// src/Webshop.Application/Services/Customers/CheckoutService.cs
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Webshop.Application.DTOs.Customers;
using Webshop.Application.DTOs.Orders;
using Webshop.Application.Services.Customers.Interfaces;
using Webshop.Application.Services.Public.Interfaces;
using Webshop.Domain.Entities;
using Webshop.Domain.Enums;
using Webshop.Domain.Interfaces;
using Webshop.Infrastructure.Data;

namespace Webshop.Application.Services.Customers
{
    public class CheckoutService : ICheckoutService
    {
        private readonly ApplicationDbContext _context;
        private readonly IOrderRepository _orderRepository;
        private readonly ICustomerRepository _customerRepository;
        private readonly IShippingMethodRepository _shippingMethodRepository;
        private readonly ISettingService _settingService;
        private readonly IDiscountService _discountService;

        public CheckoutService(
            ApplicationDbContext context,
            IOrderRepository orderRepository,
            ICustomerRepository customerRepository,
            IShippingMethodRepository shippingMethodRepository,
            ISettingService settingService,
            IDiscountService discountService)
        {
            _context = context;
            _orderRepository = orderRepository;
            _customerRepository = customerRepository;
            _shippingMethodRepository = shippingMethodRepository;
            _settingService = settingService;
            _discountService = discountService;
        }

        public async Task<(bool Success, OrderDetailDto? CreatedOrder, string? ErrorMessage)> CreateOrderAsync(CreateOrderDto orderDto, string userId)
        {
            // Startet eine Datenbank-Transaktion. Entweder alles klappt, oder alles wird zurückgerollt.
            await using var transaction = await _context.Database.BeginTransactionAsync();

            try
            {
                // --- 1. Validierung der Eingabedaten ---
                var customer = await _customerRepository.GetByUserIdAsync(userId);
                if (customer == null) return (false, null, "Kundenprofil nicht gefunden.");

                var shippingMethod = await _shippingMethodRepository.GetByIdAsync(orderDto.ShippingMethodId);
                if (shippingMethod == null || !shippingMethod.IsActive) return (false, null, "Ungültige oder inaktive Versandmethode.");

                var paymentMethod = await _context.PaymentMethods.FindAsync(orderDto.PaymentMethodId);
                if (paymentMethod == null || !paymentMethod.IsActive) return (false, null, "Ungültige oder inaktive Zahlungsmethode.");

                if (!await _context.Addresses.AnyAsync(a => a.Id == orderDto.ShippingAddressId && a.CustomerId == customer.Id) ||
                    !await _context.Addresses.AnyAsync(a => a.Id == orderDto.BillingAddressId && a.CustomerId == customer.Id))
                {
                    return (false, null, "Ungültige oder nicht zugehörige Liefer- oder Rechnungsadresse.");
                }

                // --- 2. Artikel verarbeiten und Lagerbestand prüfen ---
                var orderItems = new List<OrderItem>();
                decimal itemsTotal = 0;

                foreach (var itemDto in orderDto.Items)
                {
                    var product = await _context.Products.FindAsync(itemDto.ProductId);
                    if (product == null || !product.IsActive)
                    {
                        await transaction.RollbackAsync();
                        return (false, null, $"Produkt mit ID {itemDto.ProductId} ist nicht verfügbar.");
                    }

                    if (product.StockQuantity < itemDto.Quantity)
                    {
                        await transaction.RollbackAsync();
                        return (false, null, $"Nicht genügend Lagerbestand für '{product.Name}'. Verfügbar: {product.StockQuantity}.");
                    }

                    // Lagerbestand reduzieren
                    product.StockQuantity -= itemDto.Quantity;

                    var orderItem = new OrderItem
                    {
                        ProductId = product.Id,
                        ProductVariantId = itemDto.ProductVariantId,
                        ProductName = product.Name,
                        ProductSKU = product.SKU,
                        Quantity = itemDto.Quantity,
                        UnitPrice = product.Price,
                        TotalPrice = product.Price * itemDto.Quantity
                    };

                    orderItems.Add(orderItem);
                    itemsTotal += orderItem.TotalPrice;
                }

                // --- 3. Preise, Rabatte, Steuern und Gesamtbetrag berechnen ---
                decimal discountAmount = await _discountService.CalculateDiscountAsync(orderItems, orderDto.CouponCode);
                decimal shippingCost = shippingMethod.BaseCost;
                decimal subTotal = itemsTotal + shippingCost - discountAmount;
                if (subTotal < 0) subTotal = 0;

                decimal taxRate = await _settingService.GetSettingValueAsync<decimal>("GlobalTaxRate", 0.19m);
                decimal taxAmount = subTotal * taxRate;
                decimal orderTotal = subTotal + taxAmount;

                // --- 4. Bestellung erstellen ---
                var newOrder = new Order
                {
                    CustomerId = customer.Id,
                    OrderNumber = $"WS-{DateTime.UtcNow:yyyyMMdd}-{new Random().Next(1000, 9999)}",
                    OrderDate = DateTimeOffset.UtcNow,
                    OrderStatus = OrderStatus.Pending.ToString(),
                    PaymentStatus = PaymentStatus.Pending.ToString(), // Wird später vom Zahlungsanbieter aktualisiert

                    OrderTotal = orderTotal,
                    ShippingCost = shippingCost,
                    TaxAmount = taxAmount,
                    DiscountAmount = discountAmount,

                    PaymentMethod = paymentMethod.Name,
                    PaymentMethodId = paymentMethod.Id,
                    ShippingMethodId = shippingMethod.Id,

                    BillingAddressId = orderDto.BillingAddressId,
                    ShippingAddressId = orderDto.ShippingAddressId,

                    OrderItems = orderItems
                };

                await _orderRepository.AddAsync(newOrder); // Speichert die Bestellung und die Artikel
                await _context.SaveChangesAsync(); // Speichert die Lagerbestandsänderungen

                await transaction.CommitAsync(); // Transaktion erfolgreich abschließen

                // --- 5. Erfolgreiche Antwort erstellen ---
                var createdOrder = await _orderRepository.GetByIdAsync(newOrder.Id); // Lade die erstellte Bestellung mit allen Details
                var orderDetailDto = MapToOrderDetailDto(createdOrder!); // Mapping zum DTO

                return (true, orderDetailDto, null);
            }
            catch (Exception ex)
            {
                await transaction.RollbackAsync();
                // Hier Fehler loggen
                return (false, null, $"Ein unerwarteter Fehler ist aufgetreten: {ex.Message}");
            }
        }

        // Helper-Methode für das Mapping, um Code-Duplizierung zu vermeiden
        private OrderDetailDto MapToOrderDetailDto(Order order)
        {
            return new OrderDetailDto
            {
                Id = order.Id,
                OrderNumber = order.OrderNumber,
                OrderDate = order.OrderDate,
                CustomerId = order.CustomerId,
                Status = Enum.Parse<OrderStatus>(order.OrderStatus),
                TotalAmount = order.OrderTotal,
                ShippingAddress = new AddressDto { /* Mapping */ },
                BillingAddress = new AddressDto { /* Mapping */ },
                PaymentMethod = order.PaymentMethod,
                PaymentStatus = Enum.Parse<PaymentStatus>(order.PaymentStatus),
                OrderItems = order.OrderItems.Select(oi => new OrderItemDto
                {
                    Id = oi.Id,
                    ProductId = oi.ProductId,
                    ProductVariantId = oi.ProductVariantId,
                    ProductName = oi.ProductName,
                    ProductSKU = oi.ProductSKU,
                    Quantity = oi.Quantity,
                    UnitPrice = oi.UnitPrice,
                    TotalPrice = oi.TotalPrice
                }).ToList()
            };
        }
    }
}