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

using System.Text.RegularExpressions;

namespace DramaLing.Api.Services;

public interface IBlankGenerationService
{
    Task<string?> GenerateBlankQuestionAsync(string word, string example);
    string? TryProgrammaticBlank(string word, string example);
    Task<string?> GenerateAIBlankAsync(string word, string example);
    bool HasValidBlank(string blankQuestion);
}

public class BlankGenerationService : IBlankGenerationService
{
    private readonly IWordVariationService _wordVariationService;
    private readonly IGeminiService _geminiService;
    private readonly ILogger<BlankGenerationService> _logger;

    public BlankGenerationService(
        IWordVariationService wordVariationService,
        IGeminiService geminiService,
        ILogger<BlankGenerationService> logger)
    {
        _wordVariationService = wordVariationService;
        _geminiService = geminiService;
        _logger = logger;
    }

    public async Task<string?> GenerateBlankQuestionAsync(string word, string example)
    {
        if (string.IsNullOrEmpty(word) || string.IsNullOrEmpty(example))
        {
            _logger.LogWarning("Invalid input - word or example is null/empty");
            return null;
        }

        _logger.LogInformation("Generating blank question for word: {Word}, example: {Example}",
            word, example);

        // Step 1: 嘗試程式碼挖空
        var programmaticResult = TryProgrammaticBlank(word, example);
        if (!string.IsNullOrEmpty(programmaticResult))
        {
            _logger.LogInformation("Successfully generated programmatic blank for word: {Word}", word);
            return programmaticResult;
        }

        // Step 2: 程式碼挖空失敗，嘗試 AI 挖空
        _logger.LogInformation("Programmatic blank failed for word: {Word}, trying AI blank", word);
        var aiResult = await GenerateAIBlankAsync(word, example);

        if (!string.IsNullOrEmpty(aiResult))
        {
            _logger.LogInformation("Successfully generated AI blank for word: {Word}", word);
            return aiResult;
        }

        _logger.LogWarning("Both programmatic and AI blank generation failed for word: {Word}", word);
        return null;
    }

    public string? TryProgrammaticBlank(string word, string example)
    {
        try
        {
            _logger.LogDebug("Attempting programmatic blank for word: {Word}", word);

            // 1. 完全匹配 (不區分大小寫)
            var exactMatch = Regex.Replace(example, $@"\b{Regex.Escape(word)}\b", "____", RegexOptions.IgnoreCase);
            if (exactMatch != example)
            {
                _logger.LogDebug("Exact match blank successful for word: {Word}", word);
                return exactMatch;
            }

            // 2. 常見變形處理
            var variations = _wordVariationService.GetCommonVariations(word);
            foreach(var variation in variations)
            {
                var variantMatch = Regex.Replace(example, $@"\b{Regex.Escape(variation)}\b", "____", RegexOptions.IgnoreCase);
                if (variantMatch != example)
                {
                    _logger.LogDebug("Variation match blank successful for word: {Word}, variation: {Variation}",
                        word, variation);
                    return variantMatch;
                }
            }

            _logger.LogDebug("Programmatic blank failed for word: {Word}", word);
            return null; // 挖空失敗
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error in programmatic blank for word: {Word}", word);
            return null;
        }
    }

    public async Task<string?> GenerateAIBlankAsync(string word, string example)
    {
        try
        {
            var prompt = $@"
請將以下例句中與詞彙「{word}」相關的詞挖空，用____替代：

詞彙: {word}
例句: {example}

規則:
1. 只挖空與目標詞彙相關的詞(包含變形、時態、複數等)
2. 用____替代被挖空的詞
3. 保持句子其他部分不變
4. 直接返回挖空後的句子，不要額外說明

挖空後的句子:";

            _logger.LogInformation("Generating AI blank for word: {Word}, example: {Example}",
                word, example);

            // 暫時使用程式碼邏輯，AI 功能將在後續版本實現
            // TODO: 整合 Gemini API 進行智能挖空
            _logger.LogInformation("AI blank generation not yet implemented, returning null");
            return null;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Error generating AI blank for word: {Word}", word);
            return null;
        }
    }

    public bool HasValidBlank(string blankQuestion)
    {
        var isValid = !string.IsNullOrEmpty(blankQuestion) && blankQuestion.Contains("____");
        _logger.LogDebug("Validating blank question: {IsValid}", isValid);
        return isValid;
    }
}