[fenix] For https://github.com/mozilla-mobile/fenix/issues/15115 - Part 7: Draw a border around the selected tab

app/src/main/java/org/mozilla/fenix/tabtray/TabTrayGridItemDecorator.kt

@@ -0,0 +1,62 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix.tabtray
+
+import android.content.Context
+import android.graphics.Canvas
+import android.graphics.Paint
+import android.graphics.RectF
+import android.view.View
+import androidx.core.content.ContextCompat
+import androidx.recyclerview.widget.RecyclerView
+import org.mozilla.fenix.R
+import org.mozilla.fenix.ext.components
+
+/**
+ * An item decorator for the tab tray grid tabs. Draws a border for the selected tab.
+ */
+class TabTrayGridItemDecorator(context: Context) :
+    RecyclerView.ItemDecoration() {
+
+    override fun onDrawOver(canvas: Canvas, recyclerView: RecyclerView, state: RecyclerView.State) {
+        for (i in 0 until recyclerView.childCount) {
+            val child = recyclerView.getChildAt(i)
+            val viewHolder = recyclerView.getChildViewHolder(child)
+            if (viewHolder !is TabTrayViewHolder) {
+                continue
+            }
+
+            if (viewHolder.tab?.id == recyclerView.context.components.core.store.state.selectedTabId) {
+                drawSelectedTabBorder(child, canvas)
+            }
+        }
+
+        super.onDrawOver(canvas, recyclerView, state)
+    }
+
+    private fun drawSelectedTabBorder(child: View, canvas: Canvas) {
+        val borderRadius =
+            child.resources.getDimensionPixelSize(R.dimen.tab_tray_grid_item_border_radius)
+                .toFloat()
+        canvas.drawRoundRect(child.getBounds(), borderRadius, borderRadius, borderStroke)
+    }
+
+    private val borderStroke: Paint = Paint().apply {
+        color = ContextCompat.getColor(context, R.color.photonViolet50)
+        isAntiAlias = true
+        strokeWidth =
+            context.resources.getDimensionPixelSize(R.dimen.tab_tray_grid_item_selected_border_width)
+                .toFloat()
+        style = Paint.Style.STROKE
+    }
+
+    private fun View.getBounds(): RectF {
+        val leftPosition = left + translationX - paddingLeft
+        val rightPosition = right + translationX + paddingRight
+        val topPosition = top + translationY - paddingTop
+        val bottomPosition = bottom + translationY + paddingBottom
+        return RectF(leftPosition, topPosition, rightPosition, bottomPosition)
+    }
+}

app/src/main/java/org/mozilla/fenix/tabtray/TabTrayView.kt

@@ -335,6 +335,8 @@ class TabTrayView(
         updateUINormalMode(view.context.components.core.store.state)
         scrollToTab(view.context.components.core.store.state.selectedTabId)
 
+        view.tabsTray.invalidateItemDecorations()
+
         if (isPrivateModeSelected) {
             components.analytics.metrics.track(Event.TabsTrayPrivateModeTapped)
         } else {
@@ -373,6 +375,7 @@ class TabTrayView(
             }
 
             layoutManager = gridLayoutManager
+            addItemDecoration(TabTrayGridItemDecorator(container.context))
         }
     }