From f4616d82babba896199f1a8a5aa7c007febb1026 Mon Sep 17 00:00:00 2001
From: Anton Platonov <platosha@gmail.com>
Date: Fri, 25 Aug 2017 17:56:31 +0300
Subject: [PATCH] Keyboard navigation: fix horizontal scrolling

---
 vaadin-grid-keyboard-navigation-mixin.html | 54 +++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/vaadin-grid-keyboard-navigation-mixin.html b/vaadin-grid-keyboard-navigation-mixin.html
index 88f83fce2..e35814573 100644
--- a/vaadin-grid-keyboard-navigation-mixin.html
+++ b/vaadin-grid-keyboard-navigation-mixin.html
@@ -41,6 +41,13 @@
       this.addEventListener('focusin', this._onFocusIn);
       this.addEventListener('focusout', this._onFocusOut);
       this.addEventListener('cell-focus', this._onCellFocus);
+
+      // Ensure horizontal scrolling when cell is focused, e.g., on tab key
+      this.$.table.addEventListener('focusin', (e) => {
+        if (e.composedPath().indexOf(this.$.table) === 3) {
+          this._scrollHorizontallyToCell(e.composedPath()[0]);
+        }
+      });
     }
 
     _focusableChanged(focusable, oldFocusable) {
@@ -211,13 +218,14 @@
           dstRowIndex === rowIndex &&
           dstIsRowDetails === isRowDetails) {
         // Navigation resulted in the same place, no action.
+        this._scrollHorizontallyToCell(activeCell);
         return;
       } else if (dstOrderedColumnIndex !== orderedColumnIndex) {
         // Horizontal movement invalidates stored _focusedColumnOrder
         this._focusedColumnOrder = undefined;
       }
 
-      // Ensure correct scroll position, destination row is visible
+      // Ensure correct vertical scroll position, destination row is visible
       if (activeRowGroup === this.$.items) {
         if (dstRowIndex <= this.firstVisibleIndex) {
           // Scroll up
@@ -242,6 +250,7 @@
         Array.from(dstRow.children)
           .filter(el => el.matches('[part~="details-cell"]'))[0] :
         dstRow.children[dstColumnIndex];
+      this._scrollHorizontallyToCell(dstCell);
       this._focusCell(dstCell, activeRowGroup);
     }
 
@@ -403,5 +412,48 @@
       }
       cell.focus();
     }
+
+    _scrollHorizontallyToCell(dstCell) {
+      if (dstCell.hasAttribute('frozen') || dstCell.matches('[part~="details-cell"]')) {
+        // These cells are, by design, always visible, no need to scroll.
+        return;
+      }
+
+      const dstCellRect = dstCell.getBoundingClientRect();
+      const dstRow = dstCell.parentNode;
+      const dstCellIndex = Array.from(dstRow.children).indexOf(dstCell);
+      const tableRect = this.$.table.getBoundingClientRect();
+      let leftBoundary = tableRect.left,
+          rightBoundary = tableRect.right;
+      for (let i = dstCellIndex - 1; i >= 0; i--) {
+        const cell = dstRow.children[i];
+        if (cell.hasAttribute('hidden') ||
+            cell.matches('[part~="details-cell"]')) {
+          continue;
+        }
+        if (cell.hasAttribute('frozen')) {
+          leftBoundary = cell.getBoundingClientRect().right;
+          break;
+        }
+      }
+      for (let i = dstCellIndex + 1; i < dstRow.children.length; i++) {
+        const cell = dstRow.children[i];
+        if (cell.hasAttribute('hidden') ||
+            cell.matches('[part~="details-cell"]')) {
+          continue;
+        }
+        if (cell.hasAttribute('frozen')) {
+          rightBoundary = cell.getBoundingClientRect().left;
+          break;
+        }
+      }
+
+      if (dstCellRect.left < leftBoundary) {
+        this.$.table.scrollLeft += Math.round(dstCellRect.left - leftBoundary);
+      }
+      if (dstCellRect.right > rightBoundary) {
+        this.$.table.scrollLeft += Math.round(dstCellRect.right - rightBoundary);
+      }
+    }
   };
 </script>