dramaling-vocab-learning/backend/DramaLing.Api/Services/AI/Gemini/SentenceAnalyzer.cs

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

namespace DramaLing.Api.Services.AI.Gemini;

/// <summary>
/// 句子分析服務實作
/// </summary>
public class SentenceAnalyzer : ISentenceAnalyzer
{
    private readonly IGeminiClient _geminiClient;
    private readonly ILogger<SentenceAnalyzer> _logger;

    public SentenceAnalyzer(
        IGeminiClient geminiClient,
        ILogger<SentenceAnalyzer> logger)
    {
        _geminiClient = geminiClient ?? throw new ArgumentNullException(nameof(geminiClient));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

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

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

            var prompt = BuildAnalysisPrompt(inputText);
            var aiResponse = await _geminiClient.CallGeminiAPIAsync(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"))
            {
                _logger.LogWarning("Using safety filtering fallback response");
            }

            var analysisData = CreateAnalysisFromAIResponse(inputText, 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 string BuildAnalysisPrompt(string inputText)
    {
        return $@"You are an English learning assistant. Analyze this sentence and return ONLY a valid JSON response.

**Input Sentence**: ""{inputText}""

**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/adverb/pronoun/preposition/conjunction/interjection"",
      ""pronunciation"": ""/phonetic/"",
      ""CEFR"": ""A1/A2/B1/B2/C1/C2"",
      ""frequency"": ""high/medium/low"",
      ""synonyms"": [""synonym1"", ""synonym2""],
      ""example"": ""example sentence"",
      ""exampleTranslation"": ""Traditional Chinese example translation""
    }}
  }},
  ""idioms"": [
    {{
      ""idiom"": ""idiomatic expression"",
      ""translation"": ""Traditional Chinese meaning"",
      ""definition"": ""English explanation"",
      ""pronunciation"": ""/phonetic notation/"",
      ""CEFR"": ""A1/A2/B1/B2/C1/C2"",
      ""frequency"": ""high/medium/low"",
      ""synonyms"": [""synonym1"", ""synonym2""],
      ""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.";
    }

    private SentenceAnalysisData CreateAnalysisFromAIResponse(string inputText, 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()),
                Idioms = ConvertIdioms(aiAnalysis.Idioms ?? new()),
                GrammarCorrection = ConvertGrammarCorrection(aiAnalysis),
                Metadata = new AnalysisMetadata
                {
                    ProcessingDate = DateTime.UtcNow,
                    AnalysisModel = "gemini-1.5-flash",
                    AnalysisVersion = "2.0"
                }
            };

            return analysisData;
        }
        catch (JsonException ex)
        {
            _logger.LogError(ex, "Failed to parse AI response as JSON: {Response}", aiResponse);
            return CreateFallbackAnalysis(inputText, 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}/",
                DifficultyLevelNumeric = CEFRHelper.ToNumeric(aiWord.CEFR ?? "A0"),
                CEFR = aiWord.CEFR ?? "A0",
                Frequency = aiWord.Frequency ?? "medium",
                Synonyms = aiWord.Synonyms ?? new List<string>(),
                Example = aiWord.Example,
                ExampleTranslation = aiWord.ExampleTranslation,
            };
        }

        return result;
    }

    private List<IdiomDto> ConvertIdioms(List<AiIdiom> aiIdioms)
    {
        var result = new List<IdiomDto>();

        foreach (var aiIdiom in aiIdioms)
        {
            result.Add(new IdiomDto
            {
                Idiom = aiIdiom.Idiom ?? "",
                Translation = aiIdiom.Translation ?? "",
                Definition = aiIdiom.Definition ?? "",
                Pronunciation = aiIdiom.Pronunciation ?? "",
                DifficultyLevelNumeric = CEFRHelper.ToNumeric(aiIdiom.CEFR ?? "A0"),
                CEFR = aiIdiom.CEFR ?? "A0",
                Frequency = aiIdiom.Frequency ?? "medium",
                Synonyms = aiIdiom.Synonyms ?? new List<string>(),
                Example = aiIdiom.Example,
                ExampleTranslation = aiIdiom.ExampleTranslation
            });
        }

        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 }
        }).ToList();

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

    private SentenceAnalysisData CreateFallbackAnalysis(string inputText, 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
            {
                ProcessingDate = DateTime.UtcNow,
                AnalysisModel = "gemini-1.5-flash-fallback",
                AnalysisVersion = "2.0"
            },
        };
    }

    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 = ExtractTranslationFromAI(cleanWord, aiResponse),
                Definition = $"Please refer to the AI analysis above for detailed definition.",
                PartOfSpeech = "unknown",
                Pronunciation = $"/{cleanWord}/",
                DifficultyLevelNumeric = EstimateBasicDifficultyNumeric(cleanWord),
                Frequency = "medium",
                Synonyms = new List<string>(),
                Example = null,
                ExampleTranslation = null,
            };
        }

        return result;
    }

    private string ExtractTranslationFromAI(string word, string aiResponse)
    {
        if (aiResponse.Contains(word, StringComparison.OrdinalIgnoreCase))
        {
            return $"{word} translation from AI";
        }
        return $"{word} - 請查看完整分析";
    }

    private int EstimateBasicDifficultyNumeric(string word)
    {
        var a1Words = new[] { "i", "you", "he", "she", "it", "we", "they", "the", "a", "an", "is", "are", "was", "were", "have", "do", "go", "get", "see", "know" };
        var a2Words = new[] { "make", "think", "come", "take", "use", "work", "call", "try", "ask", "need", "feel", "become", "leave", "put", "say", "tell", "turn", "move" };

        var lowerWord = word.ToLower();
        if (a1Words.Contains(lowerWord)) return 1; // A1
        if (a2Words.Contains(lowerWord)) return 2; // A2
        if (word.Length <= 4) return 2; // A2
        if (word.Length <= 6) return 3; // B1
        return 4; // B2
    }
}

// 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? CEFR { 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? Idiom { get; set; }
    public string? Translation { get; set; }
    public string? Definition { get; set; }
    public string? Pronunciation { get; set; }
    public string? CEFR { get; set; }
    public string? Frequency { get; set; }
    public List<string>? Synonyms { get; set; }
    public string? Example { get; set; }
    public string? ExampleTranslation { get; set; }
}