feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

mobile/lib/features/channels/message_media.dart

@@ -0,0 +1,116 @@
+import 'package:flutter/foundation.dart';
+
+enum MessageMediaKind { image, video }
+
+@immutable
+class ImetaEntry {
+  final String url;
+  final String? mimeType;
+  final String? dimensions;
+  final String? thumb;
+  final String? image;
+  final String? alt;
+
+  const ImetaEntry({
+    required this.url,
+    this.mimeType,
+    this.dimensions,
+    this.thumb,
+    this.image,
+    this.alt,
+  });
+
+  bool get isVideo => mimeType?.startsWith('video/') == true;
+
+  String? get posterUrl => image ?? thumb;
+
+  double? get aspectRatio {
+    final parts = dimensions?.split('x');
+    if (parts == null || parts.length != 2) return null;
+    final width = double.tryParse(parts[0]);
+    final height = double.tryParse(parts[1]);
+    if (width == null || height == null || width <= 0 || height <= 0) {
+      return null;
+    }
+    return width / height;
+  }
+}
+
+Map<String, ImetaEntry> parseImetaTags(List<List<String>> tags) {
+  final byUrl = <String, ImetaEntry>{};
+  for (final tag in tags) {
+    if (tag.isEmpty || tag.first != 'imeta') continue;
+
+    String? url;
+    String? mimeType;
+    String? dimensions;
+    String? thumb;
+    String? image;
+    String? alt;
+
+    for (final part in tag.skip(1)) {
+      final separator = part.indexOf(' ');
+      if (separator <= 0) continue;
+      final key = part.substring(0, separator);
+      final value = part.substring(separator + 1);
+      switch (key) {
+        case 'url':
+          url = value;
+        case 'm':
+          mimeType = value;
+        case 'dim':
+          dimensions = value;
+        case 'thumb':
+          thumb = value;
+        case 'image':
+          image = value;
+        case 'alt':
+          alt = value;
+      }
+    }
+
+    if (url == null || url.isEmpty) continue;
+    byUrl[url] = ImetaEntry(
+      url: url,
+      mimeType: mimeType,
+      dimensions: dimensions,
+      thumb: thumb,
+      image: image,
+      alt: alt,
+    );
+  }
+  return byUrl;
+}
+
+MessageMediaKind? classifyMediaUrl(String url, {ImetaEntry? imeta}) {
+  final mimeType = imeta?.mimeType;
+  if (mimeType != null) {
+    // An imeta MIME type is authoritative. The native video player chooses
+    // whether the device can decode the specific codec/container; rejecting
+    // every non-MP4 video here prevents it from even trying.
+    if (mimeType.startsWith('video/')) return MessageMediaKind.video;
+    if (mimeType.startsWith('image/')) return MessageMediaKind.image;
+  }
+
+  final path = (Uri.tryParse(url)?.path ?? url).toLowerCase();
+  if (path.endsWith(_mp4Extension)) {
+    return MessageMediaKind.video;
+  }
+  if (_imageExtensions.any(path.endsWith)) {
+    return MessageMediaKind.image;
+  }
+  return null;
+}
+
+const _imageExtensions = {
+  '.jpg',
+  '.jpeg',
+  '.png',
+  '.webp',
+  '.bmp',
+  '.heic',
+  '.heif',
+  '.avif',
+};
+
+const _mp4Extension = '.mp4';