// Version: 1.0.0
import 'package:flutter/material.dart';
import '../services/database_helper.dart';
import '../models/product.dart';

/// 請求作成画面（見積フローから連携）
class InvoiceScreen extends StatefulWidget {
  const InvoiceScreen({super.key});

  @override
  State<InvoiceScreen> createState() => _InvoiceScreenState();
}

class _InvoiceScreenState extends State<InvoiceScreen> {
  Customer? _selectedCustomer;
  final DatabaseHelper _db = DatabaseHelper.instance;
  List<Product> _products = [];
  List<Customer> _customers = [];
  List<LineItem> _items = [];
  String _estimateNumber = ''; // 見積番号（参考用）
  DateTime _invoiceDate = DateTime.now();

  @override
  void initState() {
    super.initState();
    _loadProducts();
    _loadCustomers();
  }

  Future<void> _loadProducts() async {
    try {
      final products = await _db.getProducts();
      setState(() => _products = products);
    } catch (e) {
      debugPrint('Product loading failed: $e');
    }
  }

  Future<void> _loadCustomers() async {
    try {
      final customers = await _db.getCustomers();
      setState(() => _customers = customers.where((c) => c.isDeleted == 0).toList());
    } catch (e) {
      debugPrint('Customer loading failed: $e');
    }
  }

  Future<void> _showCustomerPicker() async {
    if (_customers.isEmpty) await _loadCustomers();

    final selected = await showModalBottomSheet<Customer>(
      context: context,
      builder: (ctx) => SizedBox(
        height: MediaQuery.of(context).size.height * 0.4,
        child: ListView.builder(
          padding: const EdgeInsets.all(8),
          itemCount: _customers.length,
          itemBuilder: (ctx, index) => ListTile(
            title: Text(_customers[index].name),
            subtitle: Text('コード：${_customers[index].customerCode}'),
            onTap: () => Navigator.pop(ctx, _customers[index]),
          ),
        ),
      ),
    );

    if (selected is Customer && selected.id != _selectedCustomer?.id) {
      setState(() => _selectedCustomer = selected);
    }
  }

  void _addSelectedProducts() async {
    for (final product in _products) {
      final existingStock = product.stock;
      if (existingStock > 0 && !_items.any((i) => i.productId == product.id)) {
        setState(() => _items.add(LineItem(
          invoiceId: DateTime.now().millisecondsSinceEpoch,
          estimateNumber: 'EST${DateTime.now().year}${DateTime.now().month.toString().padLeft(2, '0')}',
          productId: product.id,
          productName: product.name,
          unitPrice: product.price,
          quantity: 1,
          total: product.price,
        )));
      }
    }
    _showAddDialog();
  }

  void _removeLineItem(int index) {
    setState(() => _items.removeAt(index));
  }

  String get _invoiceId => _items.isNotEmpty ? 'INV${_items.first.invoiceId.toString()}' : '';
  int get _totalAmount => _items.fold(0, (sum, item) => sum + item.total);
  int get _taxRate => _selectedCustomer?.taxRate ?? 8; // Default 10%
  int get _discountRate => _selectedCustomer?.discountRate ?? 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('請求作成')),
      body: ListView(
        padding: const EdgeInsets.all(16),
        children: [
          _buildCustomerField(),
          const SizedBox(height: 16),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              const Text('請求日'),
              InkWell(
                onTap: () => _selectDate(),
                child: Text('${_invoiceDate.year}-${_invoiceDate.month.toString().padLeft(2, '0')}-${_invoiceDate.day.toString().padLeft(2, '0')}'),
              ),
            ],
          ),
          const SizedBox(height: 8),
          Card(
            margin: EdgeInsets.zero,
            child: ExpansionTile(
              title: const Text('請求商品'),
              children: [
                if (_items.isEmpty) ...[
                  Padding(
                    padding: const EdgeInsets.all(16),
                    child: Column(
                      children: [
                        Icon(Icons.receipt_long_outlined, size: 48, color: Colors.grey.shade400),
                        const SizedBox(height: 8),
                        Text('商品を追加してください', style: TextStyle(color: Colors.grey.shade600)),
                      ],
                    ),
                  ),
                ] else ...[
                  ListView.builder(
                    shrinkWrap: true,
                    padding: EdgeInsets.zero,
                    itemCount: _items.length,
                    itemBuilder: (context, index) => Card(
                      margin: const EdgeInsets.symmetric(vertical: 4),
                      child: ListTile(
                        leading: CircleAvatar(
                          backgroundColor: Colors.purple.shade100,
                          child: Icon(Icons.receipt_long, color: Colors.purple),
                        ),
                        title: Text(_items[index].productName),
                        subtitle: Column(
                          crossAxisAlignment: CrossAxisAlignment.start,
                          children: [
                            Text('単価：¥${_items[index].unitPrice}'),
                            Text('数量：${_items[index].quantity} pcs'),
                          ],
                        ),
                        trailing: IconButton(icon: const Icon(Icons.delete, color: Colors.red), onPressed: () => _removeLineItem(index)),
                      ),
                    ),
                  ),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }

  Widget _buildCustomerField() {
    return TextField(
      decoration: InputDecoration(
        labelText: '得意先',
        hintText: _selectedCustomer != null ? _selectedCustomer.name : '得意先マスタから選択',
        prefixIcon: Icon(Icons.person_search),
        isReadOnly: true,
      ),
      onTap: () => _showCustomerPicker(),
    );
  }

  void _selectDate() async {
    final picked = await showDatePicker(
      context: context,
      initialDate: _invoiceDate,
      firstDate: DateTime(2026),
      lastDate: DateTime(2100),
    );

    if (picked != null) setState(() => _invoiceDate = picked);
  }

  void _showAddDialog() async {
    final selected = await showModalBottomSheet<Product>(
      context: context,
      builder: (ctx) => ListView.builder(
        padding: EdgeInsets.zero,
        itemCount: _products.length,
        itemBuilder: (ctx, index) => CheckboxListTile(
          title: Text(_products[index].name),
          subtitle: Text('¥${_products[index].price} / 在庫：${_products[index].stock}${_products[index].unit ?? ''}'),
          value: _items.any((i) => i.productId == _products[index].id),
          onChanged: (value) {
            if (value && _products[index].stock > 0) _addSelectedProducts();
          },
        ),
      ),
    );

    if (selected != null && selected.id != null && _products[selected.id]?.stock! > 0 && !_items.any((i) => i.productId == selected.id)) {
      setState(() => _items.add(LineItem(
        invoiceId: _invoiceId,
        estimateNumber: 'EST${DateTime.now().year}${DateTime.now().month.toString().padLeft(2, '0')}',
        productId: selected.id,
        productName: selected.name,
        unitPrice: selected.price,
        quantity: 1,
        total: selected.price,
      )));
    }
  }

  void _showSaveDialog() async {
    if (_items.isEmpty) {
      ScaffoldMessenger.of(context).showSnackBar(
        const SnackBar(content: Text('商品を追加してください')),
      );
      return;
    }

    showDialog(
      context: context,
      builder: (ctx) => AlertDialog(
        title: const Text('請求書発行'),
        content: SingleChildScrollView(
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              if (_selectedCustomer != null) ...[
                Padding(
                  padding: const EdgeInsets.symmetric(vertical: 8),
                  child: Text('得意先：${_selectedCustomer!.name}'),
                ),
              ],
              Text('請求 ID: ${_items.isNotEmpty ? _invoiceId : ''}'),
              Text('見積番号：${_estimateNumber.isEmpty ? '（新規作成）' : _estimateNumber}'),
              Text('請求日：${_invoiceDate.toLocal()}'),
              Text('税率：${_taxRate}% / 割引率：${_discountRate}%'),
              const SizedBox(height: 8),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  const Text('合計金額（税込）', style: TextStyle(fontWeight: FontWeight.bold)),
                  Text('¥${_totalAmount}'),
                ],
              ),
              if (_items.isNotEmpty) ...[
                Divider(),
                ..._items.map((item) => Padding(
                  padding: const EdgeInsets.symmetric(vertical: 4),
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: [
                      Text(item.productName),
                      Text('¥${item.unitPrice} × ${item.quantity} = ¥${item.total}'),
                    ],
                  ),
                )),
              ],
            ],
          ),
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(ctx),
            child: const Text('キャンセル'),
          ),
          ElevatedButton(
            onPressed: () async {
              if (_estimateNumber.isEmpty) {
                _estimateNumber = 'EST${DateTime.now().year}${DateTime.now().month.toString().padLeft(2, '0')}';
              }

              Navigator.pop(ctx);
              ScaffoldMessenger.of(context).showSnackBar(
                const SnackBar(content: Text('請求書発行しました'))..behavior: SnackBarBehavior.floating,
              );
            },
            style: ElevatedButton.styleFrom(backgroundColor: Colors.blue),
            child: const Text('発行'),
          ),
        ],
      ),
    );
  }

  void _saveInvoice() async {
    if (_items.isEmpty) return;
    // TODO: DB に請求書データを保存
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text('請求書 ${_invoiceId} をデータベースに保存')),
    );
  }

  String _formatAmount(int amount) {
    const symbol = '¥';
    final integerPart = amount ~/ 100; // 円部分
    final centPart = amount % 100;     // 銭部分

    return '$symbol${integerPart.toString().padLeft(2, '0')}.${centPart.toString().padLeft(2, '0')}';
  }
}

/// 請求行モデル（見積番号参照）
class LineItem {
  final String? invoiceId;
  final String estimateNumber; // 見積番号（関連付け用）
  final int? productId;
  final String productName;
  final int unitPrice;
  int quantity = 1;
  int get total => quantity * unitPrice;

  LineItem({this.invoiceId, this.estimateNumber = '', this.productId, required this.productName, required this.unitPrice, this.quantity = 1});
}