import 'dart:typed_data';

import 'package:intl/intl.dart';
import 'package:pdf/pdf.dart';
import 'package:pdf/widgets.dart' as pw;

import 'fuel_report.dart';

final _dateFormat = DateFormat.yMMMd();
final _dateTimeFormat = DateFormat.yMMMd().add_jm();
final _monthFormat = DateFormat('MMM');
final _monthHeadingFormat = DateFormat.yMMMM();
final _dayMonthFormat = DateFormat('d MMM');
final _generatedFormat = DateFormat('d MMM yyyy');
final _currencyFormat = NumberFormat.simpleCurrency();

// Palette lifted from the report design mockup — kept in one place so
// every section (banner, cards, tables, watermark) draws from the same
// set of colors rather than each picking its own.
final _bannerBackground = PdfColor.fromHex('#EAF3DE');
final _bannerText = PdfColor.fromHex('#27500A');
final _textPrimary = PdfColor.fromHex('#1F1E1C');
final _textMuted = PdfColor.fromHex('#6B6A64');
final _textFaint = PdfColor.fromHex('#94938C');
final _borderLight = PdfColor.fromHex('#E5E3DB');
final _borderStrong = PdfColor.fromHex('#CFCDC4');
final _accentGreen = PdfColor.fromHex('#639922');
final _accentGreenDark = PdfColor.fromHex('#3B6D11');
final _cardBackground = PdfColor.fromHex('#F7F6F1');

final _tableBorder = pw.TableBorder.all(color: _borderLight, width: 0.5);
final _tableHeaderDecoration = pw.BoxDecoration(color: PdfColor.fromHex('#EFEEE7'));
final _tableEvenRowDecoration = const pw.BoxDecoration(color: PdfColors.white);
final _tableOddRowDecoration = pw.BoxDecoration(color: _cardBackground);
final _sectionHeadingStyle = pw.TextStyle(fontSize: 15, fontWeight: pw.FontWeight.bold, color: _textPrimary);

/// Renders [report] as a PDF, styled after the app's report design mockup:
/// a branded letterhead banner, a headline total, three at-a-glance stat
/// cards, a "gallons by month" bar chart + table, and a by-vehicle
/// breakdown. When requested, a "Line Items" section (a table per vehicle)
/// and/or a "Receipt Images" section (photos per vehicle, sized to
/// actually be legible — not a small inline thumbnail) follow, each
/// grouped by vehicle and sorted oldest-first within it. When both are on,
/// each line item and its receipt photo are tagged with the same number
/// (assigned once, continuing across vehicles) so the two can be matched
/// up by eye despite living in separate sections.
///
/// [receiptImages] supplies the actual photo bytes, keyed by
/// [FuelEntry.id] — see `loadReceiptImageBytes`; an entry with no entry in
/// that map (couldn't be read locally or downloaded) is left out of the
/// images section rather than shown as a broken image.
Future<Uint8List> buildFuelReportPdf(
  FuelReport report, {
  bool includeLineItems = false,
  bool includeReceiptImages = false,
  Map<String, Uint8List> receiptImages = const {},
}) async {
  final doc = pw.Document();
  final generatedAt = DateTime.now();

  doc.addPage(
    pw.MultiPage(
      pageFormat: PdfPageFormat.letter,
      margin: pw.EdgeInsets.zero,
      header: (context) => _buildBanner(generatedAt),
      footer: (context) => _buildFooter(report, context),
      build: (context) => _buildBody(
        report,
        includeLineItems: includeLineItems,
        includeReceiptImages: includeReceiptImages,
        receiptImages: receiptImages,
      ),
    ),
  );

  return doc.save();
}

/// A *flat* list of top-level widgets — deliberately not one big [pw.Column]
/// wrapping everything. [pw.MultiPage] paginates by walking its `build:`
/// list one top-level item at a time, resetting its "stuck" bookkeeping
/// only once each one fully finishes; a [pw.Table]/[pw.Wrap] (both of which
/// span pages on their own, e.g. a long line-items table or a big receipt
/// photo grid) nested *inside* one enclosing spanning [pw.Column] instead
/// of being its own top-level entry defeats that bookkeeping and throws
/// `TooManyPagesException` on anything long enough to need several page
/// breaks — even though the content itself is perfectly valid.
List<pw.Widget> _buildBody(
  FuelReport report, {
  required bool includeLineItems,
  required bool includeReceiptImages,
  required Map<String, Uint8List> receiptImages,
}) {
  pw.Widget pad(pw.Widget child) =>
      pw.Padding(padding: const pw.EdgeInsets.symmetric(horizontal: 36), child: child);

  if (report.rows.isEmpty) {
    return [
      pw.Padding(
        padding: const pw.EdgeInsets.fromLTRB(36, 20, 36, 0),
        child: _buildTitleBlock(report),
      ),
      pad(pw.Text('No vehicles had a receipted fuel entry in this date range.')),
    ];
  }

  final widgets = <pw.Widget>[
    pw.Padding(
      padding: const pw.EdgeInsets.fromLTRB(36, 20, 36, 0),
      child: _buildTitleBlock(report),
    ),
    pad(_buildHeroStat(report)),
    pw.SizedBox(height: 22),
    pad(_buildStatCardsRow(report)),
    pw.SizedBox(height: 26),
    pad(_buildMonthlySection(report)),
    pw.SizedBox(height: 26),
    pad(_buildVehicleSection(report)),
  ];

  if (includeLineItems || includeReceiptImages) {
    widgets.add(pw.SizedBox(height: 26));
    widgets.addAll(
      _buildLineItemsAndImagesSections(
        report,
        includeLineItems: includeLineItems,
        includeReceiptImages: includeReceiptImages,
        receiptImages: receiptImages,
      ).map(pad),
    );
  }

  widgets.add(pw.SizedBox(height: 8));
  return widgets;
}

pw.Widget _buildBanner(DateTime generatedAt) {
  // The watermark lives here, inside the banner's own bounded height,
  // rather than overlaid on the flowing body content below — a Stack
  // wrapping unbounded/multi-page content doesn't paginate (MultiPage
  // needs a SpanningWidget or a fixed-size child for that), so scoping it
  // to this fixed-height strip is what keeps it safe across page breaks.
  return pw.Container(
    color: _bannerBackground,
    child: pw.Stack(
      children: [
        pw.Positioned(
          right: 12,
          top: -14,
          child: pw.SizedBox(width: 60, height: 60, child: _buildWatermark(alpha: 0.14)),
        ),
        pw.Padding(
          padding: const pw.EdgeInsets.symmetric(horizontal: 36, vertical: 14),
          child: pw.Row(
            mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
            children: [
              pw.Text(
                'Show Me The Fuel Refund',
                style: pw.TextStyle(fontSize: 13, fontWeight: pw.FontWeight.bold, color: _bannerText),
              ),
              pw.Container(
                padding: const pw.EdgeInsets.symmetric(horizontal: 10, vertical: 4),
                decoration: pw.BoxDecoration(
                  color: PdfColors.white,
                  borderRadius: const pw.BorderRadius.all(pw.Radius.circular(8)),
                ),
                child: pw.Text(
                  'Generated ${_generatedFormat.format(generatedAt)}',
                  style: pw.TextStyle(fontSize: 10, color: _bannerText),
                ),
              ),
            ],
          ),
        ),
      ],
    ),
  );
}

pw.Widget _buildFooter(FuelReport report, pw.Context context) {
  return pw.Container(
    padding: const pw.EdgeInsets.fromLTRB(36, 8, 36, 20),
    decoration: pw.BoxDecoration(border: pw.Border(top: pw.BorderSide(color: _borderStrong, width: 0.5))),
    margin: const pw.EdgeInsets.only(top: 6),
    child: pw.Row(
      mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
      children: [
        pw.Text(
          '${report.fillCount} purchase${report.fillCount == 1 ? '' : 's'} · '
          '${report.rows.length} vehicle${report.rows.length == 1 ? '' : 's'} · '
          '${_dateFormat.format(report.startDate)} - ${_dateFormat.format(report.endDate)}',
          style: pw.TextStyle(fontSize: 9, color: _textFaint),
        ),
        pw.Text(
          'Page ${context.pageNumber} of ${context.pagesCount}',
          style: pw.TextStyle(fontSize: 9, color: _textFaint),
        ),
      ],
    ),
  );
}

/// A faint brand-colored fuel-can silhouette — purely decorative,
/// matching the report mockup's watermark shape.
pw.Widget _buildWatermark({required double alpha}) {
  const svg = '''
<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <path d="M12,8 L76,8 L79,22 L73,33 L83,47 L78,58 L84,67 L86,89 L77,89 L77,70 L20,70 L20,30 Z" fill="#639922"/>
</svg>
''';
  return pw.SvgImage(svg: svg, colorFilter: _accentGreen.withAlpha(alpha));
}

pw.Widget _buildTitleBlock(FuelReport report) {
  final months = report.monthlyTotals.length;
  final vehicles = report.rows.length;
  final fills = report.fillCount;
  final subtitle = StringBuffer('${_dateFormat.format(report.startDate)} - ${_dateFormat.format(report.endDate)}');
  if (report.rows.isNotEmpty) {
    subtitle.write(
      ' · $months month${months == 1 ? '' : 's'} · $vehicles vehicle${vehicles == 1 ? '' : 's'} · '
      '$fills fill-up${fills == 1 ? '' : 's'}',
    );
  }

  return pw.Padding(
    padding: const pw.EdgeInsets.only(bottom: 20),
    child: pw.Column(
      crossAxisAlignment: pw.CrossAxisAlignment.start,
      children: [
        pw.Text('Fuel Report', style: pw.TextStyle(fontSize: 22, fontWeight: pw.FontWeight.bold, color: _textPrimary)),
        pw.SizedBox(height: 3),
        pw.Text(subtitle.toString(), style: pw.TextStyle(fontSize: 12, color: _textMuted)),
      ],
    ),
  );
}

pw.Widget _buildHeroStat(FuelReport report) {
  return pw.Column(
    crossAxisAlignment: pw.CrossAxisAlignment.start,
    children: [
      pw.Text('Total fuel purchased', style: pw.TextStyle(fontSize: 11, color: _textMuted)),
      pw.SizedBox(height: 4),
      pw.Row(
        crossAxisAlignment: pw.CrossAxisAlignment.end,
        children: [
          pw.Text(
            report.totalGallons.toStringAsFixed(3),
            style: pw.TextStyle(fontSize: 34, fontWeight: pw.FontWeight.bold, color: _accentGreenDark),
          ),
          pw.SizedBox(width: 6),
          pw.Padding(
            padding: const pw.EdgeInsets.only(bottom: 5),
            child: pw.Text('gal', style: pw.TextStyle(fontSize: 13, color: _accentGreenDark)),
          ),
        ],
      ),
    ],
  );
}

pw.Widget _buildStatCardsRow(FuelReport report) {
  pw.Widget statCard(String label, String value) => pw.Expanded(
        child: pw.Container(
          padding: const pw.EdgeInsets.all(10),
          decoration: pw.BoxDecoration(
            color: _cardBackground,
            borderRadius: const pw.BorderRadius.all(pw.Radius.circular(6)),
          ),
          child: pw.Column(
            crossAxisAlignment: pw.CrossAxisAlignment.start,
            children: [
              pw.Text(label, style: pw.TextStyle(fontSize: 10, color: _textMuted)),
              pw.SizedBox(height: 3),
              pw.Text(value, style: pw.TextStyle(fontSize: 15, fontWeight: pw.FontWeight.bold, color: _textPrimary)),
            ],
          ),
        ),
      );

  return pw.Row(
    children: [
      statCard('Spent at the pump', _currencyFormat.format(report.totalCost)),
      pw.SizedBox(width: 10),
      statCard('Avg price/gal', _currencyFormat.format(report.avgPricePerGallon)),
      pw.SizedBox(width: 10),
      statCard('Fill-ups logged', report.fillCount.toString()),
    ],
  );
}

pw.Widget _buildMonthlySection(FuelReport report) {
  final months = report.monthlyTotals;
  if (months.isEmpty) return pw.SizedBox();

  const chartHeight = 64.0;
  final maxGallons = months.fold(0.0, (max, m) => m.totalGallons > max ? m.totalGallons : max);

  return pw.Column(
    crossAxisAlignment: pw.CrossAxisAlignment.start,
    children: [
      pw.Text('Gallons by month', style: pw.TextStyle(fontSize: 11, color: _textMuted)),
      pw.SizedBox(height: 8),
      if (months.length > 1) ...[
        pw.SizedBox(
          height: chartHeight,
          child: pw.Row(
            crossAxisAlignment: pw.CrossAxisAlignment.end,
            children: [
              for (final month in months)
                pw.Expanded(
                  child: pw.Padding(
                    padding: const pw.EdgeInsets.symmetric(horizontal: 3),
                    child: pw.Container(
                      height: maxGallons == 0
                          ? 2
                          : (chartHeight * (month.totalGallons / maxGallons)).clamp(2, chartHeight),
                      decoration: pw.BoxDecoration(
                        color: _accentGreen,
                        borderRadius: const pw.BorderRadius.only(
                          topLeft: pw.Radius.circular(2),
                          topRight: pw.Radius.circular(2),
                        ),
                      ),
                    ),
                  ),
                ),
            ],
          ),
        ),
        pw.SizedBox(height: 4),
        pw.Row(
          children: [
            for (final month in months)
              pw.Expanded(
                child: pw.Center(
                  child: pw.Text(_monthFormat.format(month.month), style: pw.TextStyle(fontSize: 9, color: _textFaint)),
                ),
              ),
          ],
        ),
        pw.SizedBox(height: 10),
      ],
      pw.TableHelper.fromTextArray(
        headers: ['Month', 'Fills', 'Gallons', 'Spent', 'Avg/gal'],
        data: [
          for (final month in months)
            [
              _monthHeadingFormat.format(month.month),
              month.fillCount.toString(),
              month.totalGallons.toStringAsFixed(3),
              _currencyFormat.format(month.totalCost),
              _currencyFormat.format(month.avgPricePerGallon),
            ],
        ],
        cellAlignments: const {
          1: pw.Alignment.centerRight,
          2: pw.Alignment.centerRight,
          3: pw.Alignment.centerRight,
          4: pw.Alignment.centerRight,
        },
        headerAlignments: const {
          1: pw.Alignment.centerRight,
          2: pw.Alignment.centerRight,
          3: pw.Alignment.centerRight,
          4: pw.Alignment.centerRight,
        },
        headerStyle: pw.TextStyle(fontWeight: pw.FontWeight.bold, fontSize: 10, color: _textMuted),
        cellStyle: const pw.TextStyle(fontSize: 10),
        cellPadding: const pw.EdgeInsets.symmetric(horizontal: 8, vertical: 6),
        border: _tableBorder,
        headerDecoration: _tableHeaderDecoration,
        rowDecoration: _tableEvenRowDecoration,
        oddRowDecoration: _tableOddRowDecoration,
      ),
      if (months.length > 1) ...[
        pw.SizedBox(height: 6),
        pw.Row(
          mainAxisAlignment: pw.MainAxisAlignment.spaceBetween,
          children: [
            pw.Text('Total', style: pw.TextStyle(fontWeight: pw.FontWeight.bold, fontSize: 10)),
            pw.Text(
              '${report.fillCount} · ${report.totalGallons.toStringAsFixed(3)} gal · '
              '${_currencyFormat.format(report.totalCost)} · ${_currencyFormat.format(report.avgPricePerGallon)}',
              style: pw.TextStyle(fontWeight: pw.FontWeight.bold, fontSize: 10),
            ),
          ],
        ),
      ],
    ],
  );
}

pw.Widget _buildVehicleSection(FuelReport report) {
  return pw.Column(
    crossAxisAlignment: pw.CrossAxisAlignment.start,
    children: [
      pw.Text('By vehicle', style: pw.TextStyle(fontSize: 11, color: _textMuted)),
      for (final row in report.rows)
        pw.Container(
          padding: const pw.EdgeInsets.symmetric(vertical: 10),
          decoration: pw.BoxDecoration(border: pw.Border(top: pw.BorderSide(color: _borderLight, width: 0.5))),
          child: pw.Row(
            crossAxisAlignment: pw.CrossAxisAlignment.center,
            children: [
              pw.Expanded(
                flex: 2,
                child: pw.Column(
                  crossAxisAlignment: pw.CrossAxisAlignment.start,
                  children: [
                    pw.Text(row.vehicle.displayLabel, style: pw.TextStyle(fontSize: 14, fontWeight: pw.FontWeight.bold)),
                    pw.Text(row.vehicle.vin, style: pw.TextStyle(fontSize: 9, color: _textFaint)),
                  ],
                ),
              ),
              pw.Expanded(
                child: pw.Text(
                  '${row.entryCount} fill${row.entryCount == 1 ? '' : 's'}',
                  textAlign: pw.TextAlign.right,
                  style: pw.TextStyle(fontSize: 11, color: _textMuted),
                ),
              ),
              pw.Expanded(
                child: pw.Text(
                  _currencyFormat.format(row.totalCost),
                  textAlign: pw.TextAlign.right,
                  style: const pw.TextStyle(fontSize: 11),
                ),
              ),
              pw.Expanded(
                child: pw.Text(
                  '${row.totalGallons.toStringAsFixed(3)} gal',
                  textAlign: pw.TextAlign.right,
                  style: pw.TextStyle(fontSize: 14, fontWeight: pw.FontWeight.bold, color: _accentGreenDark),
                ),
              ),
            ],
          ),
        ),
    ],
  );
}

/// Item numbers (when both [includeLineItems] and [includeReceiptImages]
/// are on) are assigned once, in report order — vehicle by vehicle,
/// oldest-entry-first within each — and reused by both the "Line Items"
/// table and the "Receipt Images" section below it, so a photo and its
/// line item carry the same number despite living in separate sections.
List<pw.Widget> _buildLineItemsAndImagesSections(
  FuelReport report, {
  required bool includeLineItems,
  required bool includeReceiptImages,
  required Map<String, Uint8List> receiptImages,
}) {
  final showItemNumbers = includeLineItems && includeReceiptImages;
  final itemNumbers = <String, int>{};
  var nextNumber = 1;
  for (final row in report.rows) {
    for (final entry in row.entries) {
      itemNumbers[entry.id] = nextNumber++;
    }
  }

  final widgets = <pw.Widget>[];

  if (includeLineItems) {
    widgets.add(pw.Text('Line Items', style: _sectionHeadingStyle));
    for (final row in report.rows) {
      widgets.add(pw.SizedBox(height: 14));
      widgets.add(_buildVehicleSubheading(row));
      widgets.add(pw.SizedBox(height: 6));
      widgets.add(_buildLineItemsTable(row, showItemNumbers: showItemNumbers, itemNumbers: itemNumbers));
    }
  }

  if (includeReceiptImages) {
    final rowsWithImages = report.rows.where((row) => row.entries.any((e) => receiptImages.containsKey(e.id)));
    if (rowsWithImages.isNotEmpty) {
      if (includeLineItems) widgets.add(pw.SizedBox(height: 26));
      widgets.add(pw.Text('Receipt Images', style: _sectionHeadingStyle));
      for (final row in rowsWithImages) {
        widgets.add(pw.SizedBox(height: 14));
        widgets.add(_buildVehicleSubheading(row));
        widgets.add(pw.SizedBox(height: 8));
        widgets.add(_buildReceiptImagesWrap(
          row,
          receiptImages,
          showItemNumbers: showItemNumbers,
          itemNumbers: itemNumbers,
        ));
      }
    }
  }

  return widgets;
}

pw.Widget _buildVehicleSubheading(VehicleReportRow row) {
  return pw.Column(
    crossAxisAlignment: pw.CrossAxisAlignment.start,
    children: [
      pw.Text(row.vehicle.displayLabel, style: pw.TextStyle(fontSize: 12, fontWeight: pw.FontWeight.bold)),
      pw.Text('VIN: ${row.vehicle.vin}', style: pw.TextStyle(fontSize: 9, color: _textFaint)),
    ],
  );
}

pw.Widget _buildLineItemsTable(
  VehicleReportRow row, {
  required bool showItemNumbers,
  required Map<String, int> itemNumbers,
}) {
  return pw.TableHelper.fromTextArray(
    headers: [
      if (showItemNumbers) '#',
      'Date',
      'Gallons',
      'Price/Gal',
      'Total Cost',
    ],
    data: [
      for (final entry in row.entries)
        [
          if (showItemNumbers) itemNumbers[entry.id].toString(),
          _dateTimeFormat.format(entry.date),
          entry.gallons.toStringAsFixed(3),
          _currencyFormat.format(entry.pricePerGallon),
          _currencyFormat.format(entry.totalCost),
        ],
    ],
    cellAlignments: showItemNumbers
        ? const {
            0: pw.Alignment.centerLeft,
            2: pw.Alignment.centerRight,
            3: pw.Alignment.centerRight,
            4: pw.Alignment.centerRight,
          }
        : const {
            1: pw.Alignment.centerRight,
            2: pw.Alignment.centerRight,
            3: pw.Alignment.centerRight,
          },
    headerStyle: pw.TextStyle(fontWeight: pw.FontWeight.bold, fontSize: 10, color: _textMuted),
    cellStyle: const pw.TextStyle(fontSize: 10),
    cellPadding: const pw.EdgeInsets.symmetric(horizontal: 8, vertical: 6),
    border: _tableBorder,
    headerDecoration: _tableHeaderDecoration,
    rowDecoration: _tableEvenRowDecoration,
    oddRowDecoration: _tableOddRowDecoration,
  );
}

/// 140×140 — comfortably legible (the previous design's inline thumbnails,
/// at ~34×44, were too small to make out) while still fitting several per
/// row on a letter-width page.
const _receiptImageSize = 140.0;

pw.Widget _buildReceiptImagesWrap(
  VehicleReportRow row,
  Map<String, Uint8List> receiptImages, {
  required bool showItemNumbers,
  required Map<String, int> itemNumbers,
}) {
  return pw.Wrap(
    spacing: 10,
    runSpacing: 10,
    children: [
      for (final entry in row.entries)
        if (receiptImages[entry.id] case final bytes?)
          pw.Column(
            children: [
              pw.Container(
                width: _receiptImageSize,
                height: _receiptImageSize,
                decoration: pw.BoxDecoration(
                  color: _cardBackground,
                  borderRadius: const pw.BorderRadius.all(pw.Radius.circular(6)),
                  border: pw.Border.all(color: _borderLight, width: 0.5),
                ),
                child: pw.ClipRRect(
                  horizontalRadius: 6,
                  verticalRadius: 6,
                  child: pw.Image(pw.MemoryImage(bytes), fit: pw.BoxFit.cover),
                ),
              ),
              pw.SizedBox(height: 4),
              pw.Text(
                showItemNumbers
                    ? '#${itemNumbers[entry.id]} · ${_dayMonthFormat.format(entry.date)}'
                    : _dayMonthFormat.format(entry.date),
                style: pw.TextStyle(fontSize: 9, color: _textMuted),
              ),
            ],
          ),
    ],
  );
}

/// `fuel-report-<start>-<end>.pdf`, e.g. `fuel-report-20260101-20260331.pdf`.
String fuelReportFileName(FuelReport report) {
  final fmt = DateFormat('yyyyMMdd');
  return 'fuel-report-${fmt.format(report.startDate)}-${fmt.format(report.endDate)}.pdf';
}