android: upgrade fullscreen media viewer header and gallery

android/CHANGELOG.md

@@ -275,3 +275,9 @@
 - Added file-list style attachment rows (icon + filename + type/size metadata).
 - Upgraded non-voice audio attachment player with play/pause, progress bar, and current/total duration labels.
 - Updated Telegram UI batch-2 checklist media-bubble items.
+
+### Step 46 - Media viewer / header and gallery navigation
+- Upgraded chat image viewer to use global image gallery state (`index / total`) instead of a single URL.
+- Added fullscreen viewer header with close, index, share placeholder, and delete placeholder actions.
+- Added image navigation controls (`Prev`/`Next`) for gallery traversal.
+- Updated Telegram UI batch-2 checklist for fullscreen media header support.

android/app/src/main/java/ru/daemonlord/messenger/ui/chat/ChatScreen.kt

@@ -123,7 +123,15 @@ fun ChatScreen(
     onLoadMore: () -> Unit,
     onPickMedia: () -> Unit,
 ) {
-    var viewerImageUrl by remember { mutableStateOf<String?>(null) }
+    val allImageUrls = remember(state.messages) {
+        state.messages
+            .flatMap { message -> message.attachments }
+            .map { it.fileUrl to it.fileType.lowercase() }
+            .filter { (_, type) -> type.startsWith("image/") }
+            .map { (url, _) -> url }
+            .distinct()
+    }
+    var viewerImageIndex by remember { mutableStateOf<Int?>(null) }
     var dismissedPinnedMessageId by remember { mutableStateOf<Long?>(null) }
     var actionMenuMessage by remember { mutableStateOf<MessageItem?>(null) }
     Column(
@@ -241,7 +249,10 @@ fun ChatScreen(
                             message = message,
                             isSelected = isSelected,
                             reactions = state.reactionByMessageId[message.id].orEmpty(),
-                            onAttachmentImageClick = { imageUrl -> viewerImageUrl = imageUrl },
+                            onAttachmentImageClick = { imageUrl ->
+                                val idx = allImageUrls.indexOf(imageUrl)
+                                viewerImageIndex = if (idx >= 0) idx else null
+                            },
                             onClick = {
                                 actionMenuMessage = null
                                 if (state.actionState.mode == MessageSelectionMode.MULTI) {
@@ -495,22 +506,71 @@ fun ChatScreen(
             )
         }
 
-        if (viewerImageUrl != null) {
+        if (viewerImageIndex != null) {
+            val currentIndex = viewerImageIndex ?: 0
+            val currentUrl = allImageUrls.getOrNull(currentIndex)
             Surface(
                 modifier = Modifier
                     .fillMaxSize()
                     .background(MaterialTheme.colorScheme.scrim.copy(alpha = 0.7f))
-                    .clickable { viewerImageUrl = null },
+                    .clickable { },
             ) {
-                Box(contentAlignment = Alignment.Center) {
-                    AsyncImage(
-                        model = viewerImageUrl,
-                        contentDescription = "Attachment",
+                Column(modifier = Modifier.fillMaxSize()) {
+                    Row(
                         modifier = Modifier
                             .fillMaxWidth()
-                            .padding(16.dp),
-                        contentScale = ContentScale.Fit,
-                    )
+                            .padding(horizontal = 12.dp, vertical = 10.dp),
+                        horizontalArrangement = Arrangement.SpaceBetween,
+                        verticalAlignment = Alignment.CenterVertically,
+                    ) {
+                        Button(onClick = { viewerImageIndex = null }) { Text("✕") }
+                        Text(
+                            text = "${currentIndex + 1}/${allImageUrls.size.coerceAtLeast(1)}",
+                            style = MaterialTheme.typography.titleSmall,
+                        )
+                        Row(horizontalArrangement = Arrangement.spacedBy(6.dp)) {
+                            Button(onClick = {}, enabled = false) { Text("↗") }
+                            Button(onClick = {}, enabled = false) { Text("🗑") }
+                        }
+                    }
+                    Box(
+                        modifier = Modifier.weight(1f),
+                        contentAlignment = Alignment.Center,
+                    ) {
+                        if (currentUrl != null) {
+                            AsyncImage(
+                                model = currentUrl,
+                                contentDescription = "Attachment",
+                                modifier = Modifier
+                                    .fillMaxWidth()
+                                    .padding(16.dp),
+                                contentScale = ContentScale.Fit,
+                            )
+                        }
+                    }
+                    Row(
+                        modifier = Modifier
+                            .fillMaxWidth()
+                            .padding(horizontal = 16.dp, vertical = 10.dp),
+                        horizontalArrangement = Arrangement.SpaceBetween,
+                    ) {
+                        Button(
+                            onClick = {
+                                viewerImageIndex = if (allImageUrls.isEmpty()) null else {
+                                    (currentIndex - 1).coerceAtLeast(0)
+                                }
+                            },
+                            enabled = currentIndex > 0,
+                        ) { Text("Prev") }
+                        Button(
+                            onClick = {
+                                viewerImageIndex = if (allImageUrls.isEmpty()) null else {
+                                    (currentIndex + 1).coerceAtMost(allImageUrls.lastIndex)
+                                }
+                            },
+                            enabled = currentIndex < allImageUrls.lastIndex,
+                        ) { Text("Next") }
+                    }
                 }
             }
         }

docs/android-ui-batch-2-checklist.md

@@ -35,7 +35,7 @@
 - [ ] Метаданные поста/канала (просмотры/время/reaction strip) у медиа-сообщений.
 
 ## P1 — Fullscreen Media Viewer
-- [ ] Fullscreen header: close + index ("1") + share + delete.
+- [x] Fullscreen header: close + index ("1") + share + delete.
 - [ ] Поддержка reaction overlay в viewer (как на скрине).
 - [ ] Свайп между медиа (gallery mode), если в сообщении несколько вложений.