fix(emoji): grey out the backspace button when there is nothing to delete

EmojiPickerPanel gains backspaceActionAvailable, which the host toggles
independently of backspaceEnabled (which only controls whether the
button shows at all). MessageInputFragment now keeps it in sync with
whether the message input actually has text, since the panel itself
has no knowledge of the host's text field content.

Assisted-by: Claude Code:claude-sonnet-5

Signed-off-by: Marcel Hibbe <dev@mhibbe.de>

Author: mahibi

app/src/main/java/com/nextcloud/talk/chat/MessageInputFragment.kt

@@ -468,6 +468,7 @@ class MessageInputFragment : Fragment() {
                 val text = binding.fragmentMessageInputView.messageInput.text.toString()
                 chatActivity.chatViewModel.messageDraft.messageCursor = cursor
                 chatActivity.chatViewModel.messageDraft.messageText = text
+                binding.emojiPickerPanel.backspaceActionAvailable = s.isNotEmpty()
                 handleButtonsVisibility()
             }
         })
@@ -893,6 +894,7 @@ class MessageInputFragment : Fragment() {
         emojiPickerPanel.setRecentEmojiProvider(recentEmojiProvider)
         emojiPickerPanel.onEmojiPicked = { emoji -> insertEmoji(emoji) }
         emojiPickerPanel.onBackspaceClicked = { deleteEmojiOrCharacterBeforeCursor() }
+        emojiPickerPanel.backspaceActionAvailable = inputEditText.text?.isNotEmpty() == true
 
         viewThemeUtils.talk.themeEmojiPicker(emojiPickerPanel)
         updateSmileyButtonIcon()

app/src/main/java/com/nextcloud/talk/emojipicker/EmojiPickerPanel.kt

@@ -60,6 +60,14 @@ class EmojiPickerPanel @JvmOverloads constructor(
             updateSearchRowVisibility()
         }
 
+    /** Whether the host's target text actually has something for the backspace button to delete. */
+    var backspaceActionAvailable: Boolean = true
+        set(value) {
+            field = value
+            binding.emojiBackspaceButton.isEnabled = value
+            binding.emojiBackspaceButton.alpha = if (value) ENABLED_ALPHA else DISABLED_ALPHA
+        }
+
     var onEmojiPicked: ((String) -> Unit)? = null
     var onBackspaceClicked: (() -> Unit)? = null
 
@@ -70,6 +78,7 @@ class EmojiPickerPanel @JvmOverloads constructor(
         binding.emojiSearchFieldGroup.isVisible = searchEnabled
         updateBackspaceVisibility()
         updateSearchRowVisibility()
+        binding.emojiBackspaceButton.alpha = ENABLED_ALPHA
 
         binding.emojiPicker.setOnEmojiPickedListener { item -> onEmojiPicked?.invoke(item.emoji) }
         binding.emojiSearchInput.doAfterTextChanged { editable -> onSearchTextChanged(editable?.toString().orEmpty()) }
@@ -201,5 +210,7 @@ class EmojiPickerPanel @JvmOverloads constructor(
         private const val SEARCH_DEBOUNCE_MS = 150L
         private const val RESULT_TEXT_SIZE_SP = 28f
         private const val RESULT_PADDING_DP = 8
+        private const val ENABLED_ALPHA = 1f
+        private const val DISABLED_ALPHA = 0.38f
     }
 }