Optimize Notifcation loading

app/src/main/java/sh/sar/basedbank/ui/home/NotificationsSheetFragment.kt

@@ -13,10 +13,12 @@ import android.view.ViewGroup
 import android.widget.FrameLayout
 import android.widget.ImageView
 import android.widget.LinearLayout
+import android.widget.ProgressBar
 import android.widget.TextView
 import android.widget.Toast
 import androidx.core.view.isVisible
 import androidx.lifecycle.lifecycleScope
+import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.LinearLayoutManager
 import androidx.recyclerview.widget.RecyclerView
 import androidx.viewpager2.widget.ViewPager2
@@ -62,6 +64,23 @@ private fun toGroupedList(notifications: List<AppNotification>): List<NotifListI
     return result
 }
 
+private class NotifDiff(
+    private val old: List<NotifListItem>,
+    private val new: List<NotifListItem>
+) : DiffUtil.Callback() {
+    override fun getOldListSize() = old.size
+    override fun getNewListSize() = new.size
+    override fun areItemsTheSame(oldPos: Int, newPos: Int): Boolean {
+        val o = old[oldPos]; val n = new[newPos]
+        return when {
+            o is NotifListItem.Header && n is NotifListItem.Header -> o.label == n.label
+            o is NotifListItem.Entry  && n is NotifListItem.Entry  -> o.n.id == n.n.id
+            else -> false
+        }
+    }
+    override fun areContentsTheSame(oldPos: Int, newPos: Int) = old[oldPos] == new[newPos]
+}
+
 class NotificationsSheetFragment : BottomSheetDialogFragment() {
 
     var onUnreadCountChanged: ((hasUnread: Boolean) -> Unit)? = null
@@ -148,11 +167,16 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
         }
     }
 
+    private fun setSpinner(show: Boolean) {
+        tabAdapters.forEach { it?.showLoadingSpinner = show }
+    }
+
     private fun refreshFromNetwork() {
         val bmlSessions = app.bmlSessions.toMap()
         val mibSessions = app.mibSessions.toMap()
 
         lifecycleScope.launch {
+            setSpinner(true)
             val bmlClient = BmlNotificationsClient()
             bmlSessions.forEach { (loginId, session) ->
                 val result = withContext(Dispatchers.IO) {
@@ -196,6 +220,8 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
                     mibDone[loginId] = hasOverlap || result.nextStart > result.totalCount
                 }
             }
+
+            if (isAdded) setSpinner(false)
         }
     }
 
@@ -208,6 +234,7 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
         if (!anyLeft) return
 
         isLoadingMore = true
+        setSpinner(true)
         lifecycleScope.launch {
             val bmlClient = BmlNotificationsClient()
             bmlSessions.forEach { (loginId, session) ->
@@ -255,7 +282,10 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
             }
 
             isLoadingMore = false
-            if (isAdded) refreshAdapters()
+            if (isAdded) {
+                setSpinner(false)
+                refreshAdapters()
+            }
         }
     }
 
@@ -359,16 +389,35 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
 
         private val displayItems = mutableListOf<NotifListItem>()
 
+        var showLoadingSpinner: Boolean = false
+            set(value) {
+                if (field == value) return
+                field = value
+                if (displayItems.isEmpty()) {
+                    notifyItemChanged(0)
+                } else if (value) {
+                    notifyItemInserted(displayItems.size)
+                } else {
+                    notifyItemRemoved(displayItems.size)
+                }
+            }
+
         fun update(filtered: List<AppNotification>) {
+            val newItems = toGroupedList(filtered)
+            val diff = DiffUtil.calculateDiff(NotifDiff(displayItems.toList(), newItems))
             displayItems.clear()
-            displayItems.addAll(toGroupedList(filtered))
-            notifyDataSetChanged()
+            displayItems.addAll(newItems)
+            diff.dispatchUpdatesTo(this)
         }
 
-        override fun getItemCount() = if (displayItems.isEmpty()) 1 else displayItems.size
+        override fun getItemCount(): Int {
+            if (displayItems.isEmpty()) return 1
+            return displayItems.size + if (showLoadingSpinner) 1 else 0
+        }
 
         override fun getItemViewType(position: Int): Int {
-            if (displayItems.isEmpty()) return 2 // empty
+            if (displayItems.isEmpty()) return if (showLoadingSpinner) 3 else 2
+            if (showLoadingSpinner && position == displayItems.size) return 3
             return when (displayItems[position]) {
                 is NotifListItem.Header -> 0
                 is NotifListItem.Entry  -> 1
@@ -379,6 +428,7 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
             when (viewType) {
                 0    -> HeaderVH(buildHeaderView(parent.context))
                 1    -> ItemVH(buildRowView(parent.context))
+                3    -> SpinnerVH(buildSpinnerView(parent.context))
                 else -> EmptyVH(buildEmptyView(parent.context))
             }
 
@@ -439,6 +489,28 @@ class NotificationsSheetFragment : BottomSheetDialogFragment() {
             }
         }
 
+        // ── Loading spinner ───────────────────────────────────────────────────────
+
+        inner class SpinnerVH(v: View) : RecyclerView.ViewHolder(v)
+
+        private fun buildSpinnerView(ctx: android.content.Context): View {
+            val dp = ctx.resources.displayMetrics.density
+            val pad = (16 * dp).toInt()
+            val size = (28 * dp).toInt()
+            return LinearLayout(ctx).apply {
+                orientation = LinearLayout.VERTICAL
+                gravity = Gravity.CENTER
+                layoutParams = ViewGroup.LayoutParams(
+                    ViewGroup.LayoutParams.MATCH_PARENT,
+                    ViewGroup.LayoutParams.WRAP_CONTENT
+                )
+                setPadding(pad, pad, pad, pad)
+                addView(ProgressBar(ctx).apply {
+                    layoutParams = LinearLayout.LayoutParams(size, size)
+                })
+            }
+        }
+
         // ── Notification row ──────────────────────────────────────────────────────
 
         inner class ItemVH(v: View) : RecyclerView.ViewHolder(v) {