Complete refactor to clean up project

lib/features/sheet_viewer/widgets/paint_mode_layer.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_drawing_board/flutter_drawing_board.dart';
+
+import 'pdf_page_display.dart';
+
+/// Drawing overlay for annotating PDF pages.
+///
+/// Uses flutter_drawing_board to provide a paint canvas over the PDF.
+/// Only available in single-page mode.
+class PaintModeLayer extends StatelessWidget {
+  final PdfPageDisplay pageDisplay;
+
+  const PaintModeLayer({
+    super.key,
+    required this.pageDisplay,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox.expand(
+      child: LayoutBuilder(
+        builder: (context, constraints) {
+          final maxSize = Size(constraints.maxWidth, constraints.maxHeight);
+          final (pageSize, _) = pageDisplay.calculateScaledPageSizes(maxSize);
+
+          return DrawingBoard(
+            background: SizedBox(
+              width: pageSize.width,
+              height: pageSize.height,
+              child: pageDisplay,
+            ),
+            boardConstrained: true,
+            minScale: 1,
+            maxScale: 3,
+            alignment: Alignment.topRight,
+            boardBoundaryMargin: EdgeInsets.zero,
+          );
+        },
+      ),
+    );
+  }
+}

lib/features/sheet_viewer/widgets/pdf_page_display.dart

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+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import 'package:pdfrx/pdfrx.dart';
+
+import '../../../core/models/config.dart';
+
+/// Displays PDF pages with optional two-page mode.
+class PdfPageDisplay extends StatelessWidget {
+  final PdfDocument document;
+  final int numPages;
+  final int currentPageNumber;
+  final Config config;
+
+  const PdfPageDisplay({
+    super.key,
+    required this.document,
+    required this.numPages,
+    required this.currentPageNumber,
+    required this.config,
+  });
+
+  /// Whether two-page mode is active and we have enough pages.
+  bool get _showTwoPages => config.twoPageMode && numPages >= 2;
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      mainAxisAlignment: MainAxisAlignment.center,
+      crossAxisAlignment: CrossAxisAlignment.center,
+      children: [_buildLeftPage(), if (_showTwoPages) _buildRightPage()],
+    );
+  }
+
+  Widget _buildLeftPage() {
+    return Expanded(
+      child: Stack(
+        children: [
+          PdfPageView(
+            key: ValueKey(currentPageNumber),
+            document: document,
+            pageNumber: currentPageNumber,
+            maximumDpi: 300,
+            alignment: _showTwoPages ? Alignment.centerRight : Alignment.center,
+          ),
+          _buildPageIndicator(currentPageNumber),
+        ],
+      ),
+    );
+  }
+
+  Widget _buildRightPage() {
+    final rightPageNumber = currentPageNumber + 1;
+
+    return Expanded(
+      child: Stack(
+        children: [
+          PdfPageView(
+            key: ValueKey(rightPageNumber),
+            document: document,
+            pageNumber: rightPageNumber,
+            maximumDpi: 300,
+            alignment: Alignment.centerLeft,
+          ),
+          _buildPageIndicator(rightPageNumber),
+        ],
+      ),
+    );
+  }
+
+  Widget _buildPageIndicator(int pageNumber) {
+    return Positioned.fill(
+      child: Container(
+        alignment: Alignment.bottomCenter,
+        padding: const EdgeInsets.only(bottom: 5),
+        child: Text('$pageNumber / $numPages'),
+      ),
+    );
+  }
+
+  // ---------------------------------------------------------------------------
+  // Page Size Calculations
+  // ---------------------------------------------------------------------------
+
+  /// Calculates scaled page sizes for the current view.
+  ///
+  /// Returns a tuple of (leftPageSize, rightPageSize).
+  /// rightPageSize is null when not in two-page mode.
+  (Size, Size?) calculateScaledPageSizes(Size parentSize) {
+    if (config.twoPageMode) {
+      return _calculateTwoPageSizes(parentSize);
+    }
+    return (_calculateSinglePageSize(parentSize), null);
+  }
+
+  (Size, Size?) _calculateTwoPageSizes(Size parentSize) {
+    final leftSize = _getUnscaledPageSize(currentPageNumber);
+    final rightSize = numPages > currentPageNumber
+        ? _getUnscaledPageSize(currentPageNumber + 1)
+        : leftSize;
+
+    // Combine pages for scaling calculation
+    final combinedSize = Size(
+      leftSize.width + rightSize.width,
+      max(leftSize.height, rightSize.height),
+    );
+
+    final scaledCombined = _scaleToFit(parentSize, combinedSize);
+    final scaleFactor = scaledCombined.width / combinedSize.width;
+
+    return (leftSize * scaleFactor, rightSize * scaleFactor);
+  }
+
+  Size _calculateSinglePageSize(Size parentSize) {
+    return _scaleToFit(parentSize, _getUnscaledPageSize(currentPageNumber));
+  }
+
+  Size _getUnscaledPageSize(int pageNumber) {
+    return document.pages.elementAt(pageNumber - 1).size;
+  }
+
+  /// Scales a page size to fit within parent bounds while maintaining aspect ratio.
+  Size _scaleToFit(Size parentSize, Size pageSize) {
+    // Determine if height or width is the limiting factor
+    if (parentSize.aspectRatio > pageSize.aspectRatio) {
+      // Constrained by height
+      final height = parentSize.height;
+      final width = height * pageSize.aspectRatio;
+      return Size(width, height);
+    } else {
+      // Constrained by width
+      final width = parentSize.width;
+      final height = width / pageSize.aspectRatio;
+      return Size(width, height);
+    }
+  }
+}

lib/features/sheet_viewer/widgets/touch_navigation_layer.dart

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+import 'package:flutter/material.dart';
+
+import '../../../core/models/config.dart';
+import 'pdf_page_display.dart';
+
+/// Callback for page turn events.
+typedef PageTurnCallback = void Function(int delta);
+
+/// Gesture layer for touch-based navigation over PDF pages.
+///
+/// Touch zones:
+/// - Top 2cm: Toggle fullscreen (or exit if in fullscreen + top-right corner)
+/// - Left side: Turn page backward (-1 or -2 in two-page mode)
+/// - Right side: Turn page forward (+1 or +2 in two-page mode)
+class TouchNavigationLayer extends StatelessWidget {
+  final PdfPageDisplay pageDisplay;
+  final Config config;
+  final VoidCallback onToggleFullscreen;
+  final VoidCallback onExit;
+  final PageTurnCallback onPageTurn;
+
+  const TouchNavigationLayer({
+    super.key,
+    required this.pageDisplay,
+    required this.config,
+    required this.onToggleFullscreen,
+    required this.onExit,
+    required this.onPageTurn,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return GestureDetector(
+      behavior: HitTestBehavior.opaque,
+      onTapUp: (details) => _handleTap(context, details),
+      child: pageDisplay,
+    );
+  }
+
+  void _handleTap(BuildContext context, TapUpDetails details) {
+    final mediaQuery = MediaQuery.of(context);
+    final position = details.localPosition;
+
+    // Calculate physical measurements for consistent touch zones
+    final pixelsPerCm = _calculatePixelsPerCm(mediaQuery.devicePixelRatio);
+    final touchZoneHeight = 2 * pixelsPerCm;
+    final touchZoneWidth = 2 * pixelsPerCm;
+
+    final screenWidth = mediaQuery.size.width;
+    final screenCenter = screenWidth / 2;
+
+    // Get page sizes for accurate touch zone calculation
+    final (leftPageSize, rightPageSize) = pageDisplay.calculateScaledPageSizes(
+      mediaQuery.size,
+    );
+
+    // Check top zone first
+    if (position.dy < touchZoneHeight) {
+      _handleTopZoneTap(position, screenWidth, touchZoneWidth);
+      return;
+    }
+
+    // Handle page turning based on tap position
+    _handlePageTurnTap(position, screenCenter, leftPageSize, rightPageSize);
+  }
+
+  void _handleTopZoneTap(
+    Offset position,
+    double screenWidth,
+    double touchZoneWidth,
+  ) {
+    // Top-right corner in fullscreen mode = exit
+    if (config.fullscreen && position.dx >= screenWidth - touchZoneWidth) {
+      onExit();
+    } else {
+      onToggleFullscreen();
+    }
+  }
+
+  void _handlePageTurnTap(
+    Offset position,
+    double screenCenter,
+    Size leftPageSize,
+    Size? rightPageSize,
+  ) {
+    final isLeftSide = position.dx < screenCenter;
+
+    if (config.twoPageMode) {
+      _handleTwoPageModeTap(
+        position,
+        screenCenter,
+        leftPageSize,
+        rightPageSize,
+      );
+    } else {
+      // Single page mode: simple left/right
+      onPageTurn(isLeftSide ? -1 : 1);
+    }
+  }
+
+  void _handleTwoPageModeTap(
+    Offset position,
+    double screenCenter,
+    Size leftPageSize,
+    Size? rightPageSize,
+  ) {
+    final leftEdge = screenCenter - leftPageSize.width / 2;
+    final rightEdge = screenCenter + (rightPageSize?.width ?? 0) / 2;
+
+    if (position.dx < leftEdge) {
+      onPageTurn(-2);
+    } else if (position.dx < screenCenter) {
+      onPageTurn(-1);
+    } else if (position.dx > rightEdge) {
+      onPageTurn(2);
+    } else {
+      onPageTurn(1);
+    }
+  }
+
+  double _calculatePixelsPerCm(double devicePixelRatio) {
+    const baseDpi = 160.0; // Android baseline DPI
+    const cmPerInch = 2.54;
+    return (devicePixelRatio * baseDpi) / cmPerInch;
+  }
+}