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);
    }
  }
}