117 lines
4.0 KiB
Dart
117 lines
4.0 KiB
Dart
import 'package:characters/characters.dart';
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/// Detects chat messages that consist solely of emoji so the UI can render
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/// them enlarged (à la WhatsApp/iMessage).
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///
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/// Returns the font size to use for such a message, or `null` when [text]
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/// contains any non-emoji, non-whitespace character (i.e. render normally).
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const int _zwj = 0x200D;
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const int _vs15 = 0xFE0E;
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const int _vs16 = 0xFE0F;
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const int _keycap = 0x20E3;
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const int _skinToneStart = 0x1F3FB;
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const int _skinToneEnd = 0x1F3FF;
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/// Codepoints that only ever glue an emoji sequence together and never stand
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/// on their own — they don't disqualify a cluster from counting as emoji.
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bool _isModifier(int r) =>
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r == _zwj ||
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r == _vs15 ||
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r == _vs16 ||
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r == _keycap ||
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(r >= _skinToneStart && r <= _skinToneEnd) || // skin-tone modifiers
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(r >= 0xE0020 && r <= 0xE007F); // tag characters (flag sequences)
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/// The digits, `#` and `*` that become emoji only when combined with the
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/// keycap combining mark.
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bool _isKeycapBase(int r) =>
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r == 0x23 || r == 0x2A || (r >= 0x30 && r <= 0x39);
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bool _isEmojiRune(int r) {
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// Bulk of modern emoji live in the astral pictograph block: emoticons,
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// transport, supplemental symbols, extended-A, regional indicators, …
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if (r >= 0x1F000 && r <= 0x1FAFF) return true;
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// Scattered BMP emoji ranges (misc symbols, dingbats, arrows, stars, …).
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if (r >= 0x2600 && r <= 0x27BF) return true;
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if (r >= 0x2300 && r <= 0x23FF) return true;
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if (r >= 0x2B00 && r <= 0x2BFF) return true;
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if (r >= 0x2190 && r <= 0x21FF) return true;
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if (r >= 0x25A0 && r <= 0x25FF) return true;
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const singles = {
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0x00A9, 0x00AE, 0x203C, 0x2049, 0x2122, 0x2139,
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0x2934, 0x2935, 0x3030, 0x303D, 0x3297, 0x3299, 0x24C2,
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};
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return singles.contains(r);
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}
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bool _isEmojiCluster(String cluster) {
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final runes = cluster.runes.toList(growable: false);
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final hasKeycap = runes.contains(_keycap);
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var hasEmoji = false;
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for (final r in runes) {
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if (_isModifier(r)) continue;
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if (_isEmojiRune(r)) {
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hasEmoji = true;
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continue;
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}
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if (hasKeycap && _isKeycapBase(r)) {
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hasEmoji = true;
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continue;
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}
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return false; // a plain text character → not an emoji cluster
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}
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return hasEmoji;
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}
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/// Maximum number of emojis a message may contain to still be enlarged; longer
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/// emoji strings would turn into a wall of giant glyphs and render normally.
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const int _maxEnlargedEmojis = 3;
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/// Font size for an emoji-only [text] of at most [_maxEnlargedEmojis] emojis.
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/// `null` means the message is not emoji-only (or has too many emojis) and
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/// should render at the normal body size.
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double? standaloneEmojiFontSize(String text) {
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final trimmed = text.trim();
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if (trimmed.isEmpty) return null;
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var count = 0;
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for (final cluster in trimmed.characters) {
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if (cluster.trim().isEmpty) continue; // whitespace between emojis
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if (!_isEmojiCluster(cluster)) return null;
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count++;
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if (count > _maxEnlargedEmojis) return null;
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}
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if (count == 0) return null;
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return 34;
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}
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/// [emoji] with any Fitzpatrick skin-tone modifier stripped, so tone variants
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/// of the same emoji compare equal (👍🏻 → 👍). Used to dedupe reactions that
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/// only differ in skin tone.
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String emojiSkinToneNeutral(String emoji) => String.fromCharCodes(
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emoji.runes.where((r) => r < _skinToneStart || r > _skinToneEnd),
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);
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/// Distinct emojis contained in [text], most-frequent first with ties broken
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/// by first appearance. Used to offer a message's own emojis as quick
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/// reactions.
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List<String> extractEmojis(String text) {
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final counts = <String, int>{};
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final firstSeen = <String, int>{};
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var order = 0;
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for (final cluster in text.characters) {
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if (!_isEmojiCluster(cluster)) continue;
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counts.update(cluster, (value) => value + 1, ifAbsent: () => 1);
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firstSeen.putIfAbsent(cluster, () => order++);
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}
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final emojis = counts.keys.toList();
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emojis.sort((a, b) {
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final byCount = counts[b]!.compareTo(counts[a]!);
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return byCount != 0 ? byCount : firstSeen[a]!.compareTo(firstSeen[b]!);
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});
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return emojis;
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}
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