meshcore-open/lib/helpers/reaction_helper.dart

import '../widgets/emoji_picker.dart';

class ReactionInfo {
  final String targetHash;
  final String emoji;

  ReactionInfo({
    required this.targetHash,
    required this.emoji,
  });
}

class ReactionHelper {
  static List<String>? _cachedEmojis;

  /// Combined list of all reaction emojis in fixed order.
  /// Order must stay stable for index compatibility.
  static List<String> get reactionEmojis {
    return _cachedEmojis ??= [
      ...EmojiPicker.quickEmojis,
      ...EmojiPicker.smileys,
      ...EmojiPicker.gestures,
      ...EmojiPicker.hearts,
      ...EmojiPicker.objects,
    ];
  }

  /// Convert emoji to 2-char hex index. Returns null if emoji not in list.
  static String? emojiToIndex(String emoji) {
    final idx = reactionEmojis.indexOf(emoji);
    if (idx < 0) return null;
    return idx.toRadixString(16).padLeft(2, '0');
  }

  /// Convert 2-char hex index to emoji. Returns null if invalid index.
  static String? indexToEmoji(String hexIndex) {
    final idx = int.tryParse(hexIndex, radix: 16);
    if (idx == null || idx < 0 || idx >= reactionEmojis.length) return null;
    return reactionEmojis[idx];
  }

  /// Compute a 4-char hex hash for a message reaction.
  /// Hash input: timestampSeconds + [senderName] + first 5 chars of text
  /// For 1:1 chats, senderName can be null (sender is implicit).
  static String computeReactionHash(int timestampSeconds, String? senderName, String text) {
    final first5 = text.length >= 5 ? text.substring(0, 5) : text;
    final input = senderName != null
        ? '$timestampSeconds$senderName$first5'
        : '$timestampSeconds$first5';
    // Use hashCode and take lower 16 bits, format as 4 hex chars
    final hash = input.hashCode & 0xFFFF;
    return hash.toRadixString(16).padLeft(4, '0');
  }

  /// Parse reaction format: r:HASH:INDEX (where INDEX is 2-char hex emoji index)
  /// Returns null if text is not a valid reaction format
  static ReactionInfo? parseReaction(String text) {
    final regex = RegExp(r'^r:([0-9a-f]{4}):([0-9a-f]{2})$');
    final match = regex.firstMatch(text);
    if (match == null) return null;

    final emoji = indexToEmoji(match.group(2)!);
    if (emoji == null) return null;

    return ReactionInfo(
      targetHash: match.group(1)!,
      emoji: emoji,
    );
  }
}