Custom drawing implementation

lib/features/sheet_viewer/drawing/drawing_controller.dart

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+import 'dart:convert';
+
+import 'package:flutter/material.dart';
+
+import 'drawing_line.dart';
+import 'paint_preset.dart';
+
+/// Controller for managing drawing state with undo/redo support.
+///
+/// Manages a stack of [DrawingLine] objects and provides methods for
+/// drawing, undoing, redoing, and serializing the drawing state.
+class DrawingController extends ChangeNotifier {
+  /// All completed lines in the drawing
+  final List<DrawingLine> _lines = [];
+
+  /// Lines that have been undone (for redo functionality)
+  final List<DrawingLine> _undoneLines = [];
+
+  /// The line currently being drawn (null when not drawing)
+  DrawingLine? _currentLine;
+
+  /// Current paint preset being used
+  PaintPreset _currentPreset = PaintPreset.blackPen;
+
+  /// Maximum number of history steps to keep
+  final int maxHistorySteps;
+
+  DrawingController({this.maxHistorySteps = 50});
+
+  // ---------------------------------------------------------------------------
+  // Getters
+  // ---------------------------------------------------------------------------
+
+  /// All completed lines (read-only)
+  List<DrawingLine> get lines => List.unmodifiable(_lines);
+
+  /// The line currently being drawn
+  DrawingLine? get currentLine => _currentLine;
+
+  /// Current paint preset
+  PaintPreset get currentPreset => _currentPreset;
+
+  /// Whether undo is available
+  bool get canUndo => _lines.isNotEmpty;
+
+  /// Whether redo is available
+  bool get canRedo => _undoneLines.isNotEmpty;
+
+  // ---------------------------------------------------------------------------
+  // Drawing Operations
+  // ---------------------------------------------------------------------------
+
+  /// Starts a new line at the given normalized position.
+  void startLine(Offset normalizedPoint) {
+    _currentLine = DrawingLine(
+      points: [normalizedPoint],
+      color: _currentPreset.color,
+      strokeWidth: _currentPreset.strokeWidth,
+    );
+    notifyListeners();
+  }
+
+  /// Adds a point to the current line.
+  void addPoint(Offset normalizedPoint) {
+    if (_currentLine == null) return;
+
+    _currentLine = _currentLine!.addPoint(normalizedPoint);
+    notifyListeners();
+  }
+
+  /// Completes the current line and adds it to the history.
+  void endLine() {
+    if (_currentLine == null) return;
+
+    // Only add lines with at least 2 points
+    if (_currentLine!.points.length >= 2) {
+      _lines.add(_currentLine!);
+      // Clear redo stack when new action is performed
+      _undoneLines.clear();
+      _trimHistory();
+    }
+
+    _currentLine = null;
+    notifyListeners();
+  }
+
+  /// Trims history to maxHistorySteps to prevent memory growth.
+  void _trimHistory() {
+    while (_lines.length > maxHistorySteps) {
+      _lines.removeAt(0);
+    }
+  }
+
+  // ---------------------------------------------------------------------------
+  // Undo/Redo
+  // ---------------------------------------------------------------------------
+
+  /// Undoes the last line drawn.
+  void undo() {
+    if (!canUndo) return;
+
+    final line = _lines.removeLast();
+    _undoneLines.add(line);
+    notifyListeners();
+  }
+
+  /// Redoes the last undone line.
+  void redo() {
+    if (!canRedo) return;
+
+    final line = _undoneLines.removeLast();
+    _lines.add(line);
+    notifyListeners();
+  }
+
+  /// Clears all lines from the canvas.
+  void clear() {
+    _lines.clear();
+    _undoneLines.clear();
+    _currentLine = null;
+    notifyListeners();
+  }
+
+  // ---------------------------------------------------------------------------
+  // Paint Preset
+  // ---------------------------------------------------------------------------
+
+  /// Sets the current paint preset.
+  void setPreset(PaintPreset preset) {
+    _currentPreset = preset;
+    notifyListeners();
+  }
+
+  // ---------------------------------------------------------------------------
+  // Serialization
+  // ---------------------------------------------------------------------------
+
+  /// Exports all lines to a JSON-serializable list.
+  List<Map<String, dynamic>> toJsonList() {
+    return _lines.map((line) => line.toJson()).toList();
+  }
+
+  /// Exports all lines to a JSON string.
+  String toJsonString() {
+    return jsonEncode(toJsonList());
+  }
+
+  /// Imports lines from a JSON-serializable list.
+  void fromJsonList(List<Map<String, dynamic>> jsonList) {
+    _lines.clear();
+    _undoneLines.clear();
+    _currentLine = null;
+
+    for (final json in jsonList) {
+      _lines.add(DrawingLine.fromJson(json));
+    }
+
+    notifyListeners();
+  }
+
+  /// Imports lines from a JSON string.
+  void fromJsonString(String jsonString) {
+    if (jsonString.isEmpty || jsonString == '[]') {
+      clear();
+      return;
+    }
+
+    final decoded = jsonDecode(jsonString) as List;
+    if (decoded.isEmpty) {
+      clear();
+      return;
+    }
+    fromJsonList(decoded.cast<Map<String, dynamic>>());
+  }
+
+  /// Adds existing lines without clearing (for merging annotations).
+  void addLines(List<DrawingLine> newLines) {
+    _lines.addAll(newLines);
+    _trimHistory();
+    notifyListeners();
+  }
+
+  @override
+  void dispose() {
+    _lines.clear();
+    _undoneLines.clear();
+    super.dispose();
+  }
+}