import 'package:flutter/foundation.dart';

/// The standard (Unicode) emoji set, projected from the same emoji-mart dataset
/// desktop uses.
///
/// The asset at `assets/emoji/emoji-data.json` is generated by
/// `just mobile-emoji-data`; ids here are emoji-mart ids, which are exactly the
/// `:shortcode:` values desktop emits from its picker and resolves in
/// `emojiDisplayName`. Keeping both clients on one dataset is what stops a
/// shortcode from meaning different things on mobile and desktop.
@immutable
class EmojiEntry {
  /// emoji-mart id, i.e. the shortcode without the surrounding colons.
  final String id;

  /// Human-readable name, e.g. `Index Pointing Up`.
  final String name;

  /// Search keywords from the dataset.
  final List<String> keywords;

  /// The default-skin glyph.
  final String native;

  /// Position within emoji-mart's skin list. The default skin is zero.
  final int skinIndex;

  /// Owning category id, e.g. `people`.
  final String categoryId;

  const EmojiEntry({
    required this.id,
    required this.name,
    required this.keywords,
    required this.native,
    required this.categoryId,
    this.skinIndex = 0,
  });

  /// Unique tile id while preserving the desktop-identical shortcode for the
  /// default skin.
  String get tileId => skinIndex == 0 ? id : '$id-$skinIndex';
}

/// One dataset category, in emoji-mart's own order.
@immutable
class EmojiCategory {
  final String id;
  final List<EmojiEntry> emoji;

  const EmojiCategory({required this.id, required this.emoji});

  /// Title-cased label for the category rail.
  String get label => switch (id) {
    'people' => 'Smileys & People',
    'nature' => 'Animals & Nature',
    'foods' => 'Food & Drink',
    'activity' => 'Activity',
    'places' => 'Travel & Places',
    'objects' => 'Objects',
    'symbols' => 'Symbols',
    'flags' => 'Flags',
    _ => id,
  };
}

/// Parsed emoji dataset: ordered categories, a flat list for search, and a
/// reverse glyph index for resolving a reaction back to its shortcode.
@immutable
class EmojiDataset {
  final List<EmojiCategory> categories;

  /// Every entry, in category order. Search scans this.
  final List<EmojiEntry> all;

  /// Glyph to `:shortcode:`. Mirrors desktop's `emojiDisplayName`.
  final Map<String, String> nativeToShortcode;

  const EmojiDataset({
    required this.categories,
    required this.all,
    required this.nativeToShortcode,
  });

  static const empty = EmojiDataset(
    categories: [],
    all: [],
    nativeToShortcode: {},
  );

  bool get isEmpty => all.isEmpty;

  /// Resolve a reaction value to something displayable as a name: a custom
  /// emoji's `:shortcode:` passes through, a Unicode glyph maps to its
  /// shortcode, and anything unknown falls back to itself.
  String displayName(String emoji) {
    final trimmed = emoji.trim();
    if (trimmed.startsWith(':') && trimmed.endsWith(':')) return trimmed;
    return nativeToShortcode[trimmed] ?? trimmed;
  }

  /// Parse the generated asset. Runs on a background isolate via `compute`, so
  /// it must stay a top-level-callable pure function over plain JSON.
  static EmojiDataset fromJson(Map<String, dynamic> json) {
    final rawEmoji = (json['emoji'] as Map).cast<String, dynamic>();
    final rawCategories = (json['categories'] as List).cast<dynamic>();

    final categories = <EmojiCategory>[];
    final all = <EmojiEntry>[];
    final nativeToShortcode = <String, String>{};

    for (final rawCategory in rawCategories) {
      final category = (rawCategory as Map).cast<String, dynamic>();
      final categoryId = category['id'] as String;
      final entries = <EmojiEntry>[];

      for (final rawId in (category['emoji'] as List).cast<dynamic>()) {
        final id = rawId as String;
        final record = (rawEmoji[id] as Map?)?.cast<String, dynamic>();
        if (record == null) continue;
        // Older committed assets used one string; accept that shape so the
        // parser remains safe while generated assets move to all skin variants.
        final natives = switch (record['u']) {
          final List values => values.cast<String>(),
          final String value => [value],
          _ => const <String>[],
        };
        for (final (skinIndex, native) in natives.indexed) {
          final entry = EmojiEntry(
            id: id,
            name: record['n'] as String,
            keywords: (record['k'] as List).cast<String>(),
            native: native,
            categoryId: categoryId,
            skinIndex: skinIndex,
          );
          entries.add(entry);
          all.add(entry);
          // First writer wins so the earliest category owns a shared glyph,
          // matching desktop's map build order.
          nativeToShortcode.putIfAbsent(entry.native, () => ':$id:');
        }
      }

      categories.add(EmojiCategory(id: categoryId, emoji: entries));
    }

    return EmojiDataset(
      categories: categories,
      all: all,
      nativeToShortcode: nativeToShortcode,
    );
  }
}