/// Overview: monthly income/expense chart, summary cards, and day history.
library;

import 'package:fl_chart/fl_chart.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

import '../models/bank.dart';
import '../providers/bank_provider.dart';
import '../utils/helpers.dart';
import '../utils/navigation.dart';
import '../utils/tx_calendar.dart';
import '../widgets/empty_state.dart';
import '../widgets/loading_view.dart';
import '../widgets/responsive_body.dart';
import 'transactions_screen.dart';

class OverviewScreen extends StatefulWidget {
  const OverviewScreen({super.key});

  @override
  State<OverviewScreen> createState() => _OverviewScreenState();
}

class _OverviewScreenState extends State<OverviewScreen> {
  static const _chartMonths = 6;

  @override
  Widget build(BuildContext context) {
    final bank = context.watch<BankController>();

    return Scaffold(
      appBar: AppBar(
        title: const Text('Overview'),
        actions: bankAppBarActions(
          context: context,
          onRefresh: bank.refresh,
          refreshing: bank.isLoading,
        ),
      ),
      body: RefreshIndicator(
        onRefresh: bank.refresh,
        child: ResponsiveBody(
          child: _buildBody(context, bank),
        ),
      ),
    );
  }

  Widget _buildBody(BuildContext context, BankController bank) {
    final theme = Theme.of(context);
    final colors = theme.colorScheme;

    if (bank.isLoading && bank.transactions.isEmpty && bank.balance == null) {
      return const LoadingView(message: 'Loading overview…');
    }

    if (!bank.isLinked && !bank.hasData) {
      return ListView(
        physics: const AlwaysScrollableScrollPhysics(),
        children: const [
          EmptyState(
            icon: Icons.insights_outlined,
            title: 'No overview yet',
            message: 'Connect your bank on Home to see balance and charts.',
          ),
        ],
      );
    }

    final currency = bank.balance?.currency ??
        (bank.transactions.isNotEmpty
            ? bank.transactions.first.currency
            : 'EUR');
    final months = _lastMonths(_chartMonths);
    final monthly = _monthlyTotals(bank.transactions, months);
    final nowMonth = monthStart(DateTime.now());
    final current = monthly[nowMonth] ??
        const _MonthBucket(income: 0, expense: 0);
    final history = _monthHistory(bank.transactions);
    final incomeColor = colors.primary;
    final expenseColor = const Color(0xFF6FCF97);

    return ListView(
      physics: const AlwaysScrollableScrollPhysics(),
      padding: const EdgeInsets.fromLTRB(0, 8, 0, 32),
      children: [
        if (bank.error != null) ...[
          Text(
            bank.error!,
            style: theme.textTheme.bodyMedium?.copyWith(color: colors.error),
          ),
          const SizedBox(height: 12),
        ],
        _ChartCard(
          months: months,
          monthly: monthly,
          currency: currency,
          incomeColor: incomeColor,
          expenseColor: expenseColor,
        ),
        const SizedBox(height: 14),
        Row(
          children: [
            Expanded(
              child: _SummaryCard(
                icon: Icons.savings_outlined,
                iconBackground: incomeColor.withValues(alpha: 0.14),
                iconColor: incomeColor,
                amount: formatMoney(current.income, currency),
                label: 'Income',
              ),
            ),
            const SizedBox(width: 12),
            Expanded(
              child: _SummaryCard(
                icon: Icons.receipt_long_outlined,
                iconBackground: expenseColor.withValues(alpha: 0.18),
                iconColor: const Color(0xFF2F9E62),
                amount: formatMoney(current.expense, currency),
                label: 'Expenses',
              ),
            ),
          ],
        ),
        const SizedBox(height: 8),
        Text(
          formatMonthYear(nowMonth),
          style: theme.textTheme.labelMedium,
        ),
        const SizedBox(height: 20),
        Text('History', style: theme.textTheme.titleLarge),
        const SizedBox(height: 12),
        if (history.isEmpty)
          Text(
            'No monthly activity to show.',
            style: theme.textTheme.bodyMedium,
          )
        else
          for (final month in history) ...[
            _HistoryCard(
              month: month.month,
              income: month.income,
              expense: month.expense,
              currency: currency,
              onTap: () => _openMonth(context, month.month),
            ),
            const SizedBox(height: 10),
          ],
      ],
    );
  }

  void _openMonth(BuildContext context, DateTime month) {
    Navigator.of(context).push(
      MaterialPageRoute<void>(
        builder: (_) => TransactionsScreen(initialMonth: month),
      ),
    );
  }
}

class _MonthBucket {
  const _MonthBucket({required this.income, required this.expense});
  final double income;
  final double expense;
}

class _MonthHistoryRow {
  const _MonthHistoryRow({
    required this.month,
    required this.income,
    required this.expense,
  });
  final DateTime month;
  final double income;
  final double expense;
}

List<DateTime> _lastMonths(int count) {
  final now = monthStart(DateTime.now());
  return [
    for (var i = count - 1; i >= 0; i--) addMonths(now, -i),
  ];
}

DateTime? _txDate(BankTransaction tx) {
  final parsed = DateTime.tryParse(tx.date);
  return parsed == null ? null : dateOnly(parsed);
}

Map<DateTime, _MonthBucket> _monthlyTotals(
  List<BankTransaction> txs,
  List<DateTime> months,
) {
  final totals = {
    for (final month in months) month: (income: 0.0, expense: 0.0),
  };
  for (final tx in txs) {
    final date = _txDate(tx);
    if (date == null) continue;
    final key = monthStart(date);
    final current = totals[key];
    if (current == null) continue;
    if (tx.amount >= 0) {
      totals[key] = (income: current.income + tx.amount, expense: current.expense);
    } else {
      totals[key] = (
        income: current.income,
        expense: current.expense + tx.amount.abs(),
      );
    }
  }
  return {
    for (final e in totals.entries)
      e.key: _MonthBucket(income: e.value.income, expense: e.value.expense),
  };
}

/// Months that have activity, newest first.
List<_MonthHistoryRow> _monthHistory(List<BankTransaction> txs) {
  final map = <DateTime, ({double income, double expense})>{};
  for (final tx in txs) {
    final date = _txDate(tx);
    if (date == null) continue;
    final key = monthStart(date);
    final current = map[key] ?? (income: 0.0, expense: 0.0);
    if (tx.amount >= 0) {
      map[key] = (income: current.income + tx.amount, expense: current.expense);
    } else {
      map[key] = (
        income: current.income,
        expense: current.expense + tx.amount.abs(),
      );
    }
  }
  final keys = map.keys.toList()..sort((a, b) => b.compareTo(a));
  return [
    for (final key in keys)
      _MonthHistoryRow(
        month: key,
        income: map[key]!.income,
        expense: map[key]!.expense,
      ),
  ];
}

class _ChartCard extends StatelessWidget {
  const _ChartCard({
    required this.months,
    required this.monthly,
    required this.currency,
    required this.incomeColor,
    required this.expenseColor,
  });

  final List<DateTime> months;
  final Map<DateTime, _MonthBucket> monthly;
  final String currency;
  final Color incomeColor;
  final Color expenseColor;

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final colors = theme.colorScheme;
    var maxY = 0.0;
    for (final month in months) {
      final bucket = monthly[month]!;
      if (bucket.income > maxY) maxY = bucket.income;
      if (bucket.expense > maxY) maxY = bucket.expense;
    }
    final safeMax = maxY <= 0 ? 1.0 : maxY * 1.15;

    return Card(
      color: colors.surface,
      elevation: 0,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(24),
        side: BorderSide(color: colors.outlineVariant.withValues(alpha: 0.5)),
      ),
      child: Padding(
        padding: const EdgeInsets.fromLTRB(16, 14, 16, 16),
        child: Column(
          children: [
            Row(
              children: [
                Container(
                  padding:
                      const EdgeInsets.symmetric(horizontal: 12, vertical: 8),
                  decoration: BoxDecoration(
                    color: colors.surfaceContainerHighest.withValues(alpha: 0.55),
                    borderRadius: BorderRadius.circular(20),
                  ),
                  child: Row(
                    mainAxisSize: MainAxisSize.min,
                    children: [
                      Text('Monthly', style: theme.textTheme.labelLarge),
                      const SizedBox(width: 4),
                      Icon(
                        Icons.keyboard_arrow_down,
                        size: 18,
                        color: colors.onSurfaceVariant,
                      ),
                    ],
                  ),
                ),
                const Spacer(),
                _LegendDot(color: incomeColor, label: 'Income'),
                const SizedBox(width: 14),
                _LegendDot(color: expenseColor, label: 'Expense'),
              ],
            ),
            const SizedBox(height: 16),
            SizedBox(
              height: 220,
              child: months.every(
                (m) =>
                    monthly[m]!.income == 0 && monthly[m]!.expense == 0,
              )
                  ? Center(
                      child: Text(
                        'No income or expenses in this period',
                        style: theme.textTheme.bodyMedium,
                        textAlign: TextAlign.center,
                      ),
                    )
                  : BarChart(
                      BarChartData(
                        maxY: safeMax,
                        groupsSpace: 18,
                        barTouchData: BarTouchData(
                          touchTooltipData: BarTouchTooltipData(
                            getTooltipItem: (group, groupIndex, rod, rodIndex) {
                              final month = months[group.x.toInt()];
                              final bucket = monthly[month]!;
                              final isIncome = rodIndex == 1;
                              final value =
                                  isIncome ? bucket.income : bucket.expense;
                              return BarTooltipItem(
                                '${_shortMonth(month)}\n'
                                '${isIncome ? 'Income' : 'Expense'}\n'
                                '${formatMoney(value, currency)}',
                                TextStyle(color: colors.onInverseSurface),
                              );
                            },
                          ),
                        ),
                        titlesData: FlTitlesData(
                          topTitles: const AxisTitles(
                            sideTitles: SideTitles(showTitles: false),
                          ),
                          rightTitles: const AxisTitles(
                            sideTitles: SideTitles(showTitles: false),
                          ),
                          leftTitles: AxisTitles(
                            sideTitles: SideTitles(
                              showTitles: true,
                              reservedSize: 42,
                              interval: safeMax / 3,
                              getTitlesWidget: (value, meta) {
                                if (value <= 0) {
                                  return Text(
                                    '0',
                                    style: theme.textTheme.labelSmall,
                                  );
                                }
                                if ((value - safeMax).abs() < 0.01) {
                                  return const SizedBox.shrink();
                                }
                                return Text(
                                  _compactMoney(value),
                                  style: theme.textTheme.labelSmall,
                                );
                              },
                            ),
                          ),
                          bottomTitles: AxisTitles(
                            sideTitles: SideTitles(
                              showTitles: true,
                              reservedSize: 28,
                              getTitlesWidget: (value, meta) {
                                final index = value.toInt();
                                if (index < 0 || index >= months.length) {
                                  return const SizedBox.shrink();
                                }
                                return Padding(
                                  padding: const EdgeInsets.only(top: 8),
                                  child: Text(
                                    _shortMonth(months[index]),
                                    style: theme.textTheme.labelSmall,
                                  ),
                                );
                              },
                            ),
                          ),
                        ),
                        gridData: FlGridData(
                          show: true,
                          drawVerticalLine: false,
                          horizontalInterval: safeMax / 3,
                          getDrawingHorizontalLine: (value) => FlLine(
                            color: colors.outlineVariant.withValues(alpha: 0.45),
                            strokeWidth: 1,
                          ),
                        ),
                        borderData: FlBorderData(show: false),
                        barGroups: [
                          for (var i = 0; i < months.length; i++)
                            BarChartGroupData(
                              x: i,
                              barsSpace: 4,
                              barRods: [
                                BarChartRodData(
                                  toY: monthly[months[i]]!.expense,
                                  width: 12,
                                  borderRadius: const BorderRadius.vertical(
                                    top: Radius.circular(8),
                                  ),
                                  color: expenseColor,
                                ),
                                BarChartRodData(
                                  toY: monthly[months[i]]!.income,
                                  width: 12,
                                  borderRadius: const BorderRadius.vertical(
                                    top: Radius.circular(8),
                                  ),
                                  color: incomeColor,
                                ),
                              ],
                            ),
                        ],
                      ),
                    ),
            ),
          ],
        ),
      ),
    );
  }

  static String _shortMonth(DateTime month) {
    const names = [
      'Jan',
      'Feb',
      'Mar',
      'Apr',
      'May',
      'Jun',
      'Jul',
      'Aug',
      'Sep',
      'Oct',
      'Nov',
      'Dec',
    ];
    return names[month.month - 1];
  }

  static String _compactMoney(double value) {
    if (value >= 1000) {
      final k = value / 1000;
      return k >= 10 ? '${k.round()}k' : '${k.toStringAsFixed(1)}k';
    }
    return value.round().toString();
  }
}

class _LegendDot extends StatelessWidget {
  const _LegendDot({required this.color, required this.label});

  final Color color;
  final String label;

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisSize: MainAxisSize.min,
      children: [
        Container(
          width: 8,
          height: 8,
          decoration: BoxDecoration(color: color, shape: BoxShape.circle),
        ),
        const SizedBox(width: 6),
        Text(label, style: Theme.of(context).textTheme.labelMedium),
      ],
    );
  }
}

class _SummaryCard extends StatelessWidget {
  const _SummaryCard({
    required this.icon,
    required this.iconBackground,
    required this.iconColor,
    required this.amount,
    required this.label,
  });

  final IconData icon;
  final Color iconBackground;
  final Color iconColor;
  final String amount;
  final String label;

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final colors = theme.colorScheme;

    return Card(
      color: colors.surface,
      elevation: 0,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(20),
        side: BorderSide(color: colors.outlineVariant.withValues(alpha: 0.5)),
      ),
      child: Padding(
        padding: const EdgeInsets.fromLTRB(12, 14, 12, 14),
        child: Row(
          children: [
            Container(
              width: 40,
              height: 40,
              decoration: BoxDecoration(
                color: iconBackground,
                borderRadius: BorderRadius.circular(12),
              ),
              child: Icon(icon, color: iconColor, size: 22),
            ),
            const SizedBox(width: 10),
            Expanded(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(
                    amount,
                    maxLines: 1,
                    overflow: TextOverflow.ellipsis,
                    style: theme.textTheme.titleMedium?.copyWith(
                      fontWeight: FontWeight.w700,
                    ),
                  ),
                  Text(label, style: theme.textTheme.labelMedium),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class _HistoryCard extends StatelessWidget {
  const _HistoryCard({
    required this.month,
    required this.income,
    required this.expense,
    required this.currency,
    required this.onTap,
  });

  final DateTime month;
  final double income;
  final double expense;
  final String currency;
  final VoidCallback onTap;

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final colors = theme.colorScheme;

    return Card(
      color: colors.surface,
      elevation: 0,
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(18),
        side: BorderSide(color: colors.outlineVariant.withValues(alpha: 0.5)),
      ),
      child: InkWell(
        borderRadius: BorderRadius.circular(18),
        onTap: onTap,
        child: Padding(
          padding: const EdgeInsets.fromLTRB(16, 14, 16, 14),
          child: Row(
            children: [
              Expanded(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Text('Month', style: theme.textTheme.labelMedium),
                    const SizedBox(height: 2),
                    Text(
                      formatMonthYear(month),
                      style: theme.textTheme.titleMedium?.copyWith(
                        fontWeight: FontWeight.w700,
                      ),
                    ),
                  ],
                ),
              ),
              Column(
                crossAxisAlignment: CrossAxisAlignment.end,
                children: [
                  Text(
                    formatMoney(income, currency),
                    style: theme.textTheme.titleSmall?.copyWith(
                      color: const Color(0xFF2F9E62),
                      fontWeight: FontWeight.w600,
                    ),
                  ),
                  const SizedBox(height: 2),
                  Text(
                    formatMoney(-expense, currency),
                    style: theme.textTheme.titleSmall?.copyWith(
                      color: colors.error,
                      fontWeight: FontWeight.w600,
                    ),
                  ),
                ],
              ),
            ],
          ),
        ),
      ),
    );
  }
}