dramaling-vocab-learning/backend/DramaLing.Api/Services/Vocabulary/Options/OptionsVocabularyService.cs

using DramaLing.Api.Data;
using DramaLing.Api.Models.Configuration;
using DramaLing.Api.Models.Entities;
using DramaLing.Api.Services.Monitoring;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Options;
using System.Diagnostics;

namespace DramaLing.Api.Services;

/// <summary>
/// 選項詞彙庫服務實作
/// 提供基於 CEFR 等級、詞性和字數的智能選項生成
/// </summary>
public class OptionsVocabularyService : IOptionsVocabularyService
{
    private readonly DramaLingDbContext _context;
    private readonly IMemoryCache _cache;
    private readonly ILogger<OptionsVocabularyService> _logger;
    private readonly OptionsVocabularyOptions _options;
    private readonly OptionsVocabularyMetrics _metrics;

    public OptionsVocabularyService(
        DramaLingDbContext context,
        IMemoryCache cache,
        ILogger<OptionsVocabularyService> logger,
        IOptions<OptionsVocabularyOptions> options,
        OptionsVocabularyMetrics metrics)
    {
        _context = context;
        _cache = cache;
        _logger = logger;
        _options = options.Value;
        _metrics = metrics;
    }

    /// <summary>
    /// 生成智能干擾選項
    /// </summary>
    public async Task<List<string>> GenerateDistractorsAsync(
        string targetWord,
        string cefrLevel,
        string partOfSpeech,
        int count = 3)
    {
        var distractorsWithDetails = await GenerateDistractorsWithDetailsAsync(
            targetWord, cefrLevel, partOfSpeech, count);

        return distractorsWithDetails.Select(v => v.Word).ToList();
    }

    /// <summary>
    /// 生成智能干擾選項（含詳細資訊）
    /// </summary>
    public async Task<List<OptionsVocabulary>> GenerateDistractorsWithDetailsAsync(
        string targetWord,
        string cefrLevel,
        string partOfSpeech,
        int count = 3)
    {
        var stopwatch = Stopwatch.StartNew();

        try
        {
            // 記錄請求指標
            _metrics.RecordGenerationRequest(cefrLevel, partOfSpeech, count);

            _logger.LogInformation("Generating {Count} distractors for word '{Word}' (CEFR: {CEFR}, PartOfSpeech: {PartOfSpeech}) - Using fixed options",
                count, targetWord, cefrLevel, partOfSpeech);

            // 暫時使用固定選項，跳過複雜的詞彙篩選機制
            var fixedDistractors = new List<OptionsVocabulary>
            {
                new OptionsVocabulary
                {
                    Id = Guid.NewGuid(),
                    Word = "apple",
                    CEFRLevel = cefrLevel,
                    PartOfSpeech = partOfSpeech,
                    IsActive = true,
                    CreatedAt = DateTime.UtcNow,
                    UpdatedAt = DateTime.UtcNow
                },
                new OptionsVocabulary
                {
                    Id = Guid.NewGuid(),
                    Word = "orange",
                    CEFRLevel = cefrLevel,
                    PartOfSpeech = partOfSpeech,
                    IsActive = true,
                    CreatedAt = DateTime.UtcNow,
                    UpdatedAt = DateTime.UtcNow
                },
                new OptionsVocabulary
                {
                    Id = Guid.NewGuid(),
                    Word = "banana",
                    CEFRLevel = cefrLevel,
                    PartOfSpeech = partOfSpeech,
                    IsActive = true,
                    CreatedAt = DateTime.UtcNow,
                    UpdatedAt = DateTime.UtcNow
                }
            };

            // 計算字數長度
            foreach (var distractor in fixedDistractors)
            {
                distractor.CalculateWordLength();
            }

            // 排除目標詞彙本身（如果匹配）
            var selectedDistractors = fixedDistractors
                .Where(v => !string.Equals(v.Word, targetWord, StringComparison.OrdinalIgnoreCase))
                .Take(count)
                .ToList();

            _logger.LogInformation("Successfully generated {Count} fixed distractors for '{Word}': {Distractors}",
                selectedDistractors.Count, targetWord,
                string.Join(", ", selectedDistractors.Select(d => d.Word)));

            // 記錄生成完成指標
            stopwatch.Stop();
            _metrics.RecordGenerationDuration(stopwatch.Elapsed, selectedDistractors.Count);

            return selectedDistractors;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error generating distractors for word '{Word}'", targetWord);
            _metrics.RecordError("generation_failed", "GenerateDistractorsWithDetailsAsync");
            return new List<OptionsVocabulary>();
        }
    }

    /// <summary>
    /// 檢查詞彙庫是否有足夠的詞彙支援選項生成
    /// </summary>
    public async Task<bool> HasSufficientVocabularyAsync(string cefrLevel, string partOfSpeech)
    {
        try
        {
            var allowedLevels = GetAllowedCEFRLevels(cefrLevel);

            var count = await _context.OptionsVocabularies
                .Where(v => v.IsActive &&
                           allowedLevels.Contains(v.CEFRLevel) &&
                           v.PartOfSpeech == partOfSpeech)
                .CountAsync();

            var hasSufficient = count >= _options.MinimumVocabularyThreshold;

            _logger.LogDebug("Vocabulary count for CEFR: {CEFR}, PartOfSpeech: {PartOfSpeech}: {Count} (sufficient: {HasSufficient})",
                cefrLevel, partOfSpeech, count, hasSufficient);

            return hasSufficient;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error checking vocabulary sufficiency for CEFR: {CEFR}, PartOfSpeech: {PartOfSpeech}",
                cefrLevel, partOfSpeech);
            return false;
        }
    }

    /// <summary>
    /// 獲取允許的 CEFR 等級（包含相鄰等級）
    /// </summary>
    private static List<string> GetAllowedCEFRLevels(string targetLevel)
    {
        var levels = new[] { "A1", "A2", "B1", "B2", "C1", "C2" };
        var targetIndex = Array.IndexOf(levels, targetLevel);

        if (targetIndex == -1)
        {
            // 如果不是標準 CEFR 等級，只返回原等級
            return new List<string> { targetLevel };
        }

        var allowed = new List<string> { targetLevel };

        // 加入相鄰等級（允許難度稍有差異）
        if (targetIndex > 0)
            allowed.Add(levels[targetIndex - 1]);
        if (targetIndex < levels.Length - 1)
            allowed.Add(levels[targetIndex + 1]);

        return allowed;
    }
}