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

import '../models/fuel_entry.dart';
import '../models/vehicle.dart';
import '../services/app_state.dart';
import '../theme/app_theme.dart';
import '../widgets/hero_banner.dart';
import '../widgets/receipt_capture.dart';
import 'add_edit_vehicle_screen.dart';
import 'receipt_detail_screen.dart';

/// The three summary periods selectable below the hero totals — the
/// totals and the "Recent Activity" list below are both filtered to
/// whichever one is currently selected.
enum _DateRange {
  currentMonth('Current Month'),
  last3Months('Last 3 Months'),
  yearToDate('Year to Date');

  final String label;
  const _DateRange(this.label);

  /// Inclusive start of this range, relative to [now]. There's no
  /// explicit end — an entry just needs to not be *before* this to count,
  /// since receipts are never dated in the future in practice.
  DateTime startDate(DateTime now) {
    switch (this) {
      case _DateRange.currentMonth:
        return DateTime(now.year, now.month, 1);
      case _DateRange.last3Months:
        // Current month plus the two before it, from the 1st of the
        // earliest — DateTime normalizes a zero/negative month across a
        // year boundary correctly (e.g. month 0 becomes December prior year).
        return DateTime(now.year, now.month - 2, 1);
      case _DateRange.yearToDate:
        return DateTime(now.year, 1, 1);
    }
  }
}

/// The "Receipts" tab: every fuel entry across every vehicle, newest
/// first, styled after the theme mockups' receipt-focused layout — a
/// hero total, a date-range filter, then a flat, divided list of receipts
/// (date + amount + which vehicle) for that range, each tapping straight
/// through to that receipt's photo rather than to the vehicle it belongs to.
class ReceiptsScreen extends StatefulWidget {
  const ReceiptsScreen({super.key});

  @override
  State<ReceiptsScreen> createState() => _ReceiptsScreenState();
}

class _ReceiptsScreenState extends State<ReceiptsScreen> with AutomaticKeepAliveClientMixin {
  _DateRange _range = _DateRange.yearToDate;

  // Keeps this tab's state (the selected date range) alive when MainShell's
  // PageView builds/tears down tabs outside its cache extent as the user
  // swipes between them.
  @override
  bool get wantKeepAlive => true;

  Future<void> _addReceipt(BuildContext context) async {
    final vehicles = context.read<AppState>().vehicles;
    if (vehicles.isEmpty) {
      final newVehicleId = await Navigator.of(context).push<String>(
        MaterialPageRoute(
          builder: (_) => const AddEditVehicleScreen(promptToCreateForReceipt: true),
        ),
      );
      // Creating the vehicle was only ever a means to an end here — continue
      // straight into the receipt capture the user actually came here for,
      // rather than dropping them back on a Receipts tab that's still empty.
      if (newVehicleId != null && context.mounted) {
        await captureReceiptForVehicle(context, newVehicleId);
      }
      return;
    }
    if (vehicles.length == 1) {
      await captureReceiptForVehicle(context, vehicles.first.id);
      return;
    }

    final chosen = await showModalBottomSheet<Vehicle>(
      context: context,
      builder: (context) => SafeArea(
        child: ListView(
          shrinkWrap: true,
          children: [
            const Padding(
              padding: EdgeInsets.fromLTRB(16, 16, 16, 8),
              child: Text('Which vehicle is this receipt for?'),
            ),
            for (final vehicle in vehicles)
              ListTile(
                leading: const Icon(Icons.directions_car_outlined),
                title: Text(vehicle.displayLabel),
                onTap: () => Navigator.of(context).pop(vehicle),
              ),
          ],
        ),
      ),
    );
    if (chosen != null && context.mounted) {
      await captureReceiptForVehicle(context, chosen.id);
    }
  }

  void _openReceipt(BuildContext context, FuelEntry entry) {
    Navigator.of(context).push(
      MaterialPageRoute(builder: (_) => ReceiptDetailScreen(entryId: entry.id)),
    );
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);
    final appState = context.watch<AppState>();
    final rangeStart = _range.startDate(DateTime.now());
    final entries = appState.fuelEntries.where((e) => !e.date.isBefore(rangeStart)).toList()
      ..sort((a, b) => b.date.compareTo(a.date));
    final totalCost = entries.fold(0.0, (sum, e) => sum + e.totalCost);
    final totalGallons = entries.fold(0.0, (sum, e) => sum + e.gallons);
    final dateFormat = DateFormat.yMMMd();
    final currencyFormat = NumberFormat.simpleCurrency();
    final gallonsFormat = NumberFormat('#,##0.000');
    // The hero stat is a big headline number, not a precise figure — round
    // to whole gallons there rather than showing the same 3-decimal
    // precision the per-entry rows use.
    final heroGallonsFormat = NumberFormat('#,##0');

    return Scaffold(
      appBar: AppBar(
        title: const Text('Receipts'),
        actionsPadding: const EdgeInsets.only(right: 20),
        actions: [
          IconButton(
            icon: const Icon(Icons.add),
            tooltip: 'Log Fuel Receipt',
            onPressed: () => _addReceipt(context),
          ),
        ],
      ),
      body: ListView(
        padding: const EdgeInsets.fromLTRB(16, 8, 16, 16),
        children: [
          _HeroTotal(
            totalCost: totalCost,
            totalGallons: totalGallons,
            currencyFormat: currencyFormat,
            gallonsFormat: heroGallonsFormat,
            selectedRange: _range,
            onRangeSelected: (range) => setState(() => _range = range),
          ),
          Padding(
            padding: const EdgeInsets.fromLTRB(2, 14, 2, 8),
            child: Text(
              'Recent Activity',
              style: Theme.of(context).textTheme.titleSmall?.copyWith(fontWeight: FontWeight.w700),
            ),
          ),
          if (entries.isEmpty)
            const Padding(
              padding: EdgeInsets.symmetric(vertical: 24),
              child: Text('No fuel entries in this range.'),
            )
          else
            for (var i = 0; i < entries.length; i++) ...[
              if (i > 0) const Divider(height: 1),
              _ReceiptRow(
                entry: entries[i],
                vehicle: appState.vehicleById(entries[i].vehicleId),
                dateFormat: dateFormat,
                currencyFormat: currencyFormat,
                gallonsFormat: gallonsFormat,
                onTap: () => _openReceipt(context, entries[i]),
              ),
            ],
        ],
      ),
    );
  }
}

/// Sits inside the hero banner (on the gradient, not the plain scaffold
/// background), so selected/unselected use the hero's own white/translucent
/// text colors rather than the surface-based colorScheme ones.
class _DateRangeSelector extends StatelessWidget {
  final _DateRange selected;
  final ValueChanged<_DateRange> onSelected;

  const _DateRangeSelector({required this.selected, required this.onSelected});

  @override
  Widget build(BuildContext context) {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: [
        for (final range in _DateRange.values)
          GestureDetector(
            onTap: () => onSelected(range),
            behavior: HitTestBehavior.opaque,
            child: Padding(
              padding: const EdgeInsets.symmetric(vertical: 8),
              child: Text(
                range.label,
                style: TextStyle(
                  color: range == selected
                      ? AppTheme.heroText
                      : AppTheme.heroTextSecondary(context),
                  fontWeight: range == selected ? FontWeight.w800 : FontWeight.w600,
                  fontSize: 12.5,
                ),
              ),
            ),
          ),
      ],
    );
  }
}

class _HeroTotal extends StatelessWidget {
  final double totalCost;
  final double totalGallons;
  final NumberFormat currencyFormat;
  final NumberFormat gallonsFormat;
  final _DateRange selectedRange;
  final ValueChanged<_DateRange> onRangeSelected;

  const _HeroTotal({
    required this.totalCost,
    required this.totalGallons,
    required this.currencyFormat,
    required this.gallonsFormat,
    required this.selectedRange,
    required this.onRangeSelected,
  });

  @override
  Widget build(BuildContext context) {
    return HeroBanner(
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [
          HeroStatsRow(
            gallonsValue: gallonsFormat.format(totalGallons),
            costValue: currencyFormat.format(totalCost),
          ),
          const SizedBox(height: 7),
          _DateRangeSelector(selected: selectedRange, onSelected: onRangeSelected),
        ],
      ),
    );
  }
}

class _ReceiptRow extends StatelessWidget {
  final FuelEntry entry;
  final Vehicle? vehicle;
  final DateFormat dateFormat;
  final NumberFormat currencyFormat;
  final NumberFormat gallonsFormat;
  final VoidCallback onTap;

  const _ReceiptRow({
    required this.entry,
    required this.vehicle,
    required this.dateFormat,
    required this.currencyFormat,
    required this.gallonsFormat,
    required this.onTap,
  });

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

    return InkWell(
      onTap: onTap,
      child: Padding(
        padding: const EdgeInsets.symmetric(vertical: 10, horizontal: 2),
        child: Row(
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            Expanded(
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: [
                  Text(
                    dateFormat.format(entry.date),
                    style: const TextStyle(fontWeight: FontWeight.w700, fontSize: 15),
                  ),
                  const SizedBox(height: 3),
                  Text(
                    '${gallonsFormat.format(entry.gallons)} gal',
                    style: TextStyle(color: colorScheme.onSurfaceVariant, fontSize: 12.5),
                  ),
                ],
              ),
            ),
            Column(
              crossAxisAlignment: CrossAxisAlignment.end,
              children: [
                Text(
                  currencyFormat.format(entry.totalCost),
                  style: const TextStyle(fontWeight: FontWeight.w700, fontSize: 15),
                ),
                const SizedBox(height: 4),
                Container(
                  padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 3),
                  decoration: BoxDecoration(
                    color: colorScheme.primary.withValues(alpha: 0.10),
                    borderRadius: BorderRadius.circular(999),
                  ),
                  child: Text(
                    vehicle?.displayLabel ?? 'Unknown vehicle',
                    style: TextStyle(
                      color: colorScheme.primary,
                      fontSize: 10.5,
                      fontWeight: FontWeight.w700,
                    ),
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}