TechHelper/TechHelper.Server/Services/QuestionService.cs

using AutoMapper;
using Entities.Contracts;
using SharedDATA.Api;
using TechHelper.Services;
using System.Linq.Expressions;
using System.Linq;
using Entities; // 引入你的 Question 实体所在的命名空间
using Microsoft.EntityFrameworkCore;
using Entities.DTO; // 引入 EF Core 用于 Include (如果需要)

namespace TechHelper.Server.Services
{
	public class QuestionService : IQuestionService
	{
		private readonly IUnitOfWork _work;
		// 如果不再需要 AutoMapper 进行实体到 DTO 的映射，可以移除 _mapper 字段
		// 但如果 AutoMapper 在其他服务中用于其他映射，或者将来可能需要，可以保留
		private readonly IMapper _mapper;
		private readonly IExamService _examService;

		public QuestionService(IUnitOfWork work, IMapper mapper, IExamService examService)
		{
			_work = work;
			_mapper = mapper;
			_examService = examService;
		}

		public async Task<ApiResponse> AddAsync(Question model)
		{
			try
			{
				// 可以在此处进行业务逻辑校验，例如检查题目是否已存在
				var existingQuestion = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(
					predicate: q => q.Title == model.Title && !q.IsDeleted
				);

				if (existingQuestion != null)
				{
					return ApiResponse.Error($"题目 '{model.Title}' 已存在，请勿重复添加。");
				}

				// 设置创建时间、创建者等通用属性
				model.Id = Guid.NewGuid();
				model.CreatedAt = DateTime.UtcNow;
				model.UpdatedAt = DateTime.UtcNow;
				model.IsDeleted = false;


				await _work.GetRepository<Question>().InsertAsync(model);
				await _work.SaveChangesAsync();

				// 直接返回 Question 实体
				return ApiResponse.Success("题目添加成功。", model);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"添加题目失败: {ex.Message}");
			}
		}

		public async Task<ApiResponse> DeleteAsync(Guid id)
		{
			try
			{
				var questionToDelete = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(predicate: q => q.Id == id && !q.IsDeleted);

				if (questionToDelete == null)
				{
					return ApiResponse.Error($"找不到 ID 为 {id} 的题目，或者该题目已被删除。");
				}

				// 软删除
				questionToDelete.IsDeleted = true;
				questionToDelete.UpdatedAt = DateTime.UtcNow;
				_work.GetRepository<Question>().Update(questionToDelete);

				await _work.SaveChangesAsync();

				return ApiResponse.Success($"ID 为 {id} 的题目已成功删除 (软删除)。");
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"删除题目时发生错误: {ex.Message}");
			}
		}

		public async Task<ApiResponse> FindByTitle(string title)
		{
			try
			{
				var question = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(
					predicate: q => q.Title == title && !q.IsDeleted
				);

				if (question == null)
				{
					return ApiResponse.Error($"未找到题目 '{title}'。");
				}

				// 直接返回 Question 实体
				return ApiResponse.Success(result: question);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"查找题目时出现问题: {ex.Message}");
			}
		}

		public async Task<ApiResponse> CheckTitlesExistence(IEnumerable<string> titles)
		{
			try
			{
				if (titles == null || !titles.Any())
				{
					return ApiResponse.Success("未指定查询的题目文本，返回空结果。", new Dictionary<string, bool>());
				}

				var distinctTitles = titles.Distinct(StringComparer.OrdinalIgnoreCase).ToList();

				var existingQuestions = await _work.GetRepository<Question>().GetAllAsync(
					predicate: q => distinctTitles.Contains(q.Title) && !q.IsDeleted
				);

				var existingQuestionTexts = new HashSet<string>(existingQuestions.Select(q => q.Title), StringComparer.OrdinalIgnoreCase);

				var resultDictionary = new Dictionary<string, bool>(StringComparer.OrdinalIgnoreCase);
				foreach (var title in titles)
				{
					resultDictionary[title] = existingQuestionTexts.Contains(title);
				}

				return ApiResponse.Success(result: resultDictionary);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"批量查找题目存在性时出现问题: {ex.Message}");
			}
		}

		public async Task<ApiResponse> GetAllAsync(QueryParameter query)
		{
			try
			{
				Expression<Func<Question, bool>> predicate = q => !q.IsDeleted;

				if (!string.IsNullOrWhiteSpace(query.Search))
				{
					predicate = predicate.And(q => q.Title.Contains(query.Search));
				}

				Func<IQueryable<Question>, IOrderedQueryable<Question>> orderBy = null;
				if (true)
				{

					orderBy = q => q.OrderByDescending(x => x.CreatedAt);
				}
				else
				{
					orderBy = q => q.OrderByDescending(x => x.CreatedAt);
				}

				var questions = await _work.GetRepository<Question>().GetPagedListAsync(
					predicate: predicate,
					orderBy: orderBy,
					pageIndex: query.PageIndex,
					pageSize: query.PageSize
				);

				if (!questions.Items.Any())
				{
					return ApiResponse.Error("未找到任何题目。", Enumerable.Empty<Question>()); // 返回空 Question 集合
				}

				// 直接返回 Question 实体集合
				return ApiResponse.Success(result: questions);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"获取题目列表时出现问题: {ex.Message}");
			}
		}

		public async Task<ApiResponse> GetAsync(Guid id)
		{
			try
			{
				var question = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(predicate: q => q.Id == id && !q.IsDeleted);

				if (question == null)
				{
					return ApiResponse.Error($"找不到 ID 为 {id} 的题目。");
				}

				// 直接返回 Question 实体
				return ApiResponse.Success(result: question);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"获取题目时发生错误: {ex.Message}");
			}
		}

		public async Task<ApiResponse> UpdateAsync(Question model)
		{
			try
			{
				var existingQuestion = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(predicate: q => q.Id == model.Id && !q.IsDeleted);

				if (existingQuestion == null)
				{
					return ApiResponse.Error($"找不到 ID 为 {model.Id} 的题目，无法更新。");
				}

				// 检查更新后的题目文本是否与现有其他题目重复
				var duplicateCheck = await _work.GetRepository<Question>().GetFirstOrDefaultAsync(
					predicate: q => q.Id != model.Id && q.Title == model.Title && !q.IsDeleted
				);

				if (duplicateCheck != null)
				{
					return ApiResponse.Error($"题目文本 '{model.Title}' 已被其他题目占用，请修改。");
				}

				// 手动复制属性或使用 AutoMapper (如果保留了 _mapper 字段)
				// 如果选择手动复制，请确保复制所有需要更新的属性
				existingQuestion = model;

				_work.GetRepository<Question>().Update(existingQuestion);
				await _work.SaveChangesAsync();

				// 直接返回更新后的 Question 实体
				return ApiResponse.Success("题目更新成功。", existingQuestion);
			}
			catch (Exception ex)
			{
				return ApiResponse.Error($"更新题目失败: {ex.Message}");
			}
		}

	}

	// PredicateBuilder 保持不变，如果你没有使用 LinqKit，这部分是必需的
	public static class PredicateBuilder
	{
		public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
		{
			var invokedExpr = Expression.Invoke(second, first.Parameters.Cast<Expression>());
			return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(first.Body, invokedExpr), first.Parameters);
		}

		public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
		{
			var invokedExpr = Expression.Invoke(second, first.Parameters.Cast<Expression>());
			return Expression.Lambda<Func<T, bool>>(Expression.OrElse(first.Body, invokedExpr), first.Parameters);
		}

		public static Expression<Func<T, bool>> True<T>() { return f => true; }
		public static Expression<Func<T, bool>> False<T>() { return f => false; }
	}
}