refactor: 清理未使用的後端服務並建立審計報告

- 移除4個未使用的服務檔案：
  • IGeminiAnalyzer.cs - 未實作的介面
  • AudioCacheService.cs - 未使用的音頻快取服務
  • AzureSpeechService.cs - 未使用的語音服務
  • UsageTrackingService.cs - 未使用的使用量追蹤服務

- 移除相關的 DI 容器註冊
- 移除空的 Services/Media/Audio/ 目錄
- 新增完整的後端服務審計報告文件
- 保留核心功能服務的所有依賴關係

編譯測試通過，功能完整保留，程式碼減少約500+行

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/DramaLing.Api/Extensions/ServiceCollectionExtensions.cs

@@ -136,9 +136,6 @@ public static class ServiceCollectionExtensions
     public static IServiceCollection AddBusinessServices(this IServiceCollection services)
     {
         services.AddScoped<IAuthService, AuthService>();
-        services.AddScoped<IUsageTrackingService, UsageTrackingService>();
-        services.AddScoped<IAzureSpeechService, AzureSpeechService>();
-        services.AddScoped<IAudioCacheService, AudioCacheService>();
 
         // 媒體服務
         services.AddScoped<IImageProcessingService, ImageProcessingService>();

backend/DramaLing.Api/Services/AI/Analysis/IGeminiAnalyzer.cs

@@ -1,8 +0,0 @@
-using DramaLing.Api.Models.DTOs;
-
-namespace DramaLing.Api.Services.AI.Analysis;
-
-public interface IGeminiAnalyzer
-{
-    Task<SentenceAnalysisData> AnalyzeSentenceAsync(string inputText, AnalysisOptions options);
-}

backend/DramaLing.Api/Services/Infrastructure/Monitoring/UsageTrackingService.cs

@@ -1,255 +0,0 @@
-using Microsoft.EntityFrameworkCore;
-using DramaLing.Api.Data;
-using DramaLing.Api.Models.Entities;
-
-namespace DramaLing.Api.Services;
-
-public interface IUsageTrackingService
-{
-    Task<bool> CheckUsageLimitAsync(Guid userId, bool isPremium = false);
-    Task RecordSentenceAnalysisAsync(Guid userId);
-    Task RecordWordQueryAsync(Guid userId, bool wasHighValue);
-    Task<UserUsageStats> GetUsageStatsAsync(Guid userId);
-}
-
-public class UsageTrackingService : IUsageTrackingService
-{
-    private readonly DramaLingDbContext _context;
-    private readonly ILogger<UsageTrackingService> _logger;
-
-    // 免費用戶限制
-    private const int FREE_USER_ANALYSIS_LIMIT = 5;
-    private const int FREE_USER_RESET_HOURS = 3;
-
-    public UsageTrackingService(DramaLingDbContext context, ILogger<UsageTrackingService> logger)
-    {
-        _context = context;
-        _logger = logger;
-    }
-
-    /// <summary>
-    /// 檢查用戶使用限制
-    /// </summary>
-    public async Task<bool> CheckUsageLimitAsync(Guid userId, bool isPremium = false)
-    {
-        try
-        {
-            if (isPremium)
-            {
-                return true; // 付費用戶無限制
-            }
-
-            var resetTime = DateTime.UtcNow.AddHours(-FREE_USER_RESET_HOURS);
-            var recentUsage = await _context.WordQueryUsageStats
-                .Where(stats => stats.UserId == userId && stats.CreatedAt >= resetTime)
-                .SumAsync(stats => stats.SentenceAnalysisCount + stats.LowValueWordClicks);
-
-            var canUse = recentUsage < FREE_USER_ANALYSIS_LIMIT;
-
-            _logger.LogInformation("Usage check for user {UserId}: {RecentUsage}/{Limit}, Can use: {CanUse}",
-                userId, recentUsage, FREE_USER_ANALYSIS_LIMIT, canUse);
-
-            return canUse;
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error checking usage limit for user {UserId}", userId);
-            return false; // 出錯時拒絕使用
-        }
-    }
-
-    /// <summary>
-    /// 記錄句子分析使用
-    /// </summary>
-    public async Task RecordSentenceAnalysisAsync(Guid userId)
-    {
-        try
-        {
-            var today = DateOnly.FromDateTime(DateTime.Today);
-            var stats = await GetOrCreateTodayStatsAsync(userId, today);
-
-            stats.SentenceAnalysisCount++;
-            stats.TotalApiCalls++;
-            stats.UpdatedAt = DateTime.UtcNow;
-
-            await _context.SaveChangesAsync();
-
-            _logger.LogInformation("Recorded sentence analysis for user {UserId}, total today: {Count}",
-                userId, stats.SentenceAnalysisCount);
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error recording sentence analysis for user {UserId}", userId);
-        }
-    }
-
-    /// <summary>
-    /// 記錄單字查詢使用
-    /// </summary>
-    public async Task RecordWordQueryAsync(Guid userId, bool wasHighValue)
-    {
-        try
-        {
-            var today = DateOnly.FromDateTime(DateTime.Today);
-            var stats = await GetOrCreateTodayStatsAsync(userId, today);
-
-            if (wasHighValue)
-            {
-                stats.HighValueWordClicks++;
-            }
-            else
-            {
-                stats.LowValueWordClicks++;
-                stats.TotalApiCalls++; // 低價值詞彙需要API調用
-            }
-
-            stats.UniqueWordsQueried++; // 簡化：每次查詢都算一個獨特詞彙
-            stats.UpdatedAt = DateTime.UtcNow;
-
-            await _context.SaveChangesAsync();
-
-            _logger.LogInformation("Recorded word query for user {UserId}, high value: {IsHighValue}",
-                userId, wasHighValue);
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error recording word query for user {UserId}", userId);
-        }
-    }
-
-    /// <summary>
-    /// 獲取用戶使用統計
-    /// </summary>
-    public async Task<UserUsageStats> GetUsageStatsAsync(Guid userId)
-    {
-        try
-        {
-            var today = DateOnly.FromDateTime(DateTime.Today);
-            var resetTime = DateTime.UtcNow.AddHours(-FREE_USER_RESET_HOURS);
-
-            // 今日統計
-            var todayStats = await _context.WordQueryUsageStats
-                .FirstOrDefaultAsync(stats => stats.UserId == userId && stats.Date == today)
-                ?? new WordQueryUsageStats { UserId = userId, Date = today };
-
-            // 最近3小時使用量（用於限制檢查）
-            var recentUsage = await _context.WordQueryUsageStats
-                .Where(stats => stats.UserId == userId && stats.CreatedAt >= resetTime)
-                .SumAsync(stats => stats.SentenceAnalysisCount + stats.LowValueWordClicks);
-
-            // 本週統計
-            var weekStart = DateTime.Today.AddDays(-(int)DateTime.Today.DayOfWeek);
-            var weekStats = await _context.WordQueryUsageStats
-                .Where(stats => stats.UserId == userId && stats.Date >= DateOnly.FromDateTime(weekStart))
-                .GroupBy(stats => 1)
-                .Select(g => new
-                {
-                    TotalAnalysis = g.Sum(s => s.SentenceAnalysisCount),
-                    TotalWordClicks = g.Sum(s => s.HighValueWordClicks + s.LowValueWordClicks),
-                    TotalApiCalls = g.Sum(s => s.TotalApiCalls),
-                    UniqueWords = g.Sum(s => s.UniqueWordsQueried)
-                })
-                .FirstOrDefaultAsync();
-
-            return new UserUsageStats
-            {
-                UserId = userId,
-                Today = new DailyUsageStats
-                {
-                    Date = today,
-                    SentenceAnalysisCount = todayStats.SentenceAnalysisCount,
-                    HighValueWordClicks = todayStats.HighValueWordClicks,
-                    LowValueWordClicks = todayStats.LowValueWordClicks,
-                    TotalApiCalls = todayStats.TotalApiCalls,
-                    UniqueWordsQueried = todayStats.UniqueWordsQueried
-                },
-                RecentUsage = new UsageLimitInfo
-                {
-                    UsedInWindow = recentUsage,
-                    WindowLimit = FREE_USER_ANALYSIS_LIMIT,
-                    WindowHours = FREE_USER_RESET_HOURS,
-                    ResetTime = DateTime.UtcNow.AddHours(FREE_USER_RESET_HOURS -
-                        ((DateTime.UtcNow - resetTime).TotalHours % FREE_USER_RESET_HOURS))
-                },
-                ThisWeek = weekStats != null ? new WeeklyUsageStats
-                {
-                    StartDate = DateOnly.FromDateTime(weekStart),
-                    EndDate = DateOnly.FromDateTime(weekStart.AddDays(6)),
-                    TotalSentenceAnalysis = weekStats.TotalAnalysis,
-                    TotalWordClicks = weekStats.TotalWordClicks,
-                    TotalApiCalls = weekStats.TotalApiCalls,
-                    UniqueWordsQueried = weekStats.UniqueWords
-                } : new WeeklyUsageStats()
-            };
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error getting usage stats for user {UserId}", userId);
-            return new UserUsageStats { UserId = userId };
-        }
-    }
-
-    /// <summary>
-    /// 獲取或創建今日統計記錄
-    /// </summary>
-    private async Task<WordQueryUsageStats> GetOrCreateTodayStatsAsync(Guid userId, DateOnly date)
-    {
-        var stats = await _context.WordQueryUsageStats
-            .FirstOrDefaultAsync(s => s.UserId == userId && s.Date == date);
-
-        if (stats == null)
-        {
-            stats = new WordQueryUsageStats
-            {
-                Id = Guid.NewGuid(),
-                UserId = userId,
-                Date = date,
-                CreatedAt = DateTime.UtcNow,
-                UpdatedAt = DateTime.UtcNow
-            };
-
-            _context.WordQueryUsageStats.Add(stats);
-        }
-
-        return stats;
-    }
-}
-
-// 回應用的 DTO 類別
-public class UserUsageStats
-{
-    public Guid UserId { get; set; }
-    public DailyUsageStats Today { get; set; } = new();
-    public UsageLimitInfo RecentUsage { get; set; } = new();
-    public WeeklyUsageStats ThisWeek { get; set; } = new();
-}
-
-public class DailyUsageStats
-{
-    public DateOnly Date { get; set; }
-    public int SentenceAnalysisCount { get; set; }
-    public int HighValueWordClicks { get; set; }
-    public int LowValueWordClicks { get; set; }
-    public int TotalApiCalls { get; set; }
-    public int UniqueWordsQueried { get; set; }
-}
-
-public class UsageLimitInfo
-{
-    public int UsedInWindow { get; set; }
-    public int WindowLimit { get; set; }
-    public int WindowHours { get; set; }
-    public DateTime ResetTime { get; set; }
-    public bool CanUse => UsedInWindow < WindowLimit;
-    public int Remaining => Math.Max(0, WindowLimit - UsedInWindow);
-}
-
-public class WeeklyUsageStats
-{
-    public DateOnly StartDate { get; set; }
-    public DateOnly EndDate { get; set; }
-    public int TotalSentenceAnalysis { get; set; }
-    public int TotalWordClicks { get; set; }
-    public int TotalApiCalls { get; set; }
-    public int UniqueWordsQueried { get; set; }
-}

backend/DramaLing.Api/Services/Media/Audio/AudioCacheService.cs

@@ -1,147 +0,0 @@
-using System.Security.Cryptography;
-using System.Text;
-using Microsoft.EntityFrameworkCore;
-using DramaLing.Api.Data;
-using DramaLing.Api.Models.Entities;
-using DramaLing.Api.Models.Dtos;
-
-namespace DramaLing.Api.Services;
-
-public interface IAudioCacheService
-{
-    Task<TTSResponse> GetOrCreateAudioAsync(TTSRequest request);
-    Task<string> GenerateCacheKeyAsync(string text, string accent, string voice);
-    Task UpdateAccessTimeAsync(string cacheKey);
-    Task CleanupOldCacheAsync();
-}
-
-public class AudioCacheService : IAudioCacheService
-{
-    private readonly DramaLingDbContext _context;
-    private readonly IAzureSpeechService _speechService;
-    private readonly ILogger<AudioCacheService> _logger;
-
-    public AudioCacheService(
-        DramaLingDbContext context,
-        IAzureSpeechService speechService,
-        ILogger<AudioCacheService> logger)
-    {
-        _context = context;
-        _speechService = speechService;
-        _logger = logger;
-    }
-
-    public async Task<TTSResponse> GetOrCreateAudioAsync(TTSRequest request)
-    {
-        try
-        {
-            var cacheKey = await GenerateCacheKeyAsync(request.Text, request.Accent, request.Voice);
-
-            // 檢查快取
-            var cachedAudio = await _context.AudioCaches
-                .FirstOrDefaultAsync(a => a.TextHash == cacheKey);
-
-            if (cachedAudio != null)
-            {
-                // 更新訪問時間
-                await UpdateAccessTimeAsync(cacheKey);
-
-                return new TTSResponse
-                {
-                    AudioUrl = cachedAudio.AudioUrl,
-                    Duration = cachedAudio.DurationMs.HasValue ? cachedAudio.DurationMs.Value / 1000.0f : 0,
-                    CacheHit = true
-                };
-            }
-
-            // 生成新音頻
-            var response = await _speechService.GenerateAudioAsync(request);
-
-            if (!string.IsNullOrEmpty(response.Error))
-            {
-                return response;
-            }
-
-            // 存入快取
-            var audioCache = new AudioCache
-            {
-                TextHash = cacheKey,
-                TextContent = request.Text,
-                Accent = request.Accent,
-                VoiceId = request.Voice,
-                AudioUrl = response.AudioUrl,
-                DurationMs = (int)(response.Duration * 1000),
-                CreatedAt = DateTime.UtcNow,
-                LastAccessed = DateTime.UtcNow,
-                AccessCount = 1
-            };
-
-            _context.AudioCaches.Add(audioCache);
-            await _context.SaveChangesAsync();
-
-            _logger.LogInformation("Created new audio cache entry for text: {Text}", request.Text);
-
-            return response;
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error in GetOrCreateAudioAsync for text: {Text}", request.Text);
-            return new TTSResponse
-            {
-                Error = "Internal error processing audio request"
-            };
-        }
-    }
-
-    public async Task<string> GenerateCacheKeyAsync(string text, string accent, string voice)
-    {
-        var combined = $"{text}|{accent}|{voice}";
-        using var sha256 = SHA256.Create();
-        var hash = sha256.ComputeHash(Encoding.UTF8.GetBytes(combined));
-        return Convert.ToHexString(hash).ToLowerInvariant();
-    }
-
-    public async Task UpdateAccessTimeAsync(string cacheKey)
-    {
-        try
-        {
-            var audioCache = await _context.AudioCaches
-                .FirstOrDefaultAsync(a => a.TextHash == cacheKey);
-
-            if (audioCache != null)
-            {
-                audioCache.LastAccessed = DateTime.UtcNow;
-                audioCache.AccessCount++;
-                await _context.SaveChangesAsync();
-            }
-        }
-        catch (Exception ex)
-        {
-            _logger.LogWarning(ex, "Failed to update access time for cache key: {CacheKey}", cacheKey);
-        }
-    }
-
-    public async Task CleanupOldCacheAsync()
-    {
-        try
-        {
-            var cutoffDate = DateTime.UtcNow.AddDays(-30);
-
-            var oldEntries = await _context.AudioCaches
-                .Where(a => a.LastAccessed < cutoffDate)
-                .ToListAsync();
-
-            if (oldEntries.Any())
-            {
-                _context.AudioCaches.RemoveRange(oldEntries);
-                await _context.SaveChangesAsync();
-
-                _logger.LogInformation("Cleaned up {Count} old audio cache entries", oldEntries.Count);
-            }
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error during audio cache cleanup");
-        }
-    }
-}

backend/DramaLing.Api/Services/Media/Audio/AzureSpeechService.cs

@@ -1,191 +0,0 @@
-using DramaLing.Api.Models.Dtos;
-using System.Text;
-using System.Security.Cryptography;
-
-namespace DramaLing.Api.Services;
-
-public interface IAzureSpeechService
-{
-    Task<TTSResponse> GenerateAudioAsync(TTSRequest request);
-    Task<PronunciationResponse> EvaluatePronunciationAsync(Stream audioStream, PronunciationRequest request);
-}
-
-public class AzureSpeechService : IAzureSpeechService
-{
-    private readonly IConfiguration _configuration;
-    private readonly ILogger<AzureSpeechService> _logger;
-    private readonly bool _isConfigured;
-
-    public AzureSpeechService(IConfiguration configuration, ILogger<AzureSpeechService> logger)
-    {
-        _configuration = configuration;
-        _logger = logger;
-
-        var subscriptionKey = _configuration["Azure:Speech:SubscriptionKey"];
-        var region = _configuration["Azure:Speech:Region"];
-
-        if (string.IsNullOrEmpty(subscriptionKey) || string.IsNullOrEmpty(region))
-        {
-            _logger.LogWarning("Azure Speech configuration is missing. TTS functionality will be disabled.");
-            _isConfigured = false;
-            return;
-        }
-
-        _isConfigured = true;
-        _logger.LogInformation("Azure Speech service configured for region: {Region}", region);
-    }
-
-    public async Task<TTSResponse> GenerateAudioAsync(TTSRequest request)
-    {
-        try
-        {
-            if (!_isConfigured)
-            {
-                return new TTSResponse
-                {
-                    Error = "Azure Speech service is not configured"
-                };
-            }
-
-            // 模擬 TTS 處理，返回模擬數據
-            await Task.Delay(500); // 模擬 API 延遲
-
-            // 生成模擬的 base64 音頻數據 (實際上是空的 MP3 標頭)
-            var mockAudioData = Convert.ToBase64String(new byte[] {
-                0xFF, 0xFB, 0x90, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
-            });
-            var audioUrl = $"data:audio/mp3;base64,{mockAudioData}";
-
-            return new TTSResponse
-            {
-                AudioUrl = audioUrl,
-                Duration = CalculateAudioDuration(request.Text.Length),
-                CacheHit = false
-            };
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error generating audio for text: {Text}", request.Text);
-            return new TTSResponse
-            {
-                Error = "Internal error generating audio"
-            };
-        }
-    }
-
-    public async Task<PronunciationResponse> EvaluatePronunciationAsync(Stream audioStream, PronunciationRequest request)
-    {
-        try
-        {
-            if (!_isConfigured)
-            {
-                return new PronunciationResponse
-                {
-                    Error = "Azure Speech service is not configured"
-                };
-            }
-
-            // 模擬語音評估處理
-            await Task.Delay(2000); // 模擬 API 調用延遲
-
-            // 生成模擬的評分數據
-            var random = new Random();
-            var overallScore = random.Next(75, 95);
-
-            return new PronunciationResponse
-            {
-                OverallScore = overallScore,
-                Accuracy = (float)(random.NextDouble() * 20 + 75),
-                Fluency = (float)(random.NextDouble() * 20 + 75),
-                Completeness = (float)(random.NextDouble() * 20 + 75),
-                Prosody = (float)(random.NextDouble() * 20 + 75),
-                PhonemeScores = GenerateMockPhonemeScores(request.TargetText),
-                Suggestions = GenerateMockSuggestions(overallScore)
-            };
-        }
-        catch (Exception ex)
-        {
-            _logger.LogError(ex, "Error evaluating pronunciation for text: {Text}", request.TargetText);
-            return new PronunciationResponse
-            {
-                Error = "Internal error evaluating pronunciation"
-            };
-        }
-    }
-
-    private List<PhonemeScore> GenerateMockPhonemeScores(string text)
-    {
-        var phonemes = new List<PhonemeScore>();
-        var words = text.Split(' ', StringSplitOptions.RemoveEmptyEntries);
-
-        foreach (var word in words.Take(3)) // 只處理前3個詞
-        {
-            phonemes.Add(new PhonemeScore
-            {
-                Phoneme = $"/{word[0]}/",
-                Score = Random.Shared.Next(70, 95),
-                Suggestion = Random.Shared.Next(0, 3) == 0 ? $"注意 {word} 的發音" : null
-            });
-        }
-
-        return phonemes;
-    }
-
-    private List<string> GenerateMockSuggestions(int overallScore)
-    {
-        var suggestions = new List<string>();
-
-        if (overallScore < 85)
-        {
-            suggestions.Add("注意單詞的重音位置");
-        }
-
-        if (overallScore < 80)
-        {
-            suggestions.Add("發音可以更清晰一些");
-            suggestions.Add("嘗試放慢語速，確保每個音都發準");
-        }
-
-        if (overallScore >= 90)
-        {
-            suggestions.Add("發音很棒！繼續保持");
-        }
-
-        return suggestions;
-    }
-
-    private string GetVoiceName(string accent, string voicePreference)
-    {
-        return accent.ToLower() switch
-        {
-            "uk" => "en-GB-SoniaNeural",
-            "us" => "en-US-AriaNeural",
-            _ => "en-US-AriaNeural"
-        };
-    }
-
-    private string CreateSSML(string text, string voice, float speed)
-    {
-        var rate = speed switch
-        {
-            < 0.8f => "slow",
-            > 1.2f => "fast",
-            _ => "medium"
-        };
-
-        return $@"
-        <speak version='1.0' xmlns='http://www.w3.org/2001/10/synthesis' xml:lang='en-US'>
-            <voice name='{voice}'>
-                <prosody rate='{rate}'>
-                    {text}
-                </prosody>
-            </voice>
-        </speak>";
-    }
-
-    private float CalculateAudioDuration(int textLength)
-    {
-        // 根據文字長度估算音頻時長：平均每個字符 0.1 秒
-        return Math.Max(1.0f, textLength * 0.1f);
-    }
-}