DeutschLernen/GermanApp/Application/Services/StoryGenerationService.cs

using GermanApp.Domain.Interfaces;
using Microsoft.Extensions.Logging;

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for generating stories using Mistral AI.
/// This is part of the Application layer.
/// </summary>
public class StoryGenerationService
{
    private readonly IMistralService _mistralService;
    private readonly ILogger<StoryGenerationService> _logger;

    /// <summary>
    /// Creates a new StoryGenerationService.
    /// </summary>
    /// <param name="mistralService">The Mistral text generation service</param>
    /// <param name="logger">Logger for service operations</param>
    public StoryGenerationService(
        IMistralService mistralService,
        ILogger<StoryGenerationService> logger)
    {
        _mistralService = mistralService;
        _logger = logger;
    }

    /// <summary>
    /// Generates a story based on the given parameters.
    /// </summary>
    /// <param name="level">The CEFR level (A1, A2, B1, B2, C1)</param>
    /// <param name="topic">The story topic or theme</param>
    /// <param name="vocabularyWords">List of German vocabulary words to include in the story</param>
    /// <param name="length">Approximate word count for the story</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The generated story text in German</returns>
    public virtual async Task<string> GenerateStoryAsync(
        string level,
        string topic,
        IReadOnlyList<string> vocabularyWords,
        int length = 200,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Generating story: Level={Level}, Topic={Topic}, VocabularyCount={Count}, Length={Length}",
            level, topic, vocabularyWords?.Count ?? 0, length);

        try
        {
            var story = await _mistralService.GenerateStoryAsync(
                level,
                topic,
                vocabularyWords,
                length,
                cancellationToken);

            // Validate the generated story
            ValidateStory(story, level, vocabularyWords);

            _logger.LogInformation("Story generated successfully");
            return story;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to generate story");
            throw new AiServiceException(
                "Failed to generate story: " + ex.Message,
                AiErrorCode.Temporary);
        }
    }

    /// <summary>
    /// Generates a story for a specific lesson.
    /// </summary>
    /// <param name="lessonTitle">The lesson title for context</param>
    /// <param name="level">The CEFR level</param>
    /// <param name="vocabularyWords">List of vocabulary words from the lesson</param>
    /// <param name="length">Approximate word count</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The generated story text</returns>
    public virtual async Task<string> GenerateLessonStoryAsync(
        string lessonTitle,
        string level,
        IReadOnlyList<string> vocabularyWords,
        int length = 250,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Generating lesson story: Lesson={Lesson}, Level={Level}, VocabularyCount={Count}",
            lessonTitle, level, vocabularyWords?.Count ?? 0);

        return await GenerateStoryAsync(
            level,
            lessonTitle,
            vocabularyWords,
            length,
            cancellationToken);
    }

    /// <summary>
    /// Generates multiple stories for different levels.
    /// </summary>
    /// <param name="topic">The common topic for all stories</param>
    /// <param name="vocabularyByLevel">Dictionary mapping CEFR levels to vocabulary words</param>
    /// <param name="lengthByLevel">Dictionary mapping CEFR levels to story lengths</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Dictionary mapping levels to generated stories</returns>
    public virtual async Task<IDictionary<string, string>> GenerateStoriesByLevelAsync(
        string topic,
        IDictionary<string, IReadOnlyList<string>> vocabularyByLevel,
        IDictionary<string, int>? lengthByLevel = null,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Generating stories for multiple levels: Topic={Topic}, LevelCount={Count}",
            topic, vocabularyByLevel?.Count ?? 0);

        var results = new Dictionary<string, string>();
        lengthByLevel ??= new Dictionary<string, int>();

        foreach (var kvp in vocabularyByLevel)
        {
            var level = kvp.Key;
            var vocabulary = kvp.Value;
            var length = lengthByLevel.TryGetValue(level, out var l) ? l : 200;

            try
            {
                var story = await GenerateStoryAsync(
                    level,
                    topic,
                    vocabulary,
                    length,
                    cancellationToken);

                results[level] = story;
                _logger.LogInformation("Generated story for level: {Level}", level);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to generate story for level {Level}", level);
                results[level] = string.Empty;
            }
        }

        return results;
    }

    /// <summary>
    /// Validates the generated story meets basic requirements.
    /// </summary>
    /// <param name="story">The generated story text</param>
    /// <param name="level">The target CEFR level</param>
    /// <param name="vocabularyWords">The vocabulary words that should be included</param>
    /// <exception cref="InvalidOperationException">Thrown when story validation fails</exception>
    private void ValidateStory(
        string story,
        string level,
        IReadOnlyList<string>? vocabularyWords)
    {
        if (string.IsNullOrWhiteSpace(story))
        {
            _logger.LogError("Generated story is empty");
            throw new InvalidOperationException("Generated story is empty");
        }

        // Check minimum length based on level
        var minLength = GetMinStoryLength(level);
        if (story.Length < minLength)
        {
            _logger.LogWarning(
                "Generated story is too short: {Length} characters (min: {Min})",
                story.Length, minLength);
            // Don't throw - just log warning, AI might generate short stories
        }

        // Check if vocabulary words are included (if provided)
        if (vocabularyWords != null && vocabularyWords.Count > 0)
        {
            var storyLower = story.ToLower();
            var missingWords = vocabularyWords
                .Where(w => !string.IsNullOrWhiteSpace(w))
                .Where(w => !storyLower.Contains(w.ToLower()))
                .ToList();

            if (missingWords.Count > vocabularyWords.Count * 0.5)
            {
                _logger.LogWarning(
                    "Many vocabulary words missing from story: {MissingCount}/{TotalCount}",
                    missingWords.Count, vocabularyWords.Count);
            }
        }
    }

    /// <summary>
    /// Gets the minimum expected story length based on CEFR level.
    /// </summary>
    /// <param name="level">The CEFR level</param>
    /// <returns>Minimum character count</returns>
    private int GetMinStoryLength(string level)
    {
        return level.ToUpper() switch
        {
            "A1" => 100,
            "A2" => 150,
            "B1" => 200,
            "B2" => 300,
            "C1" => 400,
            _ => 100
        };
    }

    /// <summary>
    /// Tests the story generation service.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>True if service is working, false otherwise</returns>
    public virtual async Task<bool> TestServiceAsync(CancellationToken cancellationToken = default)
    {
        try
        {
            // Generate a simple test story
            var story = await GenerateStoryAsync(
                "A1",
                "Test",
                new List<string> { "Hallo", "Welt" },
                50,
                cancellationToken);

            return !string.IsNullOrWhiteSpace(story);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Story generation service test failed");
            return false;
        }
    }
}