import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:go_router/go_router.dart';

import '../../../core/router/app_router.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 '../../../core/widgets/primary_button.dart';
import '../../../domain/entities/shift_report.dart';
import '../../../domain/entities/transaction.dart';
import '../../auth/providers/auth_controller.dart';
import '../../payment/screens/payment_screen.dart' show methodIcon;
import '../../pos/providers/cart_controller.dart';
import '../../pos/providers/catalog_providers.dart';
import '../../pos/providers/navigation_provider.dart';
import '../../sync/providers/sync_controller.dart';

/// Closing the till.
///
/// Three things have to happen at the end of a shift and they have to happen
/// in this order: count what is physically in the drawer, compare it against
/// what the terminal says was taken in cash, then push the day up and hand the
/// terminal back. Doing it as a dialog meant the count was a single guessed
/// number typed into a box; a shift is worth its own screen.
///
/// The variance is the whole point. A till that is short is worth knowing
/// about while the person who worked it is still standing there.
class EndShiftScreen extends ConsumerStatefulWidget {
  const EndShiftScreen({super.key});

  /// Below this the two columns stack.
  static const double twoColumnAbove = 1000;

  @override
  ConsumerState<EndShiftScreen> createState() => _EndShiftScreenState();
}

/// What a till drawer actually holds, largest first.
const _denominations = <int>[2000, 500, 200, 100, 50, 20, 10, 5, 2, 1];

class _EndShiftScreenState extends ConsumerState<EndShiftScreen> {
  /// Note or coin value → how many were counted.
  final Map<int, int> _counted = {};

  final _openingFloat = TextEditingController(text: '0');
  bool _pushing = false;
  String? _error;

  @override
  void dispose() {
    _openingFloat.dispose();
    super.dispose();
  }

  double get _countedTotal => _counted.entries
      .fold(0.0, (sum, e) => sum + e.key * e.value);

  double get _float => double.tryParse(_openingFloat.text.trim()) ?? 0;

  int get _noteCount => _counted.values.fold(0, (sum, n) => sum + n);

  void _set(int denomination, int count) {
    setState(() {
      if (count <= 0) {
        _counted.remove(denomination);
      } else {
        _counted[denomination] = count;
      }
    });
  }

  /// Cash the terminal believes was taken, from the tender records — not from
  /// the bill totals, which include card and UPI.
  double _cashTaken(ShiftReport? report) =>
      report?.paymentBreakdown[PaymentMethod.cash] ?? 0;

  /// Pushes what is still held, then ends the session and clears the terminal.
  Future<void> _finish({required bool sync}) async {
    setState(() {
      _pushing = true;
      _error = null;
    });

    if (sync) {
      final outcome = await ref.read(orderSyncProvider.notifier).run();
      if (!mounted) return;
      if (!outcome.isSuccess) {
        setState(() {
          _pushing = false;
          _error = outcome.error ??
              'Upload failed. Every bill is still stored on this terminal.';
        });
        return;
      }
    }

    ref.read(cartControllerProvider.notifier).reset();

    // The real end of shift: the catalogue goes with it, so the next person
    // bills against a fresh import rather than this morning's prices.
    await ref.read(authControllerProvider.notifier).signOut();

    ref.read(catalogueVersionProvider.notifier).state++;
    ref.invalidate(allProductsProvider);
    ref.invalidate(visibleProductsProvider);
    ref.invalidate(categoryCountsProvider);
    ref.invalidate(lowStockProductsProvider);

    ref.read(activeModuleProvider.notifier).state = PosModule.pos;
    ref.read(searchQueryProvider.notifier).state = '';
    ref.read(selectedCategoryProvider.notifier).state = null;

    if (!mounted) return;
    context.go(AppRoutes.login);
  }

  @override
  Widget build(BuildContext context) {
    final report = ref.watch(myShiftReportProvider).value;
    final pending = ref.watch(unsyncedCountProvider).value ?? 0;
    final user = ref.watch(currentUserProvider);

    final cashTaken = _cashTaken(report);
    final expected = _float + cashTaken;
    final variance = _countedTotal - expected;

    return Scaffold(
      backgroundColor: AppColors.background,
      appBar: AppBar(
        title: const Text('End shift'),
        leading: IconButton(
          icon: const Icon(Icons.arrow_back_rounded),
          onPressed: _pushing ? null : () => context.pop(),
          tooltip: 'Back to the till',
        ),
      ),
      body: LayoutBuilder(
        builder: (context, box) {
          final twoColumn = box.maxWidth >= EndShiftScreen.twoColumnAbove;
          final pad = box.maxWidth < 700 ? AppSpacing.lg : AppSpacing.xxl;

          final count = _CountPanel(
            counted: _counted,
            openingFloat: _openingFloat,
            enabled: !_pushing,
            total: _countedTotal,
            noteCount: _noteCount,
            onChanged: _set,
            onFloatChanged: () => setState(() {}),
          );

          final review = _ReviewPanel(
            report: report,
            user: user?.name,
            openingFloat: _float,
            cashTaken: cashTaken,
            expected: expected,
            counted: _countedTotal,
            variance: variance,
            pending: pending,
            error: _error,
          );

          final minHeight = box.maxHeight.isFinite
              ? (box.maxHeight - pad * 2).clamp(0.0, double.infinity)
              : 0.0;

          return SingleChildScrollView(
            padding: EdgeInsets.all(pad),
            child: ConstrainedBox(
              constraints: BoxConstraints(minHeight: minHeight),
              child: Center(
                child: ConstrainedBox(
                  constraints: const BoxConstraints(maxWidth: 1240),
                  child: twoColumn
                      ? Row(
                          crossAxisAlignment: CrossAxisAlignment.start,
                          children: [
                            Expanded(child: count),
                            const SizedBox(width: AppSpacing.lg),
                            Expanded(child: review),
                          ],
                        )
                      : Column(
                          crossAxisAlignment: CrossAxisAlignment.stretch,
                          children: [
                            count,
                            const SizedBox(height: AppSpacing.lg),
                            review,
                          ],
                        ),
                ),
              ),
            ),
          );
        },
      ),
      bottomNavigationBar: _bottomBar(pending, variance),
    );
  }

  Widget _bottomBar(int pending, double variance) {
    final counted = _noteCount > 0;
    final short = variance < -0.5;
    final over = variance > 0.5;

    // The gate. A shift closes on a drawer that reconciles and on nothing
    // else — an uncounted or mismatched till is settled at the counter, with
    // the person who worked it still there, not discovered by the back office
    // the next morning.
    final balanced = counted && !short && !over;

    return SafeArea(
      child: Container(
        padding: const EdgeInsets.fromLTRB(
          AppSpacing.xxl,
          AppSpacing.md,
          AppSpacing.xxl,
          AppSpacing.lg,
        ),
        decoration: const BoxDecoration(
          color: AppColors.surface,
          border: Border(top: BorderSide(color: AppColors.border)),
        ),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Row(
              children: [
                Icon(
                  counted
                      ? (short || over
                          ? Icons.error_outline_rounded
                          : Icons.check_circle_outline_rounded)
                      : Icons.info_outline_rounded,
                  size: 16,
                  color: !counted
                      ? AppColors.textTertiary
                      : (short
                          ? AppColors.danger
                          : (over ? AppColors.warning : AppColors.success)),
                ),
                const SizedBox(width: AppSpacing.sm),
                Expanded(
                  child: Text(
                    !counted
                        ? 'Count the drawer. The shift cannot be ended until '
                            'it matches the expected amount.'
                        : short
                            ? 'The drawer is '
                                '${Formatters.money(variance.abs())} short. '
                                'Recount, or settle the difference — the '
                                'shift cannot be ended while it is off.'
                            : over
                                ? 'The drawer is '
                                    '${Formatters.money(variance)} over. '
                                    'Recount — the shift cannot be ended '
                                    'while it is off.'
                                : 'The drawer matches what was rung. Ready to '
                                    'end the shift.',
                    style: const TextStyle(
                      fontSize: 12.5,
                      color: AppColors.textSecondary,
                    ),
                  ),
                ),
              ],
            ),
            const SizedBox(height: AppSpacing.sm),
            PrimaryButton(
              label: !balanced
                  ? 'Drawer must match to end shift'
                  : pending > 0
                      ? 'Upload $pending bill(s) & end shift'
                      : 'End shift',
              icon: balanced ? Icons.logout_rounded : Icons.lock_outline_rounded,
              large: true,
              busy: _pushing,
              onPressed: (_pushing || !balanced)
                  ? null
                  : () => _finish(sync: pending > 0),
            ),
            if (pending > 0) ...[
              const SizedBox(height: AppSpacing.xs),
              TextButton(
                // Skipping the upload is still allowed; skipping the count is
                // not, so this is gated on the same condition.
                onPressed:
                    (_pushing || !balanced) ? null : () => _finish(sync: false),
                style: TextButton.styleFrom(
                  foregroundColor: AppColors.textSecondary,
                ),
                child: const Text('End shift without uploading'),
              ),
            ],
          ],
        ),
      ),
    );
  }
}

// ------------------------------------------------------------------- Count
class _CountPanel extends StatelessWidget {
  const _CountPanel({
    required this.counted,
    required this.openingFloat,
    required this.enabled,
    required this.total,
    required this.noteCount,
    required this.onChanged,
    required this.onFloatChanged,
  });

  final Map<int, int> counted;
  final TextEditingController openingFloat;
  final bool enabled;
  final double total;
  final int noteCount;
  final void Function(int denomination, int count) onChanged;
  final VoidCallback onFloatChanged;

  @override
  Widget build(BuildContext context) {
    return _Panel(
      title: 'Count the drawer',
      subtitle: 'Tap the notes and coins you are holding. Nothing is '
          'submitted until you end the shift.',
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        mainAxisSize: MainAxisSize.min,
        children: [
          TextField(
            controller: openingFloat,
            enabled: enabled,
            keyboardType: TextInputType.number,
            inputFormatters: [FilteringTextInputFormatter.digitsOnly],
            onChanged: (_) => onFloatChanged(),
            decoration: const InputDecoration(
              labelText: 'Opening float',
              helperText: 'What was in the drawer before trading started',
              prefixText: '₹ ',
              isDense: true,
            ),
          ),
          const SizedBox(height: AppSpacing.lg),
          const Divider(height: 1),
          const SizedBox(height: AppSpacing.sm),

          for (final value in _denominations)
            _DenominationRow(
              value: value,
              count: counted[value] ?? 0,
              enabled: enabled,
              onChanged: (n) => onChanged(value, n),
            ),

          const SizedBox(height: AppSpacing.sm),
          const Divider(height: 1),
          const SizedBox(height: AppSpacing.md),
          Row(
            children: [
              Expanded(
                child: Text(
                  noteCount == 0
                      ? 'Counted so far'
                      : 'Counted so far · $noteCount piece(s)',
                  style: const TextStyle(
                    fontSize: 13.5,
                    fontWeight: FontWeight.w600,
                    color: AppColors.textSecondary,
                  ),
                ),
              ),
              Text(
                Formatters.money(total),
                style: AppTypography.money(20, color: AppColors.textPrimary),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

class _DenominationRow extends StatelessWidget {
  const _DenominationRow({
    required this.value,
    required this.count,
    required this.enabled,
    required this.onChanged,
  });

  final int value;
  final int count;
  final bool enabled;
  final ValueChanged<int> onChanged;

  @override
  Widget build(BuildContext context) {
    final subtotal = value * count;
    final active = count > 0;

    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 3),
      child: Row(
        children: [
          SizedBox(
            width: 74,
            child: Text(
              '₹$value',
              style: AppTypography.money(
                15,
                color: active ? AppColors.textPrimary : AppColors.textTertiary,
              ),
            ),
          ),
          const Text(
            '×',
            style: TextStyle(fontSize: 12, color: AppColors.textTertiary),
          ),
          const SizedBox(width: AppSpacing.sm),
          _Stepper(
            count: count,
            enabled: enabled,
            onChanged: onChanged,
          ),
          const Spacer(),
          Text(
            active ? Formatters.money(subtotal.toDouble()) : '—',
            style: AppTypography.money(
              14,
              color: active ? AppColors.textPrimary : AppColors.textTertiary,
            ),
          ),
        ],
      ),
    );
  }
}

class _Stepper extends StatelessWidget {
  const _Stepper({
    required this.count,
    required this.enabled,
    required this.onChanged,
  });

  final int count;
  final bool enabled;
  final ValueChanged<int> onChanged;

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(
        color: AppColors.surface,
        borderRadius: AppRadius.brSm,
        border: Border.all(color: AppColors.border),
      ),
      child: Row(
        mainAxisSize: MainAxisSize.min,
        children: [
          _btn(
            Icons.remove_rounded,
            enabled && count > 0 ? () => onChanged(count - 1) : null,
          ),
          Container(
            constraints: const BoxConstraints(minWidth: 38),
            alignment: Alignment.center,
            child: Text('$count', style: AppTypography.money(14.5)),
          ),
          _btn(
            Icons.add_rounded,
            enabled ? () => onChanged(count + 1) : null,
          ),
        ],
      ),
    );
  }

  Widget _btn(IconData icon, VoidCallback? onTap) => Material(
        color: Colors.transparent,
        child: InkWell(
          onTap: onTap,
          borderRadius: AppRadius.brSm,
          child: SizedBox(
            width: 32,
            height: 32,
            child: Icon(
              icon,
              size: 16,
              color: onTap == null
                  ? AppColors.textTertiary.withValues(alpha: 0.5)
                  : AppColors.primary,
            ),
          ),
        ),
      );
}

// ------------------------------------------------------------------ Review
class _ReviewPanel extends StatelessWidget {
  const _ReviewPanel({
    required this.report,
    required this.user,
    required this.openingFloat,
    required this.cashTaken,
    required this.expected,
    required this.counted,
    required this.variance,
    required this.pending,
    required this.error,
  });

  final ShiftReport? report;
  final String? user;
  final double openingFloat;
  final double cashTaken;
  final double expected;
  final double counted;
  final double variance;
  final int pending;
  final String? error;

  @override
  Widget build(BuildContext context) {
    final short = variance < -0.5;
    final over = variance > 0.5;
    final tone = counted == 0
        ? AppColors.textTertiary
        : (short ? AppColors.danger : (over ? AppColors.warning
            : AppColors.success));

    return Column(
      crossAxisAlignment: CrossAxisAlignment.stretch,
      mainAxisSize: MainAxisSize.min,
      children: [
        _Panel(
          title: 'Cash drawer',
          subtitle: 'What the terminal expects, against what you counted.',
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            mainAxisSize: MainAxisSize.min,
            children: [
              _row('Opening float', Formatters.money(openingFloat)),
              _row('Cash sales today', Formatters.money(cashTaken)),
              const Divider(height: AppSpacing.xl),
              _row(
                'Expected in drawer',
                Formatters.money(expected),
                strong: true,
              ),
              _row('You counted', Formatters.money(counted)),
              const SizedBox(height: AppSpacing.md),
              Container(
                padding: const EdgeInsets.all(AppSpacing.md),
                decoration: BoxDecoration(
                  color: counted == 0
                      ? AppColors.surfaceAlt
                      : (short
                          ? AppColors.dangerSurface
                          : (over
                              ? AppColors.warningSurface
                              : AppColors.successSurface)),
                  borderRadius: AppRadius.brMd,
                ),
                child: Row(
                  children: [
                    Expanded(
                      child: Text(
                        counted == 0
                            ? 'Not counted yet'
                            : (short
                                ? 'Short'
                                : (over ? 'Over' : 'Balanced')),
                        style: TextStyle(
                          fontSize: 14,
                          fontWeight: FontWeight.w700,
                          color: tone,
                        ),
                      ),
                    ),
                    Text(
                      counted == 0
                          ? '—'
                          : '${variance >= 0 ? '+' : '−'}'
                              '${Formatters.money(variance.abs())}',
                      style: AppTypography.money(20, color: tone),
                    ),
                  ],
                ),
              ),
            ],
          ),
        ),
        const SizedBox(height: AppSpacing.lg),

        _Panel(
          title: 'Today at this till',
          subtitle: user == null ? null : 'Rung by $user',
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            mainAxisSize: MainAxisSize.min,
            children: [
              _row('Bills', '${report?.billCount ?? 0}'),
              _row('Items sold',
                  (report?.itemCount ?? 0).toStringAsFixed(0),),
              _row('Gross sales',
                  Formatters.money(report?.grossSales ?? 0),),
              _row('GST collected',
                  Formatters.money(report?.taxCollected ?? 0),),
              if ((report?.paymentBreakdown ?? const {}).isNotEmpty) ...[
                const Divider(height: AppSpacing.xl),
                for (final e in report!.paymentBreakdown.entries)
                  Padding(
                    padding: const EdgeInsets.symmetric(vertical: 3),
                    child: Row(
                      children: [
                        Icon(methodIcon(e.key),
                            size: 16, color: AppColors.textSecondary,),
                        const SizedBox(width: AppSpacing.sm),
                        Expanded(
                          child: Text(
                            e.key.label,
                            style: const TextStyle(
                              fontSize: 13.5,
                              color: AppColors.textSecondary,
                            ),
                          ),
                        ),
                        Text(Formatters.money(e.value),
                            style: AppTypography.money(13.5),),
                      ],
                    ),
                  ),
              ],
            ],
          ),
        ),
        const SizedBox(height: AppSpacing.lg),

        _Panel(
          title: 'Before you hand it over',
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            mainAxisSize: MainAxisSize.min,
            children: [
              _checkRow(
                pending == 0,
                pending == 0
                    ? 'Every bill has been uploaded.'
                    : '$pending bill(s) still on this terminal — they upload '
                        'when you end the shift.',
              ),
              _checkRow(
                !short && !over && counted > 0,
                counted == 0
                    ? 'Drawer not counted yet — required before the shift can '
                        'be ended.'
                    : (short || over)
                        ? 'Drawer does not match the expected amount. The '
                            'shift stays open until it does.'
                        : 'Drawer matches the expected amount.',
              ),
              _checkRow(
                false,
                'Products are removed from this terminal at the end of a '
                'shift. An admin imports them again tomorrow.',
                neutral: true,
              ),
              if (error != null) ...[
                const SizedBox(height: AppSpacing.md),
                Container(
                  padding: const EdgeInsets.all(AppSpacing.md),
                  decoration: const BoxDecoration(
                    color: AppColors.dangerSurface,
                    borderRadius: AppRadius.brSm,
                  ),
                  child: Row(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: [
                      const Icon(Icons.wifi_off_rounded,
                          size: 18, color: AppColors.danger,),
                      const SizedBox(width: AppSpacing.sm),
                      Expanded(
                        child: Text(
                          error!,
                          style: const TextStyle(
                            fontSize: 12.5,
                            color: AppColors.danger,
                            height: 1.45,
                          ),
                        ),
                      ),
                    ],
                  ),
                ),
              ],
            ],
          ),
        ),
      ],
    );
  }

  Widget _row(String label, String value, {bool strong = false}) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 3),
        child: Row(
          children: [
            Expanded(
              child: Text(
                label,
                style: TextStyle(
                  fontSize: strong ? 14 : 13.5,
                  fontWeight: strong ? FontWeight.w600 : FontWeight.w400,
                  color: strong
                      ? AppColors.textPrimary
                      : AppColors.textSecondary,
                ),
              ),
            ),
            Text(
              value,
              style: AppTypography.money(
                strong ? 16 : 13.5,
                color: strong ? AppColors.primary : null,
              ),
            ),
          ],
        ),
      );

  Widget _checkRow(bool done, String text, {bool neutral = false}) => Padding(
        padding: const EdgeInsets.symmetric(vertical: 4),
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            Icon(
              neutral
                  ? Icons.info_outline_rounded
                  : (done
                      ? Icons.check_circle_outline_rounded
                      : Icons.radio_button_unchecked_rounded),
              size: 16,
              color: neutral
                  ? AppColors.textTertiary
                  : (done ? AppColors.success : AppColors.textTertiary),
            ),
            const SizedBox(width: AppSpacing.sm),
            Expanded(
              child: Text(
                text,
                style: const TextStyle(
                  fontSize: 12.5,
                  color: AppColors.textSecondary,
                  height: 1.5,
                ),
              ),
            ),
          ],
        ),
      );
}

/// One card shape for every block on this screen, so the two columns line up
/// row for row instead of each panel inventing its own padding.
class _Panel extends StatelessWidget {
  const _Panel({
    required this.title,
    required this.child,
    this.subtitle,
  });

  final String title;
  final String? subtitle;
  final Widget child;

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: const EdgeInsets.all(AppSpacing.xl),
      decoration: BoxDecoration(
        color: AppColors.surface,
        borderRadius: AppRadius.brXl,
        border: Border.all(color: AppColors.border),
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        mainAxisSize: MainAxisSize.min,
        children: [
          Text(
            title,
            style: const TextStyle(
              fontSize: 16,
              fontWeight: FontWeight.w600,
              letterSpacing: -0.2,
              color: AppColors.textPrimary,
            ),
          ),
          if (subtitle != null) ...[
            const SizedBox(height: 2),
            Text(
              subtitle!,
              style: const TextStyle(
                fontSize: 12.5,
                color: AppColors.textSecondary,
                height: 1.45,
              ),
            ),
          ],
          const SizedBox(height: AppSpacing.lg),
          child,
        ],
      ),
    );
  }
}