Flip chat-history row icon when selection toggles

Animate a 300ms Y-axis flip on the row's icon container when the user
toggles a row in or out of selection, swapping the chat-type drawable
and accent background at the apex. The flip runs only on selection
changes detected via DiffUtil.getChangePayload and routed through the
3-arg onBindViewHolder, so scrolling and full rebinds stay snappy.

Author: GerardPaligot

duckchat/duckchat-impl/src/main/java/com/duckduckgo/duckchat/impl/history/ChatHistoryAdapter.kt

@@ -58,6 +58,20 @@ class ChatHistoryAdapter(
         }
     }
 
+    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int, payloads: MutableList<Any>) {
+        val selectionChange = payloads.firstOrNull { it is RowChange.SelectionChanged } as? RowChange.SelectionChanged
+        val entry = getItem(position)
+        if (selectionChange != null && holder is ChatHistoryViewHolder && entry is ChatHistoryListEntry.Row) {
+            holder.animateSelectionChange(entry.item, selectionChange.selected)
+        } else {
+            onBindViewHolder(holder, position)
+        }
+    }
+
+    private sealed interface RowChange {
+        data class SelectionChanged(val selected: Boolean) : RowChange
+    }
+
     private object Diff : DiffUtil.ItemCallback<ChatHistoryListEntry>() {
         override fun areItemsTheSame(oldItem: ChatHistoryListEntry, newItem: ChatHistoryListEntry): Boolean = when {
             oldItem is ChatHistoryListEntry.Header && newItem is ChatHistoryListEntry.Header ->
@@ -70,6 +84,15 @@ class ChatHistoryAdapter(
 
         override fun areContentsTheSame(oldItem: ChatHistoryListEntry, newItem: ChatHistoryListEntry): Boolean =
             oldItem == newItem
+
+        override fun getChangePayload(oldItem: ChatHistoryListEntry, newItem: ChatHistoryListEntry): Any? {
+            if (oldItem is ChatHistoryListEntry.Row && newItem is ChatHistoryListEntry.Row &&
+                oldItem.item == newItem.item && oldItem.selected != newItem.selected
+            ) {
+                return RowChange.SelectionChanged(newItem.selected)
+            }
+            return null
+        }
     }
 
     private companion object {

duckchat/duckchat-impl/src/main/java/com/duckduckgo/duckchat/impl/history/ChatHistoryViewHolder.kt

@@ -19,6 +19,8 @@ package com.duckduckgo.duckchat.impl.history
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.view.animation.AccelerateInterpolator
+import android.view.animation.DecelerateInterpolator
 import android.widget.FrameLayout
 import android.widget.ImageView
 import androidx.recyclerview.widget.RecyclerView
@@ -41,7 +43,34 @@ class ChatHistoryViewHolder(
         onMoreClick: (ChatHistoryItem, View) -> Unit,
         onLongClick: (ChatHistoryItem) -> Boolean = { false },
     ) {
+        iconContainer.animate().cancel()
+        iconContainer.rotationY = 0f
         title.text = item.displayTitle
+        applySelectionState(item, selected)
+        itemView.setOnClickListener { onClick(item) }
+        itemView.setOnLongClickListener { onLongClick(item) }
+        moreButton.setOnClickListener { anchor -> onMoreClick(item, anchor) }
+    }
+
+    fun animateSelectionChange(item: ChatHistoryItem, selected: Boolean) {
+        iconContainer.animate().cancel()
+        iconContainer.animate()
+            .rotationY(HALF_FLIP_DEGREES)
+            .setDuration(HALF_FLIP_DURATION_MS)
+            .setInterpolator(AccelerateInterpolator())
+            .withEndAction {
+                applySelectionState(item, selected)
+                iconContainer.rotationY = -HALF_FLIP_DEGREES
+                iconContainer.animate()
+                    .rotationY(0f)
+                    .setDuration(HALF_FLIP_DURATION_MS)
+                    .setInterpolator(DecelerateInterpolator())
+                    .start()
+            }
+            .start()
+    }
+
+    private fun applySelectionState(item: ChatHistoryItem, selected: Boolean) {
         if (selected) {
             iconContainer.setBackgroundResource(R.drawable.bg_chat_history_circle_accent)
             typeIcon.setImageResource(com.duckduckgo.mobile.android.R.drawable.ic_check_24)
@@ -53,9 +82,6 @@ class ChatHistoryViewHolder(
             typeIcon.colorFilter = null
             iconContainer.contentDescription = null
         }
-        itemView.setOnClickListener { onClick(item) }
-        itemView.setOnLongClickListener { onLongClick(item) }
-        moreButton.setOnClickListener { anchor -> onMoreClick(item, anchor) }
     }
 
     private fun iconFor(type: ChatType, pinned: Boolean): Int = when (type) {
@@ -65,6 +91,9 @@ class ChatHistoryViewHolder(
     }
 
     companion object {
+        private const val HALF_FLIP_DEGREES = 90f
+        private const val HALF_FLIP_DURATION_MS = 150L
+
         fun create(parent: ViewGroup): ChatHistoryViewHolder {
             val view = LayoutInflater.from(parent.context)
                 .inflate(R.layout.view_chat_history_item, parent, false)