dramaling-vocab-learning/backend/DramaLing.Api/Services/GeminiService.cs

using DramaLing.Api.Models.DTOs;
using System.Text.Json;
using System.Text;

namespace DramaLing.Api.Services;

public interface IGeminiService
{
    Task<SentenceAnalysisData> AnalyzeSentenceAsync(string inputText, string userLevel, AnalysisOptions options);
}

public class GeminiService : IGeminiService
{
    private readonly HttpClient _httpClient;
    private readonly ILogger<GeminiService> _logger;
    private readonly string _apiKey;

    public GeminiService(HttpClient httpClient, IConfiguration configuration, ILogger<GeminiService> logger)
    {
        _httpClient = httpClient;
        _logger = logger;

        _apiKey = Environment.GetEnvironmentVariable("GEMINI_API_KEY")
                 ?? configuration["AI:GeminiApiKey"]
                 ?? configuration["Gemini:ApiKey"]
                 ?? throw new InvalidOperationException("Gemini API Key not configured");

        _logger.LogInformation("GeminiService initialized with API key: {ApiKeyStart}...",
            _apiKey.Length > 10 ? _apiKey.Substring(0, 10) : "[key-not-set]");

        _httpClient.DefaultRequestHeaders.Add("User-Agent", "DramaLing/1.0");
    }

    public async Task<SentenceAnalysisData> AnalyzeSentenceAsync(string inputText, string userLevel, AnalysisOptions options)
    {
        var startTime = DateTime.UtcNow;

        try
        {
            _logger.LogInformation("Starting sentence analysis for text: {Text}, UserLevel: {UserLevel}",
                inputText.Substring(0, Math.Min(50, inputText.Length)), userLevel);

            // 符合產品需求規格的結構化 prompt
            var prompt = $@"You are an English learning assistant. Analyze this sentence for a {userLevel} CEFR level learner and return ONLY a valid JSON response.

**Input Sentence**: ""{inputText}""
**Learner Level**: {userLevel}

**Required JSON Structure:**
{{
  ""sentenceTranslation"": ""Traditional Chinese translation of the entire sentence"",
  ""hasGrammarErrors"": true/false,
  ""grammarCorrections"": [
    {{
      ""original"": ""incorrect text"",
      ""corrected"": ""correct text"",
      ""type"": ""error type (tense/subject-verb/preposition/word-order)"",
      ""explanation"": ""brief explanation in Traditional Chinese""
    }}
  ],
  ""vocabularyAnalysis"": {{
    ""word1"": {{
      ""word"": ""the word"",
      ""translation"": ""Traditional Chinese translation"",
      ""definition"": ""English definition"",
      ""partOfSpeech"": ""noun/verb/adjective/etc"",
      ""pronunciation"": ""/phonetic/"",
      ""difficultyLevel"": ""A1/A2/B1/B2/C1/C2"",
      ""isIdiom"": false,
      ""frequency"": ""high/medium/low"",
      ""synonyms"": [""synonym1"", ""synonym2""],
      ""example"": ""example sentence"",
      ""exampleTranslation"": ""Traditional Chinese example translation""
    }}
  }},
  ""idioms"": [
    {{
      ""phrase"": ""idiomatic expression"",
      ""translation"": ""Traditional Chinese meaning"",
      ""definition"": ""English explanation"",
      ""example"": ""usage example"",
      ""exampleTranslation"": ""Traditional Chinese example""
    }}
  ]
}}

**Analysis Guidelines:**
1. **Grammar Check**: Detect tense errors, subject-verb agreement, preposition usage, word order
2. **Vocabulary Analysis**: Include ALL significant words (exclude articles: a, an, the)
3. **CEFR Levels**: Assign accurate A1-C2 levels for each word
4. **Idioms**: Identify any idiomatic expressions or phrasal verbs
5. **Translations**: Use Traditional Chinese (Taiwan standard)

**IMPORTANT**: Return ONLY the JSON object, no additional text or explanation.";

            var aiResponse = await CallGeminiAPI(prompt);

            _logger.LogInformation("Gemini AI response received: {ResponseLength} characters", aiResponse?.Length ?? 0);

            if (string.IsNullOrWhiteSpace(aiResponse))
            {
                throw new InvalidOperationException("Gemini API returned empty response");
            }

            // 檢查是否是安全過濾的回退訊息
            if (aiResponse.Contains("temporarily unavailable due to safety filtering"))
            {
                // 這是安全過濾的情況，但我們仍然要處理它而不是拋出異常
                _logger.LogWarning("Using safety filtering fallback response");
            }

            // 直接使用 AI 的回應創建分析數據
            var analysisData = CreateAnalysisFromAIResponse(inputText, userLevel, aiResponse);

            var processingTime = (DateTime.UtcNow - startTime).TotalSeconds;
            _logger.LogInformation("Sentence analysis completed in {ProcessingTime}s", processingTime);

            return analysisData;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error analyzing sentence: {Text}", inputText);
            throw;
        }
    }

    private SentenceAnalysisData CreateAnalysisFromAIResponse(string inputText, string userLevel, string aiResponse)
    {
        _logger.LogInformation("Creating analysis from AI response: {ResponsePreview}...",
            aiResponse.Substring(0, Math.Min(100, aiResponse.Length)));

        try
        {
            // 清理 AI 回應以確保是純 JSON
            var cleanJson = aiResponse.Trim();
            if (cleanJson.StartsWith("```json"))
            {
                cleanJson = cleanJson.Substring(7);
            }
            if (cleanJson.EndsWith("```"))
            {
                cleanJson = cleanJson.Substring(0, cleanJson.Length - 3);
            }

            // 解析 AI 回應的 JSON
            var aiAnalysis = JsonSerializer.Deserialize<AiAnalysisResponse>(cleanJson, new JsonSerializerOptions
            {
                PropertyNameCaseInsensitive = true
            });

            if (aiAnalysis == null)
            {
                throw new InvalidOperationException("Failed to parse AI response JSON");
            }

            // 轉換為 DTO 結構
            var analysisData = new SentenceAnalysisData
            {
                OriginalText = inputText,
                SentenceMeaning = aiAnalysis.SentenceTranslation ?? "",
                VocabularyAnalysis = ConvertVocabularyAnalysis(aiAnalysis.VocabularyAnalysis ?? new()),
                GrammarCorrection = ConvertGrammarCorrection(aiAnalysis),
                Metadata = new AnalysisMetadata
                {
                    UserLevel = userLevel,
                    ProcessingDate = DateTime.UtcNow,
                    AnalysisModel = "gemini-1.5-flash",
                    AnalysisVersion = "2.0"
                }
            };

            // 計算統計
            analysisData.Statistics = CalculateStatistics(analysisData.VocabularyAnalysis, userLevel);

            return analysisData;
        }
        catch (JsonException ex)
        {
            _logger.LogError(ex, "Failed to parse AI response as JSON: {Response}", aiResponse);
            // 回退到舊的處理方式
            return CreateFallbackAnalysis(inputText, userLevel, aiResponse);
        }
    }

    private Dictionary<string, VocabularyAnalysisDto> ConvertVocabularyAnalysis(Dictionary<string, AiVocabularyAnalysis> aiVocab)
    {
        var result = new Dictionary<string, VocabularyAnalysisDto>();

        foreach (var kvp in aiVocab)
        {
            var aiWord = kvp.Value;
            result[kvp.Key] = new VocabularyAnalysisDto
            {
                Word = aiWord.Word ?? kvp.Key,
                Translation = aiWord.Translation ?? "",
                Definition = aiWord.Definition ?? "",
                PartOfSpeech = aiWord.PartOfSpeech ?? "unknown",
                Pronunciation = aiWord.Pronunciation ?? $"/{kvp.Key}/",
                DifficultyLevel = aiWord.DifficultyLevel ?? "A2",
                IsIdiom = aiWord.IsIdiom,
                Frequency = aiWord.Frequency ?? "medium",
                Synonyms = aiWord.Synonyms ?? new List<string>(),
                Example = aiWord.Example,
                ExampleTranslation = aiWord.ExampleTranslation,
                Tags = new List<string> { "ai-analyzed", "gemini" }
            };
        }

        return result;
    }

    private GrammarCorrectionDto? ConvertGrammarCorrection(AiAnalysisResponse aiAnalysis)
    {
        if (!aiAnalysis.HasGrammarErrors || aiAnalysis.GrammarCorrections == null || !aiAnalysis.GrammarCorrections.Any())
        {
            return null;
        }

        var corrections = aiAnalysis.GrammarCorrections.Select(gc => new GrammarErrorDto
        {
            Error = gc.Original ?? "",
            Correction = gc.Corrected ?? "",
            Type = gc.Type ?? "grammar",
            Explanation = gc.Explanation ?? "",
            Severity = "medium",
            Position = new ErrorPosition { Start = 0, End = 0 } // 簡化處理
        }).ToList();

        return new GrammarCorrectionDto
        {
            HasErrors = true,
            CorrectedText = string.Join(" ", corrections.Select(c => c.Correction)),
            Corrections = corrections
        };
    }

    private SentenceAnalysisData CreateFallbackAnalysis(string inputText, string userLevel, string aiResponse)
    {
        _logger.LogWarning("Using fallback analysis due to JSON parsing failure");

        return new SentenceAnalysisData
        {
            OriginalText = inputText,
            SentenceMeaning = aiResponse,
            VocabularyAnalysis = CreateBasicVocabularyFromText(inputText, aiResponse),
            Metadata = new AnalysisMetadata
            {
                UserLevel = userLevel,
                ProcessingDate = DateTime.UtcNow,
                AnalysisModel = "gemini-1.5-flash-fallback",
                AnalysisVersion = "1.0"
            },
            Statistics = new AnalysisStatistics()
        };
    }

    private Dictionary<string, VocabularyAnalysisDto> CreateBasicVocabularyFromText(string inputText, string aiResponse)
    {
        var words = inputText.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        var result = new Dictionary<string, VocabularyAnalysisDto>();

        foreach (var word in words.Take(15))
        {
            var cleanWord = word.ToLower().Trim('.', ',', '!', '?', ';', ':', '"', '\'');
            if (string.IsNullOrEmpty(cleanWord) || cleanWord.Length < 2) continue;

            result[cleanWord] = new VocabularyAnalysisDto
            {
                Word = cleanWord,
                Translation = $"{cleanWord} - AI分析請查看上方詳細說明",
                Definition = $"Definition in AI analysis above",
                PartOfSpeech = "word",
                Pronunciation = $"/{cleanWord}/",
                DifficultyLevel = EstimateBasicDifficulty(cleanWord),
                IsIdiom = false, // 統一使用 IsIdiom
                Frequency = "medium",
                Synonyms = new List<string>(),
                Example = $"See AI analysis for {cleanWord}",
                ExampleTranslation = "詳見上方AI分析",
                Tags = new List<string> { "ai-analyzed" }
            };
        }

        return result;
    }

    private string EstimateBasicDifficulty(string word)
    {
        var basicWords = new[] { "i", "you", "he", "she", "it", "we", "they", "the", "a", "an", "is", "are", "was", "were" };
        return basicWords.Contains(word.ToLower()) ? "A1" : "A2";
    }

    private AnalysisStatistics CalculateStatistics(Dictionary<string, VocabularyAnalysisDto> vocabulary, string userLevel)
    {
        var stats = new AnalysisStatistics
        {
            TotalWords = vocabulary.Count,
            UniqueWords = vocabulary.Count,
            SimpleWords = vocabulary.Count(kvp => kvp.Value.DifficultyLevel == "A1"),
            ModerateWords = vocabulary.Count(kvp => kvp.Value.DifficultyLevel == "A2"),
            DifficultWords = vocabulary.Count(kvp => !new[] { "A1", "A2" }.Contains(kvp.Value.DifficultyLevel)),
            Idioms = vocabulary.Count(kvp => kvp.Value.IsIdiom), // 統一使用 Idioms
            AverageDifficulty = userLevel
        };

        return stats;
    }

    private async Task<string> CallGeminiAPI(string prompt)
    {
        try
        {
            var requestBody = new
            {
                contents = new[]
                {
                    new
                    {
                        parts = new[]
                        {
                            new { text = prompt }
                        }
                    }
                },
                generationConfig = new
                {
                    temperature = 0.7,
                    topK = 40,
                    topP = 0.95,
                    maxOutputTokens = 2000
                }
            };

            var json = JsonSerializer.Serialize(requestBody);
            var content = new StringContent(json, Encoding.UTF8, "application/json");

            var response = await _httpClient.PostAsync($"https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash:generateContent?key={_apiKey}", content);
            response.EnsureSuccessStatusCode();

            var responseJson = await response.Content.ReadAsStringAsync();
            _logger.LogInformation("Raw Gemini API response: {Response}", responseJson.Substring(0, Math.Min(500, responseJson.Length)));

            var geminiResponse = JsonSerializer.Deserialize<GeminiApiResponse>(responseJson);

            // Check for safety filter blocking
            if (geminiResponse?.PromptFeedback != null)
            {
                _logger.LogWarning("Gemini prompt feedback received: {Feedback}", JsonSerializer.Serialize(geminiResponse.PromptFeedback));
            }

            // 詳細調試信息
            _logger.LogInformation("Gemini response candidates count: {Count}", geminiResponse?.Candidates?.Count ?? 0);
            var firstCandidate = geminiResponse?.Candidates?.FirstOrDefault();
            _logger.LogInformation("First candidate content: {HasContent}", firstCandidate?.Content != null);
            _logger.LogInformation("First candidate parts count: {Count}", firstCandidate?.Content?.Parts?.Count ?? 0);

            // Try to get response text
            var aiText = geminiResponse?.Candidates?.FirstOrDefault()?.Content?.Parts?.FirstOrDefault()?.Text ?? string.Empty;

            _logger.LogInformation("Gemini API returned: {ResponseLength} characters", aiText.Length);
            if (!string.IsNullOrEmpty(aiText))
            {
                _logger.LogInformation("AI text preview: {Preview}", aiText.Substring(0, Math.Min(200, aiText.Length)));
            }

            // If no text but we have a successful response, it might be safety filtered
            if (string.IsNullOrWhiteSpace(aiText) && geminiResponse?.PromptFeedback != null)
            {
                // Return a fallback response instead of throwing
                return "The content analysis is temporarily unavailable due to safety filtering. Please try with different content.";
            }

            return aiText;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Gemini API call failed");
            throw;
        }
    }
}

// Gemini API response models
internal class GeminiApiResponse
{
    public List<GeminiCandidate>? Candidates { get; set; }
    public object? PromptFeedback { get; set; }
}

internal class GeminiCandidate
{
    public GeminiContent? Content { get; set; }
}

internal class GeminiContent
{
    public List<GeminiPart>? Parts { get; set; }
}

internal class GeminiPart
{
    public string? Text { get; set; }
}

// AI Response JSON Models
internal class AiAnalysisResponse
{
    public string? SentenceTranslation { get; set; }
    public bool HasGrammarErrors { get; set; }
    public List<AiGrammarCorrection>? GrammarCorrections { get; set; }
    public Dictionary<string, AiVocabularyAnalysis>? VocabularyAnalysis { get; set; }
    public List<AiIdiom>? Idioms { get; set; }
}

internal class AiGrammarCorrection
{
    public string? Original { get; set; }
    public string? Corrected { get; set; }
    public string? Type { get; set; }
    public string? Explanation { get; set; }
}

internal class AiVocabularyAnalysis
{
    public string? Word { get; set; }
    public string? Translation { get; set; }
    public string? Definition { get; set; }
    public string? PartOfSpeech { get; set; }
    public string? Pronunciation { get; set; }
    public string? DifficultyLevel { get; set; }
    public bool IsIdiom { get; set; }
    public string? Frequency { get; set; }
    public List<string>? Synonyms { get; set; }
    public string? Example { get; set; }
    public string? ExampleTranslation { get; set; }
}

internal class AiIdiom
{
    public string? Phrase { get; set; }
    public string? Translation { get; set; }
    public string? Definition { get; set; }
    public string? Example { get; set; }
    public string? ExampleTranslation { get; set; }
}