DeutschLernen/GermanApp/Application/Services/SpeechExerciseService.cs

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

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for managing speech exercises using Vosk speech recognition.
/// This is part of the Application layer.
/// </summary>
public class SpeechExerciseService
{
    private readonly IVoskService _voskService;
    private readonly ILogger<SpeechExerciseService> _logger;

    /// <summary>
    /// Creates a new SpeechExerciseService.
    /// </summary>
    /// <param name="voskService">The Vosk speech recognition service</param>
    /// <param name="logger">Logger for service operations</param>
    public SpeechExerciseService(
        IVoskService voskService,
        ILogger<SpeechExerciseService> logger)
    {
        _voskService = voskService;
        _logger = logger;
    }

    /// <summary>
    /// Recognizes speech from audio bytes and returns the transcribed text.
    /// </summary>
    /// <param name="audioBytes">The audio data in bytes</param>
    /// <param name="expectedText">Optional expected text for verification</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Result containing recognized text and accuracy</returns>
    public virtual async Task<SpeechRecognitionResult> RecognizeSpeechAsync(
        byte[] audioBytes,
        string? expectedText = null,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Recognizing speech from audio: {ByteCount} bytes", audioBytes?.Length ?? 0);

        try
        {
            var recognizedText = await _voskService.RecognizeSpeechAsync(
                audioBytes,
                _voskService.GetType().Name == "VoskService" ? 16000 : 16000,
                null,
                cancellationToken);

            // Calculate accuracy if expected text is provided
            var accuracy = expectedText != null
                ? CalculateAccuracy(recognizedText, expectedText)
                : 0.0;

            _logger.LogInformation(
                "Speech recognized: Text={Text}, Accuracy={Accuracy:P0}",
                recognizedText, accuracy);

            return new SpeechRecognitionResult
            {
                RecognizedText = recognizedText,
                ExpectedText = expectedText,
                Accuracy = accuracy,
                IsCorrect = accuracy >= 0.8
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to recognize speech");
            throw new AiServiceException(
                "Failed to recognize speech: " + ex.Message,
                AiErrorCode.Temporary);
        }
    }

    /// <summary>
    /// Recognizes speech from an audio file.
    /// </summary>
    /// <param name="audioFilePath">Path to the audio file</param>
    /// <param name="expectedText">Optional expected text for verification</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Result containing recognized text and accuracy</returns>
    public virtual async Task<SpeechRecognitionResult> RecognizeSpeechFromFileAsync(
        string audioFilePath,
        string? expectedText = null,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Recognizing speech from file: {FilePath}", audioFilePath);

        try
        {
            var recognizedText = await _voskService.RecognizeSpeechFromFileAsync(
                audioFilePath,
                cancellationToken);

            var accuracy = expectedText != null
                ? CalculateAccuracy(recognizedText, expectedText)
                : 0.0;

            return new SpeechRecognitionResult
            {
                RecognizedText = recognizedText,
                ExpectedText = expectedText,
                Accuracy = accuracy,
                IsCorrect = accuracy >= 0.8
            };
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to recognize speech from file");
            throw;
        }
    }

    /// <summary>
    /// Verifies if spoken audio matches expected text.
    /// </summary>
    /// <param name="audioBytes">The audio data in bytes</param>
    /// <param name="expectedText">The expected text</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Result with accuracy and correctness</returns>
    public virtual async Task<SpeechRecognitionResult> VerifySpeechAsync(
        byte[] audioBytes,
        string expectedText,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Verifying speech: Expected={Expected}", expectedText);

        var result = await RecognizeSpeechAsync(audioBytes, expectedText, cancellationToken);
        
        // Additional validation for speech exercises
        result.PronunciationScore = CalculatePronunciationScore(result.RecognizedText, expectedText);
        result.FluencyScore = CalculateFluencyScore(audioBytes);

        return result;
    }

    /// <summary>
    /// Creates a speech exercise for practicing a specific phrase.
    /// </summary>
    /// <param name="phrase">The phrase to practice</param>
    /// <param name="difficulty">Exercise difficulty level</param>
    /// <param name="hints">Optional pronunciation hints</param>
    /// <returns>Speech exercise with metadata</returns>
    public virtual SpeechExercise CreateExercise(
        string phrase,
        string difficulty = "medium",
        IReadOnlyList<string>? hints = null)
    {
        _logger.LogInformation("Creating speech exercise: Phrase={Phrase}, Difficulty={Difficulty}", phrase, difficulty);

        return new SpeechExercise
        {
            Id = Guid.NewGuid().ToString(),
            Phrase = phrase,
            Difficulty = difficulty,
            Hints = hints ?? new List<string>(),
            CreatedAt = DateTime.UtcNow
        };
    }

    /// <summary>
    /// Evaluates a user's attempt at a speech exercise.
    /// </summary>
    /// <param name="exerciseId">The exercise ID</param>
    /// <param name="audioBytes">The user's audio attempt</param>
    /// <param name="expectedPhrase">The expected phrase (from exercise)</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Evaluation result with scores</returns>
    public virtual async Task<SpeechExerciseEvaluation> EvaluateExerciseAttemptAsync(
        string exerciseId,
        byte[] audioBytes,
        string expectedPhrase,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Evaluating exercise attempt: ExerciseId={ExerciseId}", exerciseId);

        var result = await VerifySpeechAsync(audioBytes, expectedPhrase, cancellationToken);

        return new SpeechExerciseEvaluation
        {
            ExerciseId = exerciseId,
            ExpectedPhrase = expectedPhrase,
            RecognizedText = result.RecognizedText,
            Accuracy = result.Accuracy,
            PronunciationScore = result.PronunciationScore,
            FluencyScore = result.FluencyScore,
            IsPassed = result.IsCorrect && result.Accuracy >= 0.8,
            AttemptedAt = DateTime.UtcNow
        };
    }

    /// <summary>
    /// Tests the speech exercise 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
        {
            // We can't test without actual audio, so just verify the service is initialized
            var modelInfo = await _voskService.GetModelInfoAsync();
            return modelInfo.ModelName != null;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Speech exercise service test failed");
            return false;
        }
    }

    /// <summary>
    /// Calculates text matching accuracy between recognized and expected text.
    /// </summary>
    /// <param name="recognized">The recognized text</param>
    /// <param name="expected">The expected text</param>
    /// <returns>Accuracy score (0.0 to 1.0)</returns>
    private double CalculateAccuracy(string recognized, string expected)
    {
        if (string.IsNullOrWhiteSpace(expected))
            return 1.0;

        if (string.IsNullOrWhiteSpace(recognized))
            return 0.0;

        // Normalize both strings
        var recognizedNormalized = recognized.Trim().ToLower();
        var expectedNormalized = expected.Trim().ToLower();

        // Simple exact match
        if (recognizedNormalized == expectedNormalized)
            return 1.0;

        // Calculate Levenshtein distance for similarity
        var distance = LevenshteinDistance(recognizedNormalized, expectedNormalized);
        var maxLength = Math.Max(recognizedNormalized.Length, expectedNormalized.Length);
        
        if (maxLength == 0)
            return 1.0;

        var similarity = 1.0 - (distance / (double)maxLength);
        return Math.Max(0.0, Math.Min(1.0, similarity));
    }

    /// <summary>
    /// Calculates pronunciation score based on text matching.
    /// </summary>
    private double CalculatePronunciationScore(string recognized, string expected)
    {
        // For now, use accuracy as pronunciation score
        // In a real implementation, you might use audio analysis
        return CalculateAccuracy(recognized, expected);
    }

    /// <summary>
    /// Calculates fluency score based on audio characteristics.
    /// </summary>
    private double CalculateFluencyScore(byte[] audioBytes)
    {
        // Simple heuristic: longer audio with consistent speaking rate
        // In a real implementation, analyze audio features
        if (audioBytes == null || audioBytes.Length == 0)
            return 0.0;

        // Assume 16kHz sample rate, 2 bytes per sample (16-bit)
        var durationSeconds = audioBytes.Length / (16000.0 * 2);
        
        // Give higher score for longer, consistent speech
        if (durationSeconds >= 3.0)
            return 1.0;
        if (durationSeconds >= 1.5)
            return 0.8;
        if (durationSeconds >= 0.5)
            return 0.6;
        
        return 0.4;
    }

    /// <summary>
    /// Calculates Levenshtein distance between two strings.
    /// </summary>
    private static int LevenshteinDistance(string s, string t)
    {
        if (string.IsNullOrEmpty(s))
        {
            return string.IsNullOrEmpty(t) ? 0 : t.Length;
        }
        if (string.IsNullOrEmpty(t))
        {
            return s.Length;
        }

        var n = s.Length;
        var m = t.Length;
        var d = new int[n + 1, m + 1];

        for (int i = 0; i <= n; d[i, 0] = i++)
            ;
        for (int j = 1; j <= m; d[0, j] = j++)
            ;

        for (int i = 1; i <= n; i++)
        {
            for (int j = 1; j <= m; j++)
            {
                var cost = (t[j - 1] == s[i - 1]) ? 0 : 1;
                d[i, j] = Math.Min(
                    Math.Min(d[i - 1, j] + 1, d[i, j - 1] + 1),
                    d[i - 1, j - 1] + cost);
            }
        }
        return d[n, m];
    }
}

/// <summary>
/// Result of speech recognition.
/// </summary>
public class SpeechRecognitionResult
{
    /// <summary>
    /// The recognized text.
    /// </summary>
    public string RecognizedText { get; set; } = string.Empty;

    /// <summary>
    /// The expected text (if provided for verification).
    /// </summary>
    public string? ExpectedText { get; set; }

    /// <summary>
    /// Accuracy score (0.0 to 1.0).
    /// </summary>
    public double Accuracy { get; set; }

    /// <summary>
    /// Pronunciation score (0.0 to 1.0).
    /// </summary>
    public double PronunciationScore { get; set; }

    /// <summary>
    /// Fluency score (0.0 to 1.0).
    /// </summary>
    public double FluencyScore { get; set; }

    /// <summary>
    /// Whether the recognition is considered correct.
    /// </summary>
    public bool IsCorrect { get; set; }
}

/// <summary>
/// Represents a speech exercise.
/// </summary>
public class SpeechExercise
{
    /// <summary>
    /// Unique identifier for the exercise.
    /// </summary>
    public string Id { get; set; } = string.Empty;

    /// <summary>
    /// The phrase to practice.
    /// </summary>
    public string Phrase { get; set; } = string.Empty;

    /// <summary>
    /// Difficulty level (easy, medium, hard).
    /// </summary>
    public string Difficulty { get; set; } = "medium";

    /// <summary>
    /// Pronunciation hints.
    /// </summary>
    public IReadOnlyList<string> Hints { get; set; } = new List<string>();

    /// <summary>
    /// When the exercise was created.
    /// </summary>
    public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
}

/// <summary>
/// Result of evaluating a speech exercise attempt.
/// </summary>
public class SpeechExerciseEvaluation
{
    /// <summary>
    /// The exercise ID.
    /// </summary>
    public string ExerciseId { get; set; } = string.Empty;

    /// <summary>
    /// The expected phrase.
    /// </summary>
    public string ExpectedPhrase { get; set; } = string.Empty;

    /// <summary>
    /// The recognized text.
    /// </summary>
    public string RecognizedText { get; set; } = string.Empty;

    /// <summary>
    /// Accuracy score (0.0 to 1.0).
    /// </summary>
    public double Accuracy { get; set; }

    /// <summary>
    /// Pronunciation score (0.0 to 1.0).
    /// </summary>
    public double PronunciationScore { get; set; }

    /// <summary>
    /// Fluency score (0.0 to 1.0).
    /// </summary>
    public double FluencyScore { get; set; }

    /// <summary>
    /// Whether the attempt passed.
    /// </summary>
    public bool IsPassed { get; set; }

    /// <summary>
    /// When the attempt was made.
    /// </summary>
    public DateTime AttemptedAt { get; set; } = DateTime.UtcNow;
}