import 'package:flutter/material.dart';

import '../../../core/constants/app_constants.dart';
import '../../../core/theme/app_colors.dart';
import '../../../core/theme/app_dimens.dart';
import '../../../core/theme/app_typography.dart';
import '../../../core/utils/formatters.dart';
import '../../../domain/entities/cart.dart';
import '../../../domain/entities/transaction.dart';

/// Paper-like preview of what the thermal printer produced.
class ReceiptPreview extends StatelessWidget {
  const ReceiptPreview({super.key, required this.transaction});

  final SaleTransaction transaction;

  /// Groups the bill by GST rate, mirroring how the printed invoice lists it.
  List<_PreviewSlab> _slabs(SaleTransaction txn) {
    final cart = txn.cart;
    final factor = cart.subtotal <= 0 ? 1.0 : cart.netAmount / cart.subtotal;

    final grouped = <double, List<CartLine>>{};
    for (final line in cart.lines) {
      grouped.putIfAbsent(line.product.gstRate, () => []).add(line);
    }

    final rates = grouped.keys.toList()..sort();
    return [
      for (var i = 0; i < rates.length; i++)
        _PreviewSlab(i + 1, rates[i], grouped[rates[i]]!, factor),
    ];
  }

  double _gross(SaleTransaction txn) => txn.cart.lines
      .fold(0.0, (s, l) => s + (l.product.mrp ?? l.product.price) * l.quantity);

  @override
  Widget build(BuildContext context) {
    final txn = transaction;
    final cart = txn.cart;
    final slabs = _slabs(txn);
    final gross = _gross(txn);
    final discount = gross - cart.netAmount;

    return Container(
      decoration: const BoxDecoration(
        color: AppColors.surface,
        borderRadius: AppRadius.brLg,
        boxShadow: AppColors.shadowMd,
      ),
      child: Column(children: [
        const _Perforation(top: true),
        Expanded(
          child: SingleChildScrollView(
            padding: const EdgeInsets.symmetric(
              horizontal: AppSpacing.xl,
              vertical: AppSpacing.lg,
            ),
            child: DefaultTextStyle(
              style: AppTypography.mono(10, color: AppColors.textPrimary),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: [
                  // ------------------------------------------------ header
                  Center(
                    child: Column(children: [
                      Text(
                        AppConstants.storeName.toUpperCase(),
                        style: AppTypography.mono(15)
                            .copyWith(fontWeight: FontWeight.w700),
                      ),
                      Text(AppConstants.storeLegalName,
                          style: AppTypography.mono(8.5),),
                      const SizedBox(height: 2),
                      Text(AppConstants.storeAddress,
                          textAlign: TextAlign.center,
                          style: AppTypography.mono(8.5),),
                      Text('Customer care : ${AppConstants.storePhone}',
                          style: AppTypography.mono(8.5),),
                      Text('CIN No : ${AppConstants.storeCin}',
                          style: AppTypography.mono(8.5),),
                      Text('GSTIN : ${AppConstants.storeGstin}',
                          style: AppTypography.mono(8.5),),
                      Text('FSSAI Lic No : ${AppConstants.storeFssai}',
                          style: AppTypography.mono(8.5),),
                    ],),
                  ),

                  if (discount > 0) ...[
                    const SizedBox(height: AppSpacing.sm),
                    Center(
                      child: Text(
                        'You have saved Rs.${discount.toStringAsFixed(2)}',
                        style: AppTypography.mono(11).copyWith(
                          fontWeight: FontWeight.w700,
                          color: AppColors.textPrimary,
                        ),
                      ),
                    ),
                  ],

                  const _Dashes(),
                  Center(
                    child: Column(children: [
                      Text('TAX INVOICE',
                          style: AppTypography.mono(11)
                              .copyWith(fontWeight: FontWeight.w700),),
                      Text('xxxxxx Original for Recipient xxxxxx',
                          style: AppTypography.mono(8),),
                    ],),
                  ),
                  const SizedBox(height: AppSpacing.sm),

                  // -------------------------------------------------- meta
                  _plain('Place of Supply & State Code: '
                      '${AppConstants.stateCode} ${AppConstants.stateName}'),
                  _plain('Customer Type: '
                      '${txn.customer == null ? 'URD' : 'REG'}'),
                  _row('Date:${Formatters.receiptStamp(txn.createdAt)}',
                      'Bill No:${txn.invoiceNumber.split('-').last}',),
                  _row(
                    'Store:${AppConstants.storeCode} '
                        'Cashier:${txn.cashierName}',
                    'Pos:${AppConstants.posNumber}',
                  ),
                  if (txn.customer != null)
                    _plain('Customer: ${txn.customer!.name}  '
                        '${txn.customer!.mobile}'),

                  const _Dashes(),

                  // ------------------------------------------------- items
                  Row(children: [
                    Expanded(flex: 12, child: _bold('HSN')),
                    Expanded(flex: 34, child: _bold('Item Description')),
                    Expanded(
                        flex: 16,
                        child: _bold('Net Price', align: TextAlign.right),),
                    Expanded(
                        flex: 8, child: _bold('Qty', align: TextAlign.right),),
                    Expanded(
                        flex: 18,
                        child: _bold('Value', align: TextAlign.right),),
                  ],),
                  const SizedBox(height: 3),

                  for (final slab in slabs) ...[
                    Padding(
                      padding: const EdgeInsets.only(top: 5, bottom: 2),
                      child: Text(
                        '${slab.index}) CGST @ ${slab.halfPercent}  '
                        'SGST @ ${slab.halfPercent}',
                        style: AppTypography.mono(9).copyWith(
                          fontWeight: FontWeight.w700,
                          color: AppColors.textPrimary,
                        ),
                      ),
                    ),
                    for (final line in slab.lines)
                      Padding(
                        padding: const EdgeInsets.symmetric(vertical: 1.5),
                        child: Row(children: [
                          Expanded(
                              flex: 12,
                              child: _cell(line.product.hsnCode ?? '-'),),
                          Expanded(
                              flex: 34,
                              child:
                                  _cell(line.product.name.toUpperCase()),),
                          Expanded(
                            flex: 16,
                            child: _cell(
                                line.product.price.toStringAsFixed(2),
                                align: TextAlign.right,),
                          ),
                          Expanded(
                            flex: 8,
                            child: _cell(_qty(line.quantity),
                                align: TextAlign.right,),
                          ),
                          Expanded(
                            flex: 18,
                            child: _cell(line.payable.toStringAsFixed(2),
                                align: TextAlign.right,),
                          ),
                        ],),
                      ),
                  ],

                  const _Dashes(),

                  // ------------------------------------------------ totals
                  _row('Items:${cart.lineCount}',
                      'Qty:${_qty(cart.totalQuantity)}   '
                          '${cart.netAmount.toStringAsFixed(2)}'),
                  const SizedBox(height: 3),
                  _amount('Gross Sales Value', gross),
                  if (discount > 0) _amount('Total Discount', discount),
                  _amount(
                      'Net Sales Value (Inclusive of GST)', cart.netAmount,),
                  if (cart.roundOff != 0)
                    _amount('Round Off', cart.roundOff),
                  _amount('Total Amount Paid', txn.total, bold: true),
                  for (final p in txn.payments)
                    _amount(p.method.label.toUpperCase(), p.amount),
                  if (txn.changeDue > 0)
                    _amount('Change Returned', txn.changeDue),
                  Text('(AMOUNT INCLUSIVE OF APPLICABLE TAXES)',
                      style: AppTypography.mono(8),),

                  const SizedBox(height: AppSpacing.md),

                  // ------------------------------------------- gst breakup
                  Center(
                    child: Text('------GST Breakup Details------ Amount (INR)',
                        style: AppTypography.mono(8.5),),
                  ),
                  const SizedBox(height: 4),
                  Row(children: [
                    Expanded(flex: 10, child: _bold('GST')),
                    Expanded(
                        flex: 20,
                        child: _bold('Taxable', align: TextAlign.right),),
                    Expanded(
                        flex: 16,
                        child: _bold('CGST', align: TextAlign.right),),
                    Expanded(
                        flex: 16,
                        child: _bold('SGST', align: TextAlign.right),),
                    Expanded(
                        flex: 14,
                        child: _bold('CESS', align: TextAlign.right),),
                    Expanded(
                        flex: 20,
                        child: _bold('Total', align: TextAlign.right),),
                  ],),
                  const SizedBox(height: 2),
                  for (final s in slabs)
                    Padding(
                      padding: const EdgeInsets.symmetric(vertical: 1),
                      child: Row(children: [
                        Expanded(flex: 10, child: _cell('${s.index}')),
                        Expanded(
                            flex: 20,
                            child: _cell(s.taxable.toStringAsFixed(2),
                                align: TextAlign.right,),),
                        Expanded(
                            flex: 16,
                            child: _cell(s.cgst.toStringAsFixed(2),
                                align: TextAlign.right,),),
                        Expanded(
                            flex: 16,
                            child: _cell(s.sgst.toStringAsFixed(2),
                                align: TextAlign.right,),),
                        Expanded(
                            flex: 14,
                            child: _cell('0.00', align: TextAlign.right),),
                        Expanded(
                            flex: 20,
                            child: _cell(s.total.toStringAsFixed(2),
                                align: TextAlign.right,),),
                      ],),
                    ),
                  const _Dashes(),
                  Row(children: [
                    Expanded(flex: 10, child: _bold('Total')),
                    Expanded(
                        flex: 20,
                        child: _bold(
                            slabs
                                .fold(0.0, (a, s) => a + s.taxable)
                                .toStringAsFixed(2),
                            align: TextAlign.right,),),
                    Expanded(
                        flex: 16,
                        child: _bold(
                            slabs
                                .fold(0.0, (a, s) => a + s.cgst)
                                .toStringAsFixed(2),
                            align: TextAlign.right,),),
                    Expanded(
                        flex: 16,
                        child: _bold(
                            slabs
                                .fold(0.0, (a, s) => a + s.sgst)
                                .toStringAsFixed(2),
                            align: TextAlign.right,),),
                    Expanded(
                        flex: 14,
                        child: _bold('0.00', align: TextAlign.right),),
                    Expanded(
                        flex: 20,
                        child: _bold(
                            slabs
                                .fold(0.0, (a, s) => a + s.total)
                                .toStringAsFixed(2),
                            align: TextAlign.right,),),
                  ],),

                  const _Dashes(),
                  _plain('TaxInvoice# ${txn.invoiceNumber}'),
                  if (txn.customer != null)
                    _plain('Loyalty Pts: earned ${txn.pointsEarned}  '
                        'Bal: ${txn.customer!.loyaltyPoints - txn.pointsRedeemed + txn.pointsEarned}'),
                  _plain('Terms & Conditions Apply'),

                  const SizedBox(height: AppSpacing.lg),
                  Center(
                    child: Column(children: [
                      _FakeBarcode(value: txn.invoiceNumber),
                      const SizedBox(height: AppSpacing.sm),
                      Text('* Thank You for Shopping with us *',
                          style: AppTypography.mono(10)
                              .copyWith(fontWeight: FontWeight.w700),),
                      Text('Powered by Nearle POS',
                          style: AppTypography.mono(8),),
                    ],),
                  ),
                ],
              ),
            ),
          ),
        ),
        const _Perforation(top: false),
      ],),
    );
  }

  String _qty(double q) =>
      q % 1 == 0 ? q.toStringAsFixed(0) : q.toStringAsFixed(3);

  Widget _plain(String text) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 0.8),
        child: Text(text, style: AppTypography.mono(9)),
      );

  Widget _row(String left, String right) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 0.8),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            Flexible(
              child: Text(left,
                  overflow: TextOverflow.ellipsis,
                  style: AppTypography.mono(9),),
            ),
            const SizedBox(width: AppSpacing.sm),
            Text(right, style: AppTypography.mono(9)),
          ],
        ),
      );

  Widget _amount(String label, double value, {bool bold = false}) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 1),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            Flexible(
              child: Text(
                label,
                overflow: TextOverflow.ellipsis,
                style: AppTypography.mono(9.5).copyWith(
                  fontWeight: bold ? FontWeight.w700 : FontWeight.w400,
                  color: AppColors.textPrimary,
                ),
              ),
            ),
            const SizedBox(width: AppSpacing.sm),
            Text(
              value.toStringAsFixed(2),
              style: AppTypography.mono(9.5).copyWith(
                fontWeight: bold ? FontWeight.w700 : FontWeight.w400,
                color: AppColors.textPrimary,
              ),
            ),
          ],
        ),
      );

  Widget _bold(String text, {TextAlign align = TextAlign.left}) => Text(
        text,
        textAlign: align,
        maxLines: 1,
        overflow: TextOverflow.clip,
        style: AppTypography.mono(8.5).copyWith(
          fontWeight: FontWeight.w700,
          color: AppColors.textPrimary,
        ),
      );

  Widget _cell(String text, {TextAlign align = TextAlign.left}) => Text(
        text,
        textAlign: align,
        maxLines: 1,
        overflow: TextOverflow.ellipsis,
        style: AppTypography.mono(8.5),
      );
}

/// One GST rate's slice of the bill, for the preview.
class _PreviewSlab {
  const _PreviewSlab(this.index, this.rate, this.lines, this.factor);

  final int index;
  final double rate;
  final List<CartLine> lines;
  final double factor;

  String get halfPercent => '${(rate * 100 / 2).toStringAsFixed(2)}%';

  double get total => lines.fold(0.0, (s, l) => s + l.payable * factor);

  double get taxAmount => lines.fold(0.0, (s, l) => s + l.taxAmount * factor);

  double get taxable => total - taxAmount;

  double get cgst => taxAmount / 2;

  double get sgst => taxAmount - cgst;
}

class _Dashes extends StatelessWidget {
  const _Dashes();

  @override
  Widget build(BuildContext context) {
    return const Padding(
      padding: EdgeInsets.symmetric(vertical: AppSpacing.sm),
      child: Text(
        '- - - - - - - - - - - - - - - - - - - - - - - - - -',
        maxLines: 1,
        overflow: TextOverflow.clip,
        style: TextStyle(color: AppColors.textTertiary, fontSize: 10),
      ),
    );
  }
}

/// Zig-zag torn-paper edge.
class _Perforation extends StatelessWidget {
  const _Perforation({required this.top});

  final bool top;

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      height: 10,
      child: CustomPaint(
        size: const Size(double.infinity, 10),
        painter: _PerforationPainter(top: top),
      ),
    );
  }
}

class _PerforationPainter extends CustomPainter {
  const _PerforationPainter({required this.top});

  final bool top;

  @override
  void paint(Canvas canvas, Size size) {
    const tooth = 12.0;
    final path = Path();

    if (top) {
      path.moveTo(0, size.height);
      for (var x = 0.0; x < size.width; x += tooth) {
        path.lineTo(x + tooth / 2, 0);
        path.lineTo(x + tooth, size.height);
      }
      path.lineTo(size.width, size.height);
    } else {
      path.moveTo(0, 0);
      for (var x = 0.0; x < size.width; x += tooth) {
        path.lineTo(x + tooth / 2, size.height);
        path.lineTo(x + tooth, 0);
      }
      path.lineTo(size.width, 0);
    }
    path.close();

    canvas.drawPath(path, Paint()..color = AppColors.surface);
  }

  @override
  bool shouldRepaint(covariant _PerforationPainter oldDelegate) =>
      oldDelegate.top != top;
}

/// Decorative Code-128-style bar rendering for the preview only.
class _FakeBarcode extends StatelessWidget {
  const _FakeBarcode({required this.value});

  final String value;

  @override
  Widget build(BuildContext context) {
    final bars = value.codeUnits;

    return Column(children: [
      SizedBox(
        height: 38,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            for (var i = 0; i < bars.length * 2; i++)
              Container(
                width: (bars[i ~/ 2] % 3 == 0) ? 3 : 1.5,
                margin: const EdgeInsets.symmetric(horizontal: 0.7),
                color: i.isEven
                    ? AppColors.textPrimary
                    : Colors.transparent,
              ),
          ],
        ),
      ),
      const SizedBox(height: 3),
      Text(value, style: AppTypography.mono(9)),
    ],);
  }
}