fin-tracker/app/lib/features/shell/app_shell.dart

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

class _Destination {
  const _Destination(this.path, this.icon, this.selectedIcon, this.label,
      {this.alsoMatches = const [], this.primary = false});
  final String path;
  final IconData icon;
  final IconData selectedIcon;
  final String label;

  /// Extra route prefixes that belong to this destination but do not start with [path] —
  /// `/instruments/pending` is reached from Импорт and must keep it highlighted, and the
  /// four phase-4 screens are reached from Аналитика the same way.
  final List<String> alsoMatches;

  /// Shown directly in the bottom bar on a phone. Everything else moves behind «Ещё».
  final bool primary;

  /// The longest prefix of [location] this destination claims, or -1 for no match.
  int matchLength(String location) {
    var best = -1;
    for (final p in [path, ...alsoMatches]) {
      final hit = p == '/' ? location == '/' : location.startsWith(p);
      if (hit && p.length > best) best = p.length;
    }
    return best;
  }
}

const _destinations = [
  _Destination('/', Icons.dashboard_outlined, Icons.dashboard, 'Обзор', primary: true),
  _Destination('/accounts', Icons.account_balance_outlined, Icons.account_balance, 'Счета',
      primary: true),
  _Destination('/portfolio', Icons.pie_chart_outline, Icons.pie_chart, 'Портфель',
      primary: true),
  // One entry for the four phase-4 screens. They keep their own top-level routes from the
  // contract and stay deep-linkable; the hub at `/analytics` is what the bottom bar and the
  // rail point at, and `alsoMatches` keeps it highlighted while you are inside any of them.
  _Destination('/analytics', Icons.insights_outlined, Icons.insights, 'Аналитика',
      alsoMatches: ['/income', '/rebalance', '/goals', '/tax'], primary: true),
  _Destination('/events', Icons.event_note_outlined, Icons.event_note, 'События'),
  _Destination('/imports', Icons.upload_file_outlined, Icons.upload_file, 'Импорт',
      alsoMatches: ['/instruments/pending']),
  _Destination('/cashflow', Icons.swap_horiz_outlined, Icons.swap_horiz, 'Потоки'),
  _Destination('/categories', Icons.category_outlined, Icons.category, 'Категории'),
  _Destination(
      '/transactions', Icons.receipt_long_outlined, Icons.receipt_long, 'Операции'),
  _Destination('/rules', Icons.rule_folder_outlined, Icons.rule_folder, 'Правила'),
  _Destination('/sync', Icons.sync_outlined, Icons.sync, 'Синк'),
  _Destination('/settings', Icons.settings_outlined, Icons.settings, 'Настройки'),
];

/// Breakpoints per the plan: bottom bar under 600, collapsed rail 600–1200,
/// extended rail at 1200 and above.
const _narrowBreakpoint = 600.0;
const _wideBreakpoint = 1200.0;

/// Adaptive navigation shell around the current route: a bottom
/// [NavigationBar] on narrow surfaces, a [NavigationRail] (collapsed or
/// extended) otherwise.
///
/// The rail shows every destination. The bottom bar shows the four primary ones plus
/// «Ещё», which opens the rest in a sheet: twelve destinations in a phone-width bar would
/// leave about 30 px per label, which is not navigation but decoration.
class AppShell extends StatelessWidget {
  const AppShell({required this.location, required this.child, super.key});

  final String location;
  final Widget child;

  int get _selectedIndex {
    // longest prefix wins, so /portfolio/instrument/311 keeps Портфель selected
    var best = -1;
    var bestLength = -1;
    for (var i = 0; i < _destinations.length; i++) {
      final length = _destinations[i].matchLength(location);
      if (length > bestLength) {
        best = i;
        bestLength = length;
      }
    }
    return best == -1 || bestLength < 0 ? 0 : best;
  }

  void _onSelect(BuildContext context, int index) {
    if (index != _selectedIndex) context.go(_destinations[index].path);
  }

  @override
  Widget build(BuildContext context) {
    final width = MediaQuery.sizeOf(context).width;

    if (width < _narrowBreakpoint) {
      final primary = _destinations.where((d) => d.primary).toList();
      final selected = _destinations[_selectedIndex];
      final primaryIndex = primary.indexOf(selected);

      return Scaffold(
        body: SafeArea(child: child),
        bottomNavigationBar: NavigationBar(
          // nothing primary matches ⇒ we are inside a screen that lives behind «Ещё»,
          // and «Ещё» is what should look active
          selectedIndex: primaryIndex >= 0 ? primaryIndex : primary.length,
          onDestinationSelected: (i) {
            if (i >= primary.length) {
              _showMore(context, selected);
            } else {
              final target = _destinations.indexOf(primary[i]);
              _onSelect(context, target);
            }
          },
          destinations: [
            for (final d in primary)
              NavigationDestination(
                icon: Icon(d.icon),
                selectedIcon: Icon(d.selectedIcon),
                label: d.label,
              ),
            NavigationDestination(
              icon: const Icon(Icons.more_horiz),
              selectedIcon: const Icon(Icons.more_horiz),
              label: primaryIndex >= 0 ? 'Ещё' : selected.label,
            ),
          ],
        ),
      );
    }

    final extended = width >= _wideBreakpoint;
    return Scaffold(
      body: Row(
        children: [
          NavigationRail(
            extended: extended,
            minExtendedWidth: 220,
            selectedIndex: _selectedIndex,
            onDestinationSelected: (i) => _onSelect(context, i),
            labelType: extended ? NavigationRailLabelType.none : NavigationRailLabelType.selected,
            destinations: [
              for (final d in _destinations)
                NavigationRailDestination(
                  icon: Icon(d.icon),
                  selectedIcon: Icon(d.selectedIcon),
                  label: Text(d.label),
                ),
            ],
          ),
          const VerticalDivider(width: 1),
          Expanded(child: SafeArea(child: child)),
        ],
      ),
    );
  }

  /// The non-primary destinations, as a sheet. The currently open one is ticked, so «Ещё»
  /// still answers "where am I".
  void _showMore(BuildContext context, _Destination current) {
    showModalBottomSheet<void>(
      context: context,
      showDragHandle: true,
      builder: (sheetContext) => SafeArea(
        child: ListView(
          shrinkWrap: true,
          children: [
            for (final d in _destinations.where((d) => !d.primary))
              ListTile(
                leading: Icon(d == current ? d.selectedIcon : d.icon),
                title: Text(d.label),
                selected: d == current,
                trailing: d == current ? const Icon(Icons.check) : null,
                onTap: () {
                  Navigator.of(sheetContext).pop();
                  if (d != current) context.go(d.path);
                },
              ),
          ],
        ),
      ),
    );
  }
}