DeutschLernen/GermanApp/Application/Services/AiFallbackService.cs

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

namespace GermanApp.Application.Services;

/// <summary>
/// Service for handling AI service failures and providing fallback responses.
/// This is part of the Application layer.
/// </summary>
public class AiFallbackService
{
    private readonly IMistralService? _mistralService;
    private readonly IVoskService? _voskService;
    private readonly ITtsService? _ttsService;
    private readonly ILogger<AiFallbackService> _logger;

    /// <summary>
    /// Creates a new AiFallbackService.
    /// </summary>
    /// <param name="mistralService">The Mistral text generation service (optional)</param>
    /// <param name="voskService">The Vosk speech recognition service (optional)</param>
    /// <param name="ttsService">The Coqui TTS service (optional)</param>
    /// <param name="logger">Logger for service operations</param>
    public AiFallbackService(
        IMistralService? mistralService,
        IVoskService? voskService,
        ITtsService? ttsService,
        ILogger<AiFallbackService> logger)
    {
        _mistralService = mistralService;
        _voskService = voskService;
        _ttsService = ttsService;
        _logger = logger;
    }

    /// <summary>
    /// Attempts to generate a story, with fallback if the primary service fails.
    /// </summary>
    /// <param name="level">The CEFR level</param>
    /// <param name="topic">The story topic</param>
    /// <param name="vocabularyWords">List of vocabulary words</param>
    /// <param name="length">Approximate word count</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Generated story text, or fallback if AI service fails</returns>
    public virtual async Task<string> GenerateStoryWithFallbackAsync(
        string level,
        string topic,
        IReadOnlyList<string> vocabularyWords,
        int length = 200,
        CancellationToken cancellationToken = default)
    {
        try
        {
            if (_mistralService != null)
            {
                return await _mistralService.GenerateStoryAsync(
                    level,
                    topic,
                    vocabularyWords,
                    length,
                    cancellationToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Mistral story generation failed, using fallback");
        }

        // Fallback: Generate a simple story based on parameters
        return GenerateFallbackStory(level, topic, vocabularyWords, length);
    }

    /// <summary>
    /// Attempts to provide writing feedback, with fallback if the primary service fails.
    /// </summary>
    /// <param name="userText">The user's text</param>
    /// <param name="level">The CEFR level</param>
    /// <param name="customPrompt">Optional custom prompt</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Feedback text, or fallback if AI service fails</returns>
    public virtual async Task<string> ProvideFeedbackWithFallbackAsync(
        string userText,
        string level,
        string? customPrompt = null,
        CancellationToken cancellationToken = default)
    {
        try
        {
            if (_mistralService != null)
            {
                return await _mistralService.GenerateWritingFeedbackAsync(
                    userText,
                    level,
                    customPrompt,
                    cancellationToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Mistral feedback generation failed, using fallback");
        }

        // Fallback: Provide simple feedback based on text length
        return GenerateFallbackFeedback(userText, level);
    }

    /// <summary>
    /// Attempts to recognize speech, with fallback if the primary service fails.
    /// </summary>
    /// <param name="audioBytes">The audio data</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Recognized text, or empty string if service fails</returns>
    public virtual async Task<string> RecognizeSpeechWithFallbackAsync(
        byte[] audioBytes,
        CancellationToken cancellationToken = default)
    {
        try
        {
            if (_voskService != null)
            {
                return await _voskService.RecognizeSpeechAsync(
                    audioBytes,
                    16000,
                    null,
                    cancellationToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Vosk speech recognition failed, using fallback");
        }

        // Fallback: Return empty string or transcription placeholder
        return "[Speech transcription unavailable - please try again]";
    }

    /// <summary>
    /// Attempts to generate audio, with fallback if the primary service fails.
    /// </summary>
    /// <param name="text">The text to convert to speech</param>
    /// <param name="language">The language code</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Audio data, or empty array if service fails</returns>
    public virtual async Task<byte[]> GenerateAudioWithFallbackAsync(
        string text,
        string language = "de",
        CancellationToken cancellationToken = default)
    {
        try
        {
            if (_ttsService != null)
            {
                return await _ttsService.GenerateAudioAsync(
                    text,
                    null,
                    language,
                    cancellationToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "TTS audio generation failed, using fallback");
        }

        // Fallback: Return empty audio array
        return new byte[0];
    }

    /// <summary>
    /// Checks if AI services are healthy.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Dictionary mapping service names to health status</returns>
    public virtual async Task<IDictionary<string, bool>> CheckServiceHealthAsync(
        CancellationToken cancellationToken = default)
    {
        var health = new Dictionary<string, bool>();

        // Check Mistral service
        if (_mistralService != null)
        {
            try
            {
                var isHealthy = await _mistralService.TestConnectionAsync(cancellationToken);
                health["Mistral"] = isHealthy;
            }
            catch
            {
                health["Mistral"] = false;
            }
        }
        else
        {
            health["Mistral"] = false;
        }

        // Check Vosk service
        if (_voskService != null)
        {
            try
            {
                var isHealthy = await _voskService.TestModelAsync(cancellationToken);
                health["Vosk"] = isHealthy;
            }
            catch
            {
                health["Vosk"] = false;
            }
        }
        else
        {
            health["Vosk"] = false;
        }

        // Check Coqui TTS service
        if (_ttsService != null)
        {
            try
            {
                var isHealthy = await _ttsService.TestModelAsync(cancellationToken);
                health["CoquiTTS"] = isHealthy;
            }
            catch
            {
                health["CoquiTTS"] = false;
            }
        }
        else
        {
            health["CoquiTTS"] = false;
        }

        return health;
    }

    /// <summary>
    /// Gets a human-readable status message for AI services.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Status message describing which services are available</returns>
    public virtual async Task<string> GetServiceStatusMessageAsync(
        CancellationToken cancellationToken = default)
    {
        var health = await CheckServiceHealthAsync(cancellationToken);
        var available = health.Where(kvp => kvp.Value).Select(kvp => kvp.Key).ToList();
        var unavailable = health.Where(kvp => !kvp.Value).Select(kvp => kvp.Key).ToList();

        var message = "AI Service Status: ";

        if (available.Count > 0)
        {
            message += "Available: ";
            message += string.Join(", ", available);
        }

        if (unavailable.Count > 0)
        {
            if (available.Count > 0)
                message += "; ";
            message += "Unavailable: ";
            message += string.Join(", ", unavailable);
        }

        return message;
    }

    /// <summary>
    /// Generates a fallback story when AI service is unavailable.
    /// </summary>
    private string GenerateFallbackStory(
        string level,
        string topic,
        IReadOnlyList<string> vocabularyWords,
        int length)
    {
        _logger.LogInformation("Generating fallback story for: Level={Level}, Topic={Topic}", level, topic);

        // Create a simple story based on the topic and vocabulary
        var story = $"Ein {GetLevelDescription(level)} Story über {topic}.";

        if (vocabularyWords != null && vocabularyWords.Count > 0)
        {
            story += " Es enthält die Wörter: " + string.Join(", ", vocabularyWords.Take(5));
        }

        // Add some generic story content based on topic
        story += " " + GetGenericStoryContent(topic, length);

        return story;
    }

    /// <summary>
    /// Generates fallback feedback when AI service is unavailable.
    /// </summary>
    private string GenerateFallbackFeedback(string userText, string level)
    {
        _logger.LogInformation("Generating fallback feedback for: Level={Level}", level);

        var feedback = $"Feedback for {level} level: ";

        // Simple length-based feedback
        if (string.IsNullOrWhiteSpace(userText))
        {
            feedback += "Please write some text to receive feedback.";
        }
        else if (userText.Length < 20)
        {
            feedback += "Your text is quite short. Try writing a few more sentences.";
        }
        else if (userText.Length < 100)
        {
            feedback += "Good start! Your text is clear. Keep practicing to improve.";
        }
        else
        {
            feedback += "Great job! Your text is well-developed. Continue practicing to maintain your skills.";
        }

        return feedback;
    }

    /// <summary>
    /// Gets a description for the CEFR level.
    /// </summary>
    private string GetLevelDescription(string level)
    {
        return level.ToUpper() switch
        {
            "A1" => "einfacher",
            "A2" => "leichter",
            "B1" => "mittelschwerer",
            "B2" => "fortgeschrittener",
            "C1" => "komplexer",
            _ => "einfacher"
        };
    }

    /// <summary>
    /// Gets generic story content based on topic.
    /// </summary>
    private string GetGenericStoryContent(string topic, int length)
    {
        // Simple topic-based content
        var topics = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase)
        {
            ["food"] = "Es geht um Essen und Trinken.",
            ["travel"] = "Es geht um Reisen und Abenteuer.",
            ["family"] = "Es geht um Familie und Beziehungen.",
            ["work"] = "Es geht um Arbeit und Beruf.",
            ["school"] = "Es geht um Schule und Lernen.",
            ["animals"] = "Es geht um Tiere und Natur.",
            ["sports"] = "Es geht um Sport und Bewegung.",
            ["holiday"] = "Es geht um Ferien und Feiertage.",
            ["weather"] = "Es geht um das Wetter.",
            ["shopping"] = "Es geht um Einkaufen."
        };

        if (topics.TryGetValue(topic, out var content))
        {
            return content;
        }

        return "Es geht um ein interessantes Thema.";
    }

    /// <summary>
    /// Tests the fallback service.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>True if service is working</returns>
    public virtual async Task<bool> TestServiceAsync(CancellationToken cancellationToken = default)
    {
        try
        {
            // Test fallback story generation
            var story = GenerateFallbackStory("A1", "Test", new List<string> { "Test" }, 100);
            if (string.IsNullOrWhiteSpace(story))
                return false;

            // Test fallback feedback generation
            var feedback = GenerateFallbackFeedback("Test", "A1");
            if (string.IsNullOrWhiteSpace(feedback))
                return false;

            // Test health check
            var health = await CheckServiceHealthAsync(cancellationToken);
            return health.Count > 0;
        }
        catch
        {
            return false;
        }
    }
}