trainhub-flutter/lib/data/services/combo_service.dart

import 'dart:convert';
import 'dart:io';
import 'dart:math';

import 'package:flutter/foundation.dart';
import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';
import 'package:uuid/uuid.dart';

const _uuid = Uuid();

/// One technique node in a combo graph.
class ComboNode {
  const ComboNode({
    required this.id,
    required this.technique,
    this.translation = '',
    required this.dx,
    required this.dy,
  });

  final String id;
  final String technique;
  final String translation;
  final double dx;
  final double dy;

  ComboNode copyWith({double? dx, double? dy}) => ComboNode(
    id: id,
    technique: technique,
    translation: translation,
    dx: dx ?? this.dx,
    dy: dy ?? this.dy,
  );

  Map<String, dynamic> toJson() => {
    'id': id,
    'technique': technique,
    'translation': translation,
    'dx': dx,
    'dy': dy,
  };

  factory ComboNode.fromJson(Map<String, dynamic> json) => ComboNode(
    id: json['id'] as String,
    technique: json['technique'] as String,
    translation: (json['translation'] ?? '') as String,
    dx: (json['dx'] as num).toDouble(),
    dy: (json['dy'] as num).toDouble(),
  );
}

/// A directed transition between two techniques.
class ComboEdge {
  const ComboEdge(this.fromId, this.toId);

  final String fromId;
  final String toId;

  Map<String, dynamic> toJson() => {'from': fromId, 'to': toId};

  factory ComboEdge.fromJson(Map<String, dynamic> json) =>
      ComboEdge(json['from'] as String, json['to'] as String);
}

/// A named technique graph: nodes are techniques, edges are the transitions
/// that make sense between them.
class Combo {
  const Combo({
    required this.id,
    required this.name,
    this.nodes = const [],
    this.edges = const [],
  });

  final String id;
  final String name;
  final List<ComboNode> nodes;
  final List<ComboEdge> edges;

  Combo copyWith({
    String? name,
    List<ComboNode>? nodes,
    List<ComboEdge>? edges,
  }) => Combo(
    id: id,
    name: name ?? this.name,
    nodes: nodes ?? this.nodes,
    edges: edges ?? this.edges,
  );

  Map<String, dynamic> toJson() => {
    'id': id,
    'name': name,
    'nodes': nodes.map((n) => n.toJson()).toList(),
    'edges': edges.map((e) => e.toJson()).toList(),
  };

  factory Combo.fromJson(Map<String, dynamic> json) => Combo(
    id: json['id'] as String,
    name: json['name'] as String,
    nodes: [
      for (final n in (json['nodes'] as List? ?? []))
        ComboNode.fromJson(n as Map<String, dynamic>),
    ],
    edges: [
      for (final e in (json['edges'] as List? ?? []))
        ComboEdge.fromJson(e as Map<String, dynamic>),
    ],
  );

  /// Random walk over the graph — the generated combination to drill.
  /// Follows outgoing edges; if a node is a dead end the walk stops there.
  List<ComboNode> generateSequence({int length = 4, Random? random}) {
    if (nodes.isEmpty) return [];
    final rnd = random ?? Random();
    final byId = {for (final n in nodes) n.id: n};
    final outgoing = <String, List<String>>{};
    for (final e in edges) {
      outgoing.putIfAbsent(e.fromId, () => []).add(e.toId);
    }

    // Prefer starting somewhere that actually leads on.
    final starts = nodes.where((n) => outgoing.containsKey(n.id)).toList();
    var current = (starts.isEmpty
        ? nodes
        : starts)[rnd.nextInt((starts.isEmpty ? nodes : starts).length)];

    final sequence = <ComboNode>[current];
    while (sequence.length < length) {
      final next = outgoing[current.id];
      if (next == null || next.isEmpty) break;
      current = byId[next[rnd.nextInt(next.length)]]!;
      sequence.add(current);
    }
    return sequence;
  }
}

/// Loads and persists combos as a JSON file in the app documents dir.
class ComboService extends ChangeNotifier {
  static const _fileName = 'trainhub_combos.json';

  List<Combo> _combos = [];
  bool _loaded = false;

  List<Combo> get combos => _combos;

  Future<File> _file() async {
    final dir = await getApplicationDocumentsDirectory();
    return File(p.join(dir.path, _fileName));
  }

  Future<void> ensureLoaded() async {
    if (_loaded) return;
    _loaded = true;
    try {
      final file = await _file();
      if (!file.existsSync()) return;
      final json = jsonDecode(await file.readAsString()) as List<dynamic>;
      _combos = [
        for (final c in json) Combo.fromJson(c as Map<String, dynamic>),
      ];
      notifyListeners();
    } catch (e) {
      if (kDebugMode) debugPrint('Failed to load combos: $e');
    }
  }

  Combo create(String name) {
    final combo = Combo(id: _uuid.v4(), name: name);
    _combos = [..._combos, combo];
    notifyListeners();
    _persist();
    return combo;
  }

  void delete(String id) {
    _combos = _combos.where((c) => c.id != id).toList();
    notifyListeners();
    _persist();
  }

  /// Replaces a combo. Set [persist] false for high-frequency updates
  /// (node dragging) and call [persistNow] once afterwards.
  void update(Combo combo, {bool persist = true}) {
    _combos = [for (final c in _combos) c.id == combo.id ? combo : c];
    notifyListeners();
    if (persist) _persist();
  }

  void persistNow() => _persist();

  Future<void> _persist() async {
    try {
      final file = await _file();
      await file.writeAsString(
        jsonEncode(_combos.map((c) => c.toJson()).toList()),
      );
    } catch (e) {
      if (kDebugMode) debugPrint('Failed to save combos: $e');
    }
  }
}