buzz/mobile/lib/features/channels/message_content/channel_token_pattern.dart

/// Matches inline `#channel` tokens. The message body and its one-line
/// preview share it so they always agree on what is a channel token.
library;

/// Only [knownNames] match, longest first so `#eng-ios` wins over `#eng`.
/// That keeps `#8700` or `#123` in prose as text instead of an inert chip.
/// With no known names (channels still loading, or none visible) nothing
/// matches; the message rebuilds with chips once channel names arrive.
///
/// A token can't start inside a word, path or URL (`a#b`, `x.y/#z`), and it
/// ends at whitespace, the end of a line, or punctuation that commonly follows
/// a word in prose: `#general's`, `"#general"`, `#general…`, `#general—`.
RegExp channelTokenPattern(Iterable<String> knownNames) {
  final names =
      knownNames
          .map((name) => name.trim())
          .where((name) => name.isNotEmpty)
          .toSet()
          .toList()
        ..sort((a, b) => b.length.compareTo(a.length));
  if (names.isEmpty) return _noMatch;
  return RegExp(
    '$_leading#(?:${names.map(RegExp.escape).join('|')})$_trailing',
    caseSensitive: false,
    multiLine: true,
  );
}

final _noMatch = RegExp(r'(?!)');
const _leading = r'(?<![\w./:-])';
const _trailing =
    r'(?=$|[\s,;.!?:)\]}'
    "'\"\u2018\u2019\u201C\u201D\u00BB\u2026\u2013\u2014"
    r'])';