/// Overview: current balance, charts, and look-ahead balance forecast.
library;

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

import '../models/transaction_meta.dart';
import '../providers/bank_provider.dart';
import '../providers/tx_meta_provider.dart';
import '../utils/helpers.dart';
import '../utils/look_ahead.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';

enum _StatsMode { category, month }

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

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

class _OverviewScreenState extends State<OverviewScreen> {
  _StatsMode _mode = _StatsMode.category;
  var _lookAheadEnabled = false;
  DateTime _lookAheadMonth = monthStart(DateTime.now());

  void _goLookAheadMonth(int delta) {
    final next = addMonths(_lookAheadMonth, delta);
    final now = monthStart(DateTime.now());
    // Look ahead can go forward; still allow browsing past months.
    if (delta < 0 && next.isBefore(addMonths(now, -24))) return;
    if (delta > 0 && next.isAfter(addMonths(now, 36))) return;
    setState(() => _lookAheadMonth = next);
  }

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

    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, meta),
        ),
      ),
    );
  }

  Widget _buildBody(
    BuildContext context,
    BankController bank,
    TxMetaController meta,
  ) {
    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) {
      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 currentBalance = bank.balance?.amount ?? 0;
    final byCategory = meta.spendByCategory(bank.transactions);
    final byMonth = meta.spendByMonth(bank.transactions);
    final totalSpend = byCategory.values.fold<double>(0, (sum, v) => sum + v);

    final recurrings = recurringItemsFrom(
      transactions: bank.transactions,
      metaFor: meta.metaFor,
    );
    final today = dateOnly(DateTime.now());
    final lookAheadEnd = DateTime(
      _lookAheadMonth.year,
      _lookAheadMonth.month + 1,
      0,
    );
    final predicted = predictBalance(
      currentBalance: currentBalance,
      from: today,
      throughDate: lookAheadEnd,
      items: recurrings,
    );
    final projected = projectedOccurrences(
      items: recurrings,
      from: today,
      to: lookAheadEnd,
    );
    final nowMonth = monthStart(DateTime.now());

    return ListView(
      physics: const AlwaysScrollableScrollPhysics(),
      padding: const EdgeInsets.only(top: 8, bottom: 32),
      children: [
        Text('Current balance', style: theme.textTheme.labelMedium),
        const SizedBox(height: 4),
        Text(
          formatMoney(currentBalance, currency),
          style: theme.textTheme.headlineMedium,
        ),
        const SizedBox(height: 20),
        SwitchListTile(
          contentPadding: EdgeInsets.zero,
          secondary: const Icon(Icons.auto_graph_outlined),
          title: const Text('Look ahead'),
          subtitle: const Text(
            'Project balance from recurring income and spend',
          ),
          value: _lookAheadEnabled,
          onChanged: (value) {
            setState(() {
              _lookAheadEnabled = value;
              if (value && _lookAheadMonth.isBefore(nowMonth)) {
                _lookAheadMonth = nowMonth;
              }
            });
          },
        ),
        if (_lookAheadEnabled) ...[
          const SizedBox(height: 8),
          Card(
            child: Padding(
              padding: const EdgeInsets.fromLTRB(8, 8, 8, 16),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: [
                  Row(
                    children: [
                      IconButton(
                        tooltip: 'Previous month',
                        onPressed: () => _goLookAheadMonth(-1),
                        icon: const Icon(Icons.chevron_left),
                      ),
                      Expanded(
                        child: Text(
                          formatMonthYear(_lookAheadMonth),
                          textAlign: TextAlign.center,
                          style: theme.textTheme.titleMedium,
                        ),
                      ),
                      IconButton(
                        tooltip: 'Next month',
                        onPressed: () => _goLookAheadMonth(1),
                        icon: const Icon(Icons.chevron_right),
                      ),
                    ],
                  ),
                  Text(
                    'Predicted balance',
                    textAlign: TextAlign.center,
                    style: theme.textTheme.labelMedium,
                  ),
                  const SizedBox(height: 4),
                  Text(
                    formatMoney(predicted, currency),
                    textAlign: TextAlign.center,
                    style: theme.textTheme.headlineMedium?.copyWith(
                      color: predicted >= currentBalance
                          ? colors.primary
                          : colors.error,
                    ),
                  ),
                  const SizedBox(height: 4),
                  Text(
                    _lookAheadMonth == nowMonth && !lookAheadEnd.isAfter(today)
                        ? 'Mark transactions as recurring to forecast'
                        : 'Through ${formatDate(lookAheadEnd)} · '
                            '${projected.length} projected '
                            '${projected.length == 1 ? 'item' : 'items'}',
                    textAlign: TextAlign.center,
                    style: theme.textTheme.bodyMedium,
                  ),
                  if (recurrings.isEmpty) ...[
                    const SizedBox(height: 12),
                    Text(
                      'No recurring transactions yet. Open a transaction and '
                      'enable Recurring.',
                      textAlign: TextAlign.center,
                      style: theme.textTheme.bodyMedium,
                    ),
                  ] else if (projected.isNotEmpty) ...[
                    const SizedBox(height: 12),
                    for (final row in projected.take(12))
                      ListTile(
                        dense: true,
                        contentPadding: const EdgeInsets.symmetric(horizontal: 8),
                        leading: Icon(
                          row.item.category.icon,
                          color: row.item.category.color,
                        ),
                        title: Text(
                          row.item.description,
                          maxLines: 1,
                          overflow: TextOverflow.ellipsis,
                        ),
                        subtitle: Text(formatDate(row.date)),
                        trailing: Text(
                          formatMoney(row.item.amount, row.item.currency),
                          style: theme.textTheme.titleSmall?.copyWith(
                            color: row.item.amount >= 0
                                ? colors.primary
                                : colors.error,
                          ),
                        ),
                      ),
                    if (projected.length > 12)
                      Text(
                        '+${projected.length - 12} more…',
                        textAlign: TextAlign.center,
                        style: theme.textTheme.labelMedium,
                      ),
                  ],
                ],
              ),
            ),
          ),
        ],
        const SizedBox(height: 20),
        Text('Money out (categorized)', style: theme.textTheme.labelMedium),
        const SizedBox(height: 4),
        Text(
          formatMoney(totalSpend, currency),
          style: theme.textTheme.titleLarge,
        ),
        const SizedBox(height: 16),
        SegmentedButton<_StatsMode>(
          segments: const [
            ButtonSegment(
              value: _StatsMode.category,
              label: Text('Category'),
              icon: Icon(Icons.label_outline),
            ),
            ButtonSegment(
              value: _StatsMode.month,
              label: Text('By date'),
              icon: Icon(Icons.calendar_month_outlined),
            ),
          ],
          selected: {_mode},
          onSelectionChanged: (selection) {
            setState(() => _mode = selection.first);
          },
        ),
        const SizedBox(height: 20),
        SizedBox(
          height: 260,
          child: bank.transactions.isEmpty
              ? Center(
                  child: Text(
                    'Transactions will appear here once loaded.',
                    style: theme.textTheme.bodyMedium,
                  ),
                )
              : _mode == _StatsMode.category
                  ? _CategoryBars(data: byCategory, currency: currency)
                  : _MonthBars(data: byMonth, currency: currency),
        ),
        const SizedBox(height: 20),
        if (_mode == _StatsMode.category)
          ..._categoryLegend(context, byCategory, currency)
        else
          ..._monthLegend(context, byMonth, currency),
      ],
    );
  }

  List<Widget> _categoryLegend(
    BuildContext context,
    Map<TxCategory, double> data,
    String currency,
  ) {
    final entries = data.entries.toList()
      ..sort((a, b) => b.value.compareTo(a.value));
    if (entries.isEmpty) {
      return [
        Text(
          'No outflows yet. Categorize spending from the transaction list.',
          style: Theme.of(context).textTheme.bodyMedium,
        ),
      ];
    }
    return [
      for (final entry in entries)
        ListTile(
          contentPadding: EdgeInsets.zero,
          dense: true,
          leading: Icon(entry.key.icon, color: entry.key.color),
          title: Text(entry.key.label),
          trailing: Text(formatMoney(entry.value, currency)),
        ),
    ];
  }

  List<Widget> _monthLegend(
    BuildContext context,
    Map<String, double> data,
    String currency,
  ) {
    if (data.isEmpty) {
      return [
        Text(
          'No dated outflows to chart yet.',
          style: Theme.of(context).textTheme.bodyMedium,
        ),
      ];
    }
    return [
      for (final entry in data.entries.toList().reversed)
        ListTile(
          contentPadding: EdgeInsets.zero,
          dense: true,
          leading: const Icon(Icons.calendar_today_outlined),
          title: Text(entry.key),
          trailing: Text(formatMoney(entry.value, currency)),
        ),
    ];
  }
}

class _CategoryBars extends StatelessWidget {
  const _CategoryBars({required this.data, required this.currency});

  final Map<TxCategory, double> data;
  final String currency;

  @override
  Widget build(BuildContext context) {
    final entries = data.entries.toList()
      ..sort((a, b) => b.value.compareTo(a.value));
    if (entries.isEmpty) {
      return Center(
        child: Text(
          'Categorize transactions to see this chart',
          style: Theme.of(context).textTheme.bodyMedium,
          textAlign: TextAlign.center,
        ),
      );
    }

    final maxY = entries.map((e) => e.value).reduce((a, b) => a > b ? a : b);
    return BarChart(
      BarChartData(
        maxY: maxY * 1.15,
        barTouchData: BarTouchData(
          touchTooltipData: BarTouchTooltipData(
            getTooltipItem: (group, groupIndex, rod, rodIndex) {
              final entry = entries[group.x.toInt()];
              return BarTooltipItem(
                '${entry.key.label}\n${formatMoney(entry.value, currency)}',
                TextStyle(
                  color: Theme.of(context).colorScheme.onInverseSurface,
                ),
              );
            },
          ),
        ),
        titlesData: FlTitlesData(
          topTitles: const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          rightTitles:
              const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          leftTitles: const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          bottomTitles: AxisTitles(
            sideTitles: SideTitles(
              showTitles: true,
              reservedSize: 42,
              getTitlesWidget: (value, meta) {
                final index = value.toInt();
                if (index < 0 || index >= entries.length) {
                  return const SizedBox.shrink();
                }
                final label = entries[index].key.label;
                return Padding(
                  padding: const EdgeInsets.only(top: 8),
                  child: Text(
                    label.length > 8 ? '${label.substring(0, 7)}…' : label,
                    style: Theme.of(context).textTheme.labelSmall,
                  ),
                );
              },
            ),
          ),
        ),
        gridData: const FlGridData(show: false),
        borderData: FlBorderData(show: false),
        barGroups: [
          for (var i = 0; i < entries.length; i++)
            BarChartGroupData(
              x: i,
              barRods: [
                BarChartRodData(
                  toY: entries[i].value,
                  width: 18,
                  borderRadius:
                      const BorderRadius.vertical(top: Radius.circular(6)),
                  color: entries[i].key.color,
                ),
              ],
            ),
        ],
      ),
    );
  }
}

class _MonthBars extends StatelessWidget {
  const _MonthBars({required this.data, required this.currency});

  final Map<String, double> data;
  final String currency;

  @override
  Widget build(BuildContext context) {
    final entries = data.entries.toList();
    if (entries.isEmpty) {
      return Center(
        child: Text(
          'No monthly spend yet',
          style: Theme.of(context).textTheme.bodyMedium,
        ),
      );
    }

    final maxY = entries.map((e) => e.value).reduce((a, b) => a > b ? a : b);
    final colors = Theme.of(context).colorScheme;
    return BarChart(
      BarChartData(
        maxY: maxY * 1.15,
        barTouchData: BarTouchData(
          touchTooltipData: BarTouchTooltipData(
            getTooltipItem: (group, groupIndex, rod, rodIndex) {
              final entry = entries[group.x.toInt()];
              return BarTooltipItem(
                '${entry.key}\n${formatMoney(entry.value, currency)}',
                TextStyle(color: colors.onInverseSurface),
              );
            },
          ),
        ),
        titlesData: FlTitlesData(
          topTitles: const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          rightTitles:
              const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          leftTitles: const AxisTitles(sideTitles: SideTitles(showTitles: false)),
          bottomTitles: AxisTitles(
            sideTitles: SideTitles(
              showTitles: true,
              reservedSize: 28,
              getTitlesWidget: (value, meta) {
                final index = value.toInt();
                if (index < 0 || index >= entries.length) {
                  return const SizedBox.shrink();
                }
                final key = entries[index].key;
                final short = key.length >= 7 ? key.substring(5) : key;
                return Padding(
                  padding: const EdgeInsets.only(top: 8),
                  child: Text(
                    short,
                    style: Theme.of(context).textTheme.labelSmall,
                  ),
                );
              },
            ),
          ),
        ),
        gridData: const FlGridData(show: false),
        borderData: FlBorderData(show: false),
        barGroups: [
          for (var i = 0; i < entries.length; i++)
            BarChartGroupData(
              x: i,
              barRods: [
                BarChartRodData(
                  toY: entries[i].value,
                  width: 22,
                  borderRadius:
                      const BorderRadius.vertical(top: Radius.circular(6)),
                  color: colors.primary,
                ),
              ],
            ),
        ],
      ),
    );
  }
}