isTrue(dispatchEventStub.called);
+    assert.equal(dispatchEventStub.getCall(0).args[0].type, 'show-alert');
+
+    cursorElement.moveToNextChunk(/* opt_clipToTop = */false,
+        /* opt_navigateToNextFile = */true);
+    assert.equal(dispatchEventStub.getCall(1).args[0].type,
+        'navigate-to-next-unreviewed-file');
+  });
+
   test('initialLineNumber not provided', done => {
     let scrollBehaviorDuringMove;
     const moveToNumStub = sandbox.stub(cursorElement, 'moveToLineNumber');

polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.js

@@ -556,7 +556,8 @@ class GrDiffView extends mixinBehaviors( [
       this.$.cursor.moveToNextCommentThread();
     } else {
       if (this.modifierPressed(e)) { return; }
-      this.$.cursor.moveToNextChunk();
+      this.$.cursor.moveToNextChunk(/* opt_clipToTop = */false,
+          /* opt_navigateToNextFile = */true);
     }
   }
 

polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_html.js

@@ -422,6 +422,7 @@ export const htmlTemplate = html`
   <gr-diff-cursor
     id="cursor"
     scroll-top-margin="[[_scrollTopMargin]]"
+    on-navigate-to-next-unreviewed-file="_handleNextUnreviewedFile"
   ></gr-diff-cursor>
   <gr-comment-api id="commentAPI"></gr-comment-api>
 `;

polygerrit-ui/app/elements/shared/gr-cursor-manager/gr-cursor-manager.js

@@ -119,11 +119,15 @@ class GrCursorManager extends GestureEventListeners(
    *    sometimes different, used by the diff cursor.
    * @param {boolean=} opt_clipToTop When none of the next indices match, move
    *     back to first instead of to last.
+   * @param {boolean=} opt_navigateToNextFile Navigate to next unreviewed file
+   *     if user presses next on the last diff chunk
    * @private
    */
 
-  next(opt_condition, opt_getTargetHeight, opt_clipToTop) {
-    this._moveCursor(1, opt_condition, opt_getTargetHeight, opt_clipToTop);
+  next(opt_condition, opt_getTargetHeight, opt_clipToTop,
+      opt_navigateToNextFile) {
+    this._moveCursor(1, opt_condition, opt_getTargetHeight, opt_clipToTop,
+        opt_navigateToNextFile);
   }
 
   previous(opt_condition) {
@@ -265,9 +269,12 @@ class GrCursorManager extends GestureEventListeners(
    *    sometimes different, used by the diff cursor.
    * @param {boolean=} opt_clipToTop When none of the next indices match, move
    *     back to first instead of to last.
+   * @param {boolean=} opt_navigateToNextFile Navigate to next unreviewed file
+   *     if user presses next on the last diff chunk
    * @private
    */
-  _moveCursor(delta, opt_condition, opt_getTargetHeight, opt_clipToTop) {
+  _moveCursor(delta, opt_condition, opt_getTargetHeight, opt_clipToTop,
+      opt_navigateToNextFile) {
     if (!this.stops.length) {
       this.unsetCursor();
       return;
@@ -282,6 +289,32 @@ class GrCursorManager extends GestureEventListeners(
       newTarget = this.stops[newIndex];
     }
 
+    /*
+     * If user presses n on the last diff chunk, show a toast informing user
+     * that pressing n again will navigate them to next unreviewed file
+     */
+    if (opt_navigateToNextFile && this.index === newIndex) {
+      if (newIndex === this.stops.length - 1) {
+        if (this._displayedNavigateToNextFileToast) {
+          // reset for next file
+          this._displayedNavigateToNextFileToast = false;
+          this.dispatchEvent(new CustomEvent(
+              'navigate-to-next-unreviewed-file', {
+                composed: true, bubbles: true,
+              }));
+          return;
+        }
+        this._displayedNavigateToNextFileToast = true;
+        this.dispatchEvent(new CustomEvent('show-alert', {
+          detail: {
+            message: 'Press n again to navigate to next unreviewed file',
+          },
+          composed: true, bubbles: true,
+        }));
+        return;
+      }
+    }
+
     this.index = newIndex;
     this.target = newTarget;