feat(comments): remember comment collapsed state

Remember the comment expanded/collapsed state when scrolling. Previously,
the state was remembered inside the `Node` composable. When the users scroll,
and `Node` re-composes, the state was being reset.

In this commit, we add the collapsed state into the `CommentNode`. This makes
sure that the state is retained even when the UI is re-composed.

common/src/main/kotlin/dev/msfjarvis/claw/common/comments/CommentNode.kt

@@ -6,15 +6,15 @@
  */
 package dev.msfjarvis.claw.common.comments
 
-import dev.msfjarvis.claw.database.local.PostComments
 import dev.msfjarvis.claw.model.Comment
 
-internal class CommentNode(
+internal data class CommentNode(
   val comment: Comment,
   private var parent: CommentNode? = null,
   val children: MutableList<CommentNode> = mutableListOf(),
   val isUnread: Boolean = false,
   val indentLevel: Int,
+  val isExpanded: Boolean = true,
 ) {
 
   fun addChild(child: CommentNode) {
@@ -50,6 +50,7 @@ internal class CommentNode(
     if (children != other.children) return false
     if (isUnread != other.isUnread) return false
     if (indentLevel != other.indentLevel) return false
+    if (isExpanded != other.isExpanded) return false
 
     return true
   }
@@ -59,37 +60,7 @@ internal class CommentNode(
     result = 31 * result + children.hashCode()
     result = 31 * result + isUnread.hashCode()
     result = 31 * result + indentLevel
+    result = 31 * result + isExpanded.hashCode()
     return result
   }
 }
-
-internal fun createListNode(
-  comments: List<Comment>,
-  commentState: PostComments?,
-): MutableList<CommentNode> {
-  val commentNodes = mutableListOf<CommentNode>()
-  val isUnread = { id: String -> commentState?.commentIds?.contains(id) == false }
-
-  for (i in comments.indices) {
-    if (comments[i].parentComment == null) {
-      commentNodes.add(
-        CommentNode(
-          comment = comments[i],
-          isUnread = isUnread(comments[i].shortId),
-          indentLevel = 1,
-        )
-      )
-    } else {
-      commentNodes.lastOrNull()?.let { commentNode ->
-        commentNode.addChild(
-          CommentNode(
-            comment = comments[i],
-            isUnread = isUnread(comments[i].shortId),
-            indentLevel = commentNode.indentLevel + 1,
-          )
-        )
-      }
-    }
-  }
-  return commentNodes
-}

common/src/main/kotlin/dev/msfjarvis/claw/common/comments/CommentsHandler.kt

@@ -0,0 +1,60 @@
+/*
+ * Copyright © 2024 Harsh Shandilya.
+ * Use of this source code is governed by an MIT-style
+ * license that can be found in the LICENSE file or at
+ * https://opensource.org/licenses/MIT.
+ */
+package dev.msfjarvis.claw.common.comments
+
+import dev.msfjarvis.claw.database.local.PostComments
+import dev.msfjarvis.claw.model.Comment
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+
+internal class CommentsHandler {
+
+  private val _listItems: MutableStateFlow<List<CommentNode>> = MutableStateFlow(emptyList())
+  val listItems: StateFlow<List<CommentNode>> = _listItems.asStateFlow()
+
+  fun createListNode(comments: List<Comment>, commentState: PostComments?) {
+    val commentNodes = mutableListOf<CommentNode>()
+    val isUnread = { id: String -> commentState?.commentIds?.contains(id) == false }
+
+    for (i in comments.indices) {
+      if (comments[i].parentComment == null) {
+        commentNodes.add(
+          CommentNode(
+            comment = comments[i],
+            isUnread = isUnread(comments[i].shortId),
+            indentLevel = 1,
+          )
+        )
+      } else {
+        commentNodes.lastOrNull()?.let { commentNode ->
+          commentNode.addChild(
+            CommentNode(
+              comment = comments[i],
+              isUnread = isUnread(comments[i].shortId),
+              indentLevel = commentNode.indentLevel + 1,
+            )
+          )
+        }
+      }
+    }
+
+    _listItems.value = commentNodes
+  }
+
+  fun updateListNode(shortId: String, isExpanded: Boolean) {
+    val listNode = _listItems.value.toMutableList()
+    val index = listNode.indexOfFirst { it.comment.shortId == shortId }
+
+    if (index != -1) {
+      val commentNode = listNode[index].copy(isExpanded = isExpanded)
+      listNode[index] = commentNode
+
+      _listItems.value = listNode.toList()
+    }
+  }
+}

common/src/main/kotlin/dev/msfjarvis/claw/common/comments/CommentsPage.kt

@@ -60,6 +60,7 @@ fun CommentsPage(
         markSeenComments = markSeenComments,
         openUserProfile = openUserProfile,
         contentPadding = contentPadding,
+        commentsHandler = CommentsHandler(),
         modifier = modifier.fillMaxSize(),
       )
     }

common/src/main/kotlin/dev/msfjarvis/claw/common/comments/CommentsPageImpl.kt

@@ -8,6 +8,12 @@ package dev.msfjarvis.claw.common.comments
 
 import android.text.format.DateUtils
 import android.widget.Toast
+import androidx.compose.animation.AnimatedVisibility
+import androidx.compose.animation.core.tween
+import androidx.compose.animation.expandVertically
+import androidx.compose.animation.fadeIn
+import androidx.compose.animation.fadeOut
+import androidx.compose.animation.shrinkVertically
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
@@ -21,6 +27,7 @@ import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.systemBars
 import androidx.compose.foundation.layout.windowInsetsBottomHeight
 import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
@@ -28,9 +35,6 @@ import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.mutableStateOf
-import androidx.compose.runtime.remember
-import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
@@ -39,6 +43,7 @@ import androidx.compose.ui.text.buildAnnotatedString
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import dev.msfjarvis.claw.common.posts.PostActions
 import dev.msfjarvis.claw.common.posts.Submitter
 import dev.msfjarvis.claw.common.ui.ThemedRichText
@@ -48,6 +53,8 @@ import dev.msfjarvis.claw.model.UIPost
 import java.time.Instant
 import java.time.temporal.TemporalAccessor
 
+private const val AnimationDuration = 100
+
 @Composable
 internal fun CommentsPageInternal(
   details: UIPost,
@@ -57,10 +64,19 @@ internal fun CommentsPageInternal(
   markSeenComments: (String, List<Comment>) -> Unit,
   openUserProfile: (String) -> Unit,
   contentPadding: PaddingValues,
+  commentsHandler: CommentsHandler,
   modifier: Modifier = Modifier,
 ) {
+
+  LaunchedEffect(Unit) { commentsHandler.createListNode(details.comments, commentState) }
+
+  val onToggleExpandedState = { shortId: String, isExpanded: Boolean ->
+    commentsHandler.updateListNode(shortId, isExpanded)
+  }
+
   val context = LocalContext.current
-  val commentNodes = createListNode(details.comments, commentState)
+  val commentNodes by commentsHandler.listItems.collectAsStateWithLifecycle()
+
   LaunchedEffect(key1 = commentNodes) {
     if (details.comments.isNotEmpty() && !commentState?.commentIds.isNullOrEmpty()) {
       val unreadCount = details.comments.size - (commentState?.commentIds?.size ?: 0)
@@ -96,8 +112,8 @@ internal fun CommentsPageInternal(
           )
         }
 
-        commentNodes.forEach { node ->
-          item(key = node.comment.shortId) { Node(node, htmlConverter, openUserProfile) }
+        items(items = commentNodes, key = { node -> node.comment.shortId }) { node ->
+          Node(node, htmlConverter, openUserProfile, onToggleExpandedState)
         }
 
         item(key = "bottom_spacer") {
@@ -127,22 +143,30 @@ private fun Node(
   node: CommentNode,
   htmlConverter: HTMLConverter,
   openUserProfile: (String) -> Unit,
+  onToggleExpandedState: (String, Boolean) -> Unit,
   modifier: Modifier = Modifier,
 ) {
   Column(horizontalAlignment = Alignment.CenterHorizontally) {
-    var isChildrenShown by remember { mutableStateOf(true) }
-
     NodeBox(
       node = node,
-      isExpanded = isChildrenShown,
+      isExpanded = node.isExpanded,
       htmlConverter = htmlConverter,
       openUserProfile,
-      modifier = modifier.clickable(onClick = { isChildrenShown = !isChildrenShown }),
+      modifier =
+        modifier.clickable(
+          onClick = { onToggleExpandedState(node.comment.shortId, !node.isExpanded) }
+        ),
     )
 
-    if (isChildrenShown) {
+    AnimatedVisibility(
+      visible = node.isExpanded,
+      enter = fadeIn(tween(AnimationDuration)) + expandVertically(tween(AnimationDuration)),
+      exit = fadeOut(tween(AnimationDuration)) + shrinkVertically(tween(AnimationDuration)),
+    ) {
       Column(modifier = modifier, horizontalAlignment = Alignment.CenterHorizontally) {
-        node.children.forEach { model -> Node(model, htmlConverter, openUserProfile) }
+        node.children.forEach { model ->
+          Node(model, htmlConverter, openUserProfile, onToggleExpandedState)
+        }
       }
     }
   }