Fix latestMessageIndex out of bounds error

app/src/main/kotlin/dev/chungjungsoo/gptmobile/presentation/ui/chat/ChatScreen.kt

@@ -64,6 +64,7 @@ import androidx.hilt.navigation.compose.hiltViewModel
 import dev.chungjungsoo.gptmobile.R
 import dev.chungjungsoo.gptmobile.data.database.entity.Message
 import dev.chungjungsoo.gptmobile.data.model.ApiType
+import dev.chungjungsoo.gptmobile.util.DefaultHashMap
 import dev.chungjungsoo.gptmobile.util.collectManagedState
 import dev.chungjungsoo.gptmobile.util.multiScrollStateSaver
 import kotlinx.coroutines.delay
@@ -104,21 +105,10 @@ fun ChatScreen(
     val canUseChat = (chatViewModel.enabledPlatformsInChat.toSet() - appEnabledPlatforms.toSet()).isEmpty()
     val groupedMessages = remember(messages) { groupMessages(messages) }
     val latestMessageIndex = groupedMessages.keys.maxOrNull() ?: 0
-    val chatBubbleScrollStates = rememberSaveable(saver = multiScrollStateSaver) { MutableList(latestMessageIndex + 2) { ScrollState(0) } }
+    val chatBubbleScrollStates = rememberSaveable(saver = multiScrollStateSaver) { DefaultHashMap<Int, ScrollState>({ ScrollState(0) }) }
 
     val scope = rememberCoroutineScope()
 
-    LaunchedEffect(latestMessageIndex) {
-        val opponentBubbles = ((latestMessageIndex + 1) / 2) + 1
-        val scrollStatesToAdd = opponentBubbles - chatBubbleScrollStates.size
-
-        if (scrollStatesToAdd > 0) {
-            repeat(scrollStatesToAdd) {
-                chatBubbleScrollStates.add(ScrollState(0))
-            }
-        }
-    }
-
     LaunchedEffect(isIdle) {
         listState.animateScrollToItem(groupedMessages.keys.size)
     }

app/src/main/kotlin/dev/chungjungsoo/gptmobile/util/DefaultHashMap.kt

@@ -0,0 +1,18 @@
+package dev.chungjungsoo.gptmobile.util
+
+/**
+ Small implementation of HashMap, but with default values.
+ This way the get operator will not throw an error or null.
+ Inspired by Python collections DefaultDict.
+ */
+open class DefaultHashMap<K, V>(protected val defaultValueProvider: () -> V) : HashMap<K, V>() {
+    override operator fun get(key: K): V {
+        if (key in this) {
+            return super.get(key)!!
+        }
+
+        val defaultValue = defaultValueProvider()
+        this[key] = defaultValue
+        return super.get(key)!!
+    }
+}

app/src/main/kotlin/dev/chungjungsoo/gptmobile/util/ScrollStateSaver.kt

@@ -3,7 +3,15 @@ package dev.chungjungsoo.gptmobile.util
 import androidx.compose.foundation.ScrollState
 import androidx.compose.runtime.saveable.Saver
 
-val multiScrollStateSaver: Saver<MutableList<ScrollState>, *> = Saver(
-    save = { it.map { scrollState -> scrollState.value } },
-    restore = { it.map { i -> ScrollState(i) }.toMutableList() }
+val multiScrollStateSaver: Saver<DefaultHashMap<Int, ScrollState>, *> = Saver(
+    save = {
+        val saver = hashMapOf<Int, Int>()
+        it.forEach { i, scrollState -> saver[i] = scrollState.value }
+        saver
+    },
+    restore = {
+        val restored = DefaultHashMap<Int, ScrollState>({ ScrollState(0) })
+        it.forEach { i, v -> restored[i] = ScrollState(v) }
+        restored
+    }
 )