ShopSolution-backend/Webshop.Application/Services/Admin/AdminDiscountService.cs

// src/Webshop.Application/Services/Admin/AdminDiscountService.cs
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Webshop.Application;
using Webshop.Application.DTOs.Discounts;
using Webshop.Application.Services.Admin.Interfaces;
using Webshop.Domain.Entities;
using Webshop.Domain.Enums;
using Webshop.Domain.Interfaces;

namespace Webshop.Application.Services.Admin
{
    public class AdminDiscountService : IAdminDiscountService
    {
        private readonly IDiscountRepository _discountRepository;

        public AdminDiscountService(IDiscountRepository discountRepository)
        {
            _discountRepository = discountRepository;
        }

        public async Task<ServiceResult<IEnumerable<DiscountDto>>> GetAllDiscountsAsync()
        {
            var discounts = await _discountRepository.GetAllAsync();
            var dtos = discounts.Select(MapToDto).ToList();
            return ServiceResult.Ok<IEnumerable<DiscountDto>>(dtos);
        }

        public async Task<ServiceResult<DiscountDto>> GetDiscountByIdAsync(Guid id)
        {
            var discount = await _discountRepository.GetByIdAsync(id);
            if (discount == null)
            {
                return ServiceResult.Fail<DiscountDto>(ServiceResultType.NotFound, $"Rabatt mit ID '{id}' nicht gefunden.");
            }
            return ServiceResult.Ok(MapToDto(discount));
        }

        public async Task<ServiceResult<DiscountDto>> CreateDiscountAsync(DiscountDto discountDto)
        {
            if (discountDto.RequiresCouponCode && !string.IsNullOrEmpty(discountDto.CouponCode))
            {
                var existing = await _discountRepository.GetByCouponCodeAsync(discountDto.CouponCode);
                if (existing != null)
                {
                    return ServiceResult.Fail<DiscountDto>(ServiceResultType.Conflict, $"Der Gutscheincode '{discountDto.CouponCode}' existiert bereits.");
                }
            }

            var discount = MapToEntity(discountDto);
            discount.Id = Guid.NewGuid();

            await _discountRepository.AddAsync(discount);
            return ServiceResult.Ok(MapToDto(discount));
        }

        public async Task<ServiceResult> UpdateDiscountAsync(DiscountDto discountDto)
        {
            var existingDiscount = await _discountRepository.GetByIdAsync(discountDto.Id);
            if (existingDiscount == null)
            {
                return ServiceResult.Fail(ServiceResultType.NotFound, $"Rabatt mit ID '{discountDto.Id}' nicht gefunden.");
            }

            if (discountDto.RequiresCouponCode && !string.IsNullOrEmpty(discountDto.CouponCode))
            {
                var existing = await _discountRepository.GetByCouponCodeAsync(discountDto.CouponCode);
                if (existing != null && existing.Id != discountDto.Id)
                {
                    return ServiceResult.Fail(ServiceResultType.Conflict, $"Der Gutscheincode '{discountDto.CouponCode}' wird bereits von einem anderen Rabatt verwendet.");
                }
            }

            // Update simple properties
            existingDiscount.Name = discountDto.Name;
            existingDiscount.Description = discountDto.Description;
            existingDiscount.DiscountType = discountDto.DiscountType.ToString();
            existingDiscount.DiscountValue = discountDto.DiscountValue;
            existingDiscount.StartDate = discountDto.StartDate;
            existingDiscount.EndDate = discountDto.EndDate;
            existingDiscount.IsActive = discountDto.IsActive;
            existingDiscount.RequiresCouponCode = discountDto.RequiresCouponCode;
            existingDiscount.CouponCode = discountDto.RequiresCouponCode ? discountDto.CouponCode : null;
            existingDiscount.MinimumOrderAmount = discountDto.MinimumOrderAmount;
            existingDiscount.MaximumUsageCount = discountDto.MaximumUsageCount;

            // Sync assigned products
            existingDiscount.ProductDiscounts.Clear();
            if (discountDto.AssignedProductIds != null)
            {
                foreach (var productId in discountDto.AssignedProductIds)
                {
                    existingDiscount.ProductDiscounts.Add(new ProductDiscount { DiscountId = existingDiscount.Id, ProductId = productId });
                }
            }

            // Sync assigned categories
            existingDiscount.categorieDiscounts.Clear();
            if (discountDto.AssignedCategoryIds != null)
            {
                foreach (var categoryId in discountDto.AssignedCategoryIds)
                {
                    existingDiscount.categorieDiscounts.Add(new CategorieDiscount { DiscountId = existingDiscount.Id, categorieId = categoryId });
                }
            }

            await _discountRepository.UpdateAsync(existingDiscount);
            return ServiceResult.Ok();
        }

        public async Task<ServiceResult> DeleteDiscountAsync(Guid id)
        {
            var discount = await _discountRepository.GetByIdAsync(id);
            if (discount == null)
            {
                return ServiceResult.Fail(ServiceResultType.NotFound, $"Rabatt mit ID '{id}' nicht gefunden.");
            }

            await _discountRepository.DeleteAsync(id);
            return ServiceResult.Ok();
        }


        // Helper methods for mapping
        private DiscountDto MapToDto(Discount discount)
        {
            return new DiscountDto
            {
                Id = discount.Id,
                Name = discount.Name,
                Description = discount.Description,
                DiscountType = Enum.Parse<DiscountType>(discount.DiscountType),
                DiscountValue = discount.DiscountValue,
                StartDate = discount.StartDate,
                EndDate = discount.EndDate,
                IsActive = discount.IsActive,
                RequiresCouponCode = discount.RequiresCouponCode,
                CouponCode = discount.CouponCode,
                MinimumOrderAmount = discount.MinimumOrderAmount,
                MaximumUsageCount = discount.MaximumUsageCount,
                CurrentUsageCount = discount.CurrentUsageCount,
                AssignedProductIds = discount.ProductDiscounts.Select(pd => pd.ProductId).ToList(),
                AssignedCategoryIds = discount.categorieDiscounts.Select(cd => cd.categorieId).ToList()
            };
        }

        private Discount MapToEntity(DiscountDto dto)
        {
            return new Discount
            {
                Id = dto.Id,
                Name = dto.Name,
                Description = dto.Description,
                DiscountType = dto.DiscountType.ToString(),
                DiscountValue = dto.DiscountValue,
                StartDate = dto.StartDate,
                EndDate = dto.EndDate,
                IsActive = dto.IsActive,
                RequiresCouponCode = dto.RequiresCouponCode,
                CouponCode = dto.RequiresCouponCode ? dto.CouponCode : null,
                MinimumOrderAmount = dto.MinimumOrderAmount,
                MaximumUsageCount = dto.MaximumUsageCount,
                CurrentUsageCount = dto.CurrentUsageCount,
                ProductDiscounts = dto.AssignedProductIds.Select(pid => new ProductDiscount { ProductId = pid }).ToList(),
                categorieDiscounts = dto.AssignedCategoryIds.Select(cid => new CategorieDiscount { categorieId = cid }).ToList()
            };
        }
    }
}