dramaling-vocab-learning/backend/DramaLing.Api/Services/Review/ReviewService.cs

using DramaLing.Api.Models.DTOs;
using DramaLing.Api.Models.Entities;
using DramaLing.Api.Repositories;
using DramaLing.Api.Controllers;
using DramaLing.Api.Utils;

namespace DramaLing.Api.Services.Review;

public class ReviewService : IReviewService
{
    private readonly IFlashcardReviewRepository _reviewRepository;
    private readonly ILogger<ReviewService> _logger;

    public ReviewService(
        IFlashcardReviewRepository reviewRepository,
        ILogger<ReviewService> logger)
    {
        _reviewRepository = reviewRepository;
        _logger = logger;
    }

    public async Task<ApiResponse<object>> GetDueFlashcardsAsync(Guid userId, DueFlashcardsQuery query)
    {
        try
        {
            var dueFlashcards = await _reviewRepository.GetDueFlashcardsAsync(userId, query);
            var (todayDue, overdue, totalReviews) = await _reviewRepository.GetReviewStatsAsync(userId);

            // 轉換為符合前端期望的格式
            var flashcardData = dueFlashcards.Select(item => new
            {
                // 基本詞卡信息 (匹配 api_seeds.json 格式)
                id = item.Flashcard.Id.ToString(),
                word = item.Flashcard.Word,
                translation = item.Flashcard.Translation,
                definition = item.Flashcard.Definition ?? "",
                partOfSpeech = item.Flashcard.PartOfSpeech ?? "",
                pronunciation = item.Flashcard.Pronunciation ?? "",
                example = item.Flashcard.Example ?? "",
                exampleTranslation = item.Flashcard.ExampleTranslation ?? "",
                isFavorite = item.Flashcard.IsFavorite,
                difficultyLevelNumeric = item.Flashcard.DifficultyLevelNumeric,
                cefr = CEFRHelper.ToString(item.Flashcard.DifficultyLevelNumeric),
                createdAt = item.Flashcard.CreatedAt.ToString("yyyy-MM-ddTHH:mm:ssZ"),
                updatedAt = item.Flashcard.UpdatedAt.ToString("yyyy-MM-ddTHH:mm:ssZ"),

                // 圖片相關 (暫時設為預設值，因為需要額外查詢)
                hasExampleImage = false,
                primaryImageUrl = (string?)null,

                // 同義詞（暫時空陣列，未來可擴展）
                synonyms = new string[] { },

                // 複習相關信息 (新增)
                reviewInfo = item.Review != null ? new
                {
                    successCount = item.Review.SuccessCount,
                    nextReviewDate = item.Review.NextReviewDate.ToString("yyyy-MM-ddTHH:mm:ssZ"),
                    lastReviewDate = item.Review.LastReviewDate?.ToString("yyyy-MM-ddTHH:mm:ssZ"),
                    totalCorrectCount = item.Review.TotalCorrectCount,
                    totalWrongCount = item.Review.TotalWrongCount,
                    totalSkipCount = item.Review.TotalSkipCount,
                    isOverdue = item.Review.NextReviewDate < DateTime.UtcNow.Date,
                    daysSinceLastReview = item.Review.LastReviewDate.HasValue
                        ? (int)(DateTime.UtcNow - item.Review.LastReviewDate.Value).TotalDays
                        : 0
                } : new
                {
                    successCount = 0,
                    nextReviewDate = DateTime.UtcNow.AddDays(1).ToString("yyyy-MM-ddTHH:mm:ssZ"),
                    lastReviewDate = (string?)null,
                    totalCorrectCount = 0,
                    totalWrongCount = 0,
                    totalSkipCount = 0,
                    isOverdue = false,
                    daysSinceLastReview = 0
                }
            }).ToList();

            var response = new
            {
                flashcards = flashcardData,
                count = flashcardData.Count,
                metadata = new
                {
                    todayDue = todayDue,
                    overdue = overdue,
                    totalReviews = totalReviews,
                    studyStreak = 0 // 暫時設為0，未來可實作
                }
            };

            return new ApiResponse<object>
            {
                Success = true,
                Data = response,
                Message = null,
                Timestamp = DateTime.UtcNow
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error getting due flashcards for user {UserId}", userId);
            throw;
        }
    }

    public async Task<ApiResponse<ReviewResult>> SubmitReviewAsync(Guid userId, Guid flashcardId, ReviewRequest request)
    {
        try
        {
            // 獲取或創建複習記錄
            var review = await _reviewRepository.GetOrCreateReviewAsync(userId, flashcardId);

            // 處理複習結果
            var result = ProcessReview(review, request);

            // 更新記錄
            await _reviewRepository.UpdateReviewAsync(review);

            return new ApiResponse<ReviewResult>
            {
                Success = true,
                Data = result,
                Timestamp = DateTime.UtcNow
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error submitting review for flashcard {FlashcardId}", flashcardId);
            throw;
        }
    }

    public async Task<ApiResponse<ReviewStats>> GetReviewStatsAsync(Guid userId, string period = "today")
    {
        try
        {
            var (todayDue, overdue, totalReviews) = await _reviewRepository.GetReviewStatsAsync(userId);

            var stats = new ReviewStats
            {
                TodayReviewed = 0, // TODO: 實作當日複習統計
                TodayDue = todayDue,
                Overdue = overdue,
                TotalReviews = totalReviews,
                AverageAccuracy = 0.0, // TODO: 實作正確率統計
                StudyStreak = 0 // TODO: 實作連續學習天數
            };

            return new ApiResponse<ReviewStats>
            {
                Success = true,
                Data = stats,
                Timestamp = DateTime.UtcNow
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error getting review stats for user {UserId}", userId);
            throw;
        }
    }

    /// <summary>
    /// 處理複習結果的核心算法
    /// </summary>
    private ReviewResult ProcessReview(FlashcardReview review, ReviewRequest request)
    {
        if (request.WasSkipped)
        {
            // 跳過: 不改變成功次數，明天再複習
            review.TotalSkipCount++;
            review.NextReviewDate = DateTime.UtcNow.AddDays(1);
        }
        else
        {
            // 根據信心度判斷是否答對 (0=不熟悉答錯, 1-2=答對)
            var isCorrect = request.Confidence >= 1;

            if (isCorrect)
            {
                // 答對: 增加成功次數，計算新間隔
                review.SuccessCount++;
                review.TotalCorrectCount++;
                review.LastSuccessDate = DateTime.UtcNow;

                // 核心公式: 間隔 = 2^成功次數 天
                var intervalDays = (int)Math.Pow(2, review.SuccessCount);
                var maxInterval = 180; // 最大半年
                var finalInterval = Math.Min(intervalDays, maxInterval);

                review.NextReviewDate = DateTime.UtcNow.AddDays(finalInterval);
            }
            else
            {
                // 答錯: 重置成功次數，明天再複習
                review.SuccessCount = 0;
                review.TotalWrongCount++;
                review.NextReviewDate = DateTime.UtcNow.AddDays(1);
            }
        }

        review.LastReviewDate = DateTime.UtcNow;
        review.UpdatedAt = DateTime.UtcNow;

        return new ReviewResult
        {
            FlashcardId = review.FlashcardId,
            NewSuccessCount = review.SuccessCount,
            NextReviewDate = review.NextReviewDate,
            IntervalDays = (int)(review.NextReviewDate - DateTime.UtcNow).TotalDays,
            MasteryLevelChange = 0.0, // 暫時設為0
            IsNewRecord = review.CreatedAt == review.UpdatedAt
        };
    }
}