DeutschLernen/GermanApp/Infrastructure/Services/VoskService.cs

using GermanApp.Domain.Interfaces;
using GermanApp.Infrastructure.Configuration;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using System.Diagnostics;
using System.Text;
using System.Text.Json;

namespace GermanApp.Infrastructure.Services;

/// <summary>
/// Infrastructure service for Vosk speech recognition.
/// Uses Python process to call Vosk library.
/// This is part of the Infrastructure layer.
/// </summary>
public class VoskService : IVoskService
{
    private readonly VoskConfig _config;
    private readonly ILogger<VoskService> _logger;

    public VoskService(
        IOptions<VoskConfig> config,
        ILogger<VoskService> logger)
    {
        _config = config.Value;
        _logger = logger;
        
        // Validate model path on startup
        ValidateModelPath();
    }

    /// <summary>
    /// Validates that the Vosk model directory exists and is accessible.
    /// </summary>
    /// <exception cref="InvalidOperationException">Thrown when model path is not configured</exception>
    /// <exception cref="DirectoryNotFoundException">Thrown when model directory doesn't exist</exception>
    private void ValidateModelPath()
    {
        if (string.IsNullOrWhiteSpace(_config.ModelPath))
        {
            _logger.LogError("Vosk ModelPath is not configured. Please set Vosk:ModelPath in appsettings.json");
            throw new InvalidOperationException(
                "Vosk model path is not configured. " +
                "Please download vosk-model-de-0.22 from https://alphacephei.com/vosk/models " +
                "and set the ModelPath in appsettings.json");
        }

        if (!Directory.Exists(_config.ModelPath))
        {
            _logger.LogError("Vosk model directory not found: {ModelPath}", _config.ModelPath);
            throw new DirectoryNotFoundException(
                $"Vosk model directory not found: {_config.ModelPath}. " +
                "Please download vosk-model-de-0.22 from https://alphacephei.com/vosk/models " +
                "and extract it to the configured path");
        }
        
        _logger.LogInformation("Vosk model directory validated: {ModelPath}", _config.ModelPath);
    }

    /// <summary>
    /// Recognizes speech from audio bytes.
    /// </summary>
    public virtual async Task<string> RecognizeSpeechAsync(
        byte[] audioBytes,
        int sampleRate = 16000,
        string? hint = null,
        CancellationToken cancellationToken = default)
    {
        if (audioBytes == null || audioBytes.Length == 0)
            throw new ArgumentException("Audio data cannot be empty", nameof(audioBytes));

        // Validate sample rate
        if (sampleRate != _config.SampleRate)
        {
            _logger.LogWarning(
                "Audio sample rate ({SampleRate}) does not match expected ({Expected}). " +
                "Results may be inaccurate.",
                sampleRate,
                _config.SampleRate);
        }

        // Write audio to temp file
        var tempFile = Path.GetTempFileName() + ".wav";
        try
        {
            await File.WriteAllBytesAsync(tempFile, audioBytes, cancellationToken);
            
            return await RecognizeFromFileInternalAsync(tempFile, hint, cancellationToken);
        }
        finally
        {
            // Clean up temp file
            try { File.Delete(tempFile); }
            catch (Exception ex) { _logger.LogError(ex, "Failed to delete temp file: {File}", tempFile); }
        }
    }

    /// <summary>
    /// Recognizes speech from an audio file path.
    /// </summary>
    public virtual async Task<string> RecognizeSpeechFromFileAsync(
        string audioFilePath,
        CancellationToken cancellationToken = default)
    {
        if (!File.Exists(audioFilePath))
            throw new FileNotFoundException("Audio file not found", audioFilePath);

        return await RecognizeFromFileInternalAsync(audioFilePath, null, cancellationToken);
    }

    /// <summary>
    /// Recognizes speech from a stream.
    /// </summary>
    public virtual async Task<string> RecognizeSpeechFromStreamAsync(
        System.IO.Stream audioStream,
        int sampleRate = 16000,
        CancellationToken cancellationToken = default)
    {
        if (audioStream == null || !audioStream.CanRead)
            throw new ArgumentException("Audio stream must be readable", nameof(audioStream));

        // Read stream to temp file
        var tempFile = Path.GetTempFileName() + ".wav";
        try
        {
            using (var fileStream = File.Create(tempFile))
            {
                await audioStream.CopyToAsync(fileStream, cancellationToken);
            }
            
            return await RecognizeFromFileInternalAsync(tempFile, null, cancellationToken);
        }
        finally
        {
            try { File.Delete(tempFile); }
            catch (Exception ex) { _logger.LogError(ex, "Failed to delete temp file: {File}", tempFile); }
        }
    }

    /// <summary>
    /// Internal method to recognize from file with error handling.
    /// </summary>
    private async Task<string> RecognizeFromFileInternalAsync(
        string audioFilePath,
        string? hint,
        CancellationToken cancellationToken)
    {
        // Validate model path
        if (!Directory.Exists(_config.ModelPath))
            throw new InvalidOperationException(
                $"Vosk model directory not found: {_config.ModelPath}");

        // Build Python command
        var script = BuildRecognitionScript(audioFilePath, hint);
        var tempScript = Path.GetTempFileName() + ".py";
        
        try
        {
            // Write the Python script to a temp file
            await File.WriteAllTextAsync(tempScript, script, cancellationToken);
            
            // Execute Python process
            var result = await ExecutePythonProcessAsync(tempScript, cancellationToken);
            
            // Parse result
            var recognizedText = ParseVoskOutput(result.StandardOutput);
            
            if (string.IsNullOrWhiteSpace(recognizedText))
            {
                _logger.LogWarning("Vosk returned empty result. stderr: {Error}", result.StandardError);
                throw new InvalidOperationException(
                    "Speech recognition failed: " + result.StandardError);
            }
            
            return recognizedText.Trim();
        }
        finally
        {
            try { File.Delete(tempScript); }
            catch (Exception ex) { _logger.LogError(ex, "Failed to delete temp script: {File}", tempScript); }
        }
    }

    /// <summary>
    /// Builds the Python script for speech recognition.
    /// </summary>
    private string BuildRecognitionScript(string audioFilePath, string? hint)
    {
        var script = new StringBuilder();
        script.AppendLine("import sys");
        script.AppendLine("import json");
        script.AppendLine();
        
        // Handle potential import errors
        script.AppendLine("try:");
        script.AppendLine("    from vosk import Model, KaldiRecognizer, SetLogLevel");
        script.AppendLine("except ImportError as e:");
        script.AppendLine("    print(json.dumps({'error': 'Vosk not installed: ' + str(e)}))");
        script.AppendLine("    sys.exit(1)");
        script.AppendLine();
        
        // Set log level to suppress warnings
        script.AppendLine("SetLogLevel(-1)");
        script.AppendLine();
        
        // Load model
        script.AppendLine($"model_path = '{_config.ModelPath.Replace("\\", "\\\\")}'");
        script.AppendLine("try:");
        script.AppendLine("    model = Model(model_path)");
        script.AppendLine("except Exception as e:");
        script.AppendLine("    print(json.dumps({'error': 'Failed to load model: ' + str(e)}))");
        script.AppendLine("    sys.exit(1)");
        script.AppendLine();
        
        // Configure recognizer
        script.AppendLine($"sample_rate = {_config.SampleRate}");
        script.AppendLine($"beam_width = {_config.BeamWidth}");
        script.AppendLine("rec = KaldiRecognizer(model, sample_rate)");
        if (!string.IsNullOrEmpty(hint))
        {
            script.AppendLine($"rec.SetGrammar('\"{hint.Replace("'", "\\'")}\"')");
        }
        script.AppendLine();
        
        // Process audio file
        script.AppendLine($"audio_path = '{audioFilePath.Replace("\\", "\\\\")}'");
        script.AppendLine("with open(audio_path, 'rb') as f:");
        script.AppendLine("    while True:");
        script.AppendLine("        data = f.read(4000)");
        script.AppendLine("        if len(data) == 0:");
        script.AppendLine("            break");
        script.AppendLine("        if rec.AcceptWaveform(data):");
        script.AppendLine("            pass");
        script.AppendLine("        else:");
        script.AppendLine("            pass");
        script.AppendLine();
        script.AppendLine("result = rec.FinalResult()");
        script.AppendLine("result_dict = json.loads(result)");
        script.AppendLine("print(result_dict.get('text', ''))");
        
        return script.ToString();
    }

    /// <summary>
    /// Executes a Python process and returns the result.
    /// </summary>
    private async Task<(string StandardOutput, string StandardError)> ExecutePythonProcessAsync(
        string scriptPath,
        CancellationToken cancellationToken)
    {
        var processInfo = new ProcessStartInfo
        {
            FileName = _config.PythonPath,
            Arguments = scriptPath,
            RedirectStandardOutput = true,
            RedirectStandardError = true,
            UseShellExecute = false,
            CreateNoWindow = true,
            StandardOutputEncoding = Encoding.UTF8,
            StandardErrorEncoding = Encoding.UTF8
        };

        using var process = new Process { StartInfo = processInfo };
        
        // Use a timeout for the process
        var timeoutTask = Task.Delay(_config.TimeoutSeconds * 1000, cancellationToken);
        
        process.Start();
        
        var outputTask = process.StandardOutput.ReadToEndAsync();
        var errorTask = process.StandardError.ReadToEndAsync();
        var exitTask = process.WaitForExitAsync(cancellationToken);
        
        // Wait for process to complete or timeout
        var completedTask = await Task.WhenAny(exitTask, timeoutTask);
        
        if (completedTask == timeoutTask)
        {
            // Kill the process if it times out
            try { process.Kill(); }
            catch { }
            
            _logger.LogError("Vosk process timed out after {Seconds} seconds", _config.TimeoutSeconds);
            throw new TimeoutException(
                $"Vosk speech recognition timed out after {_config.TimeoutSeconds} seconds");
        }
        
        var output = await outputTask;
        var error = await errorTask;
        
        return (output, error);
    }

    /// <summary>
    /// Parses Vosk JSON output to extract the recognized text.
    /// </summary>
    private string ParseVoskOutput(string output)
    {
        // Vosk outputs JSON with a "text" field
        try
        {
            using var doc = JsonDocument.Parse(output.Trim());
            if (doc.RootElement.TryGetProperty("text", out var textElement))
            {
                return textElement.GetString() ?? string.Empty;
            }
            // Sometimes the output is just the text directly
            return output.Trim();
        }
        catch
        {
            // If JSON parsing fails, try to return the output as-is
            return output.Trim();
        }
    }

    /// <summary>
    /// Tests the Vosk model and configuration.
    /// </summary>
    public virtual async Task<bool> TestModelAsync(CancellationToken cancellationToken = default)
    {
        try
        {
            // Create a simple test: try to recognize silence or a known phrase
            // For now, just validate that the model directory exists
            if (!Directory.Exists(_config.ModelPath))
                return false;
            
            // Try to run a simple test with an empty/short audio
            // This validates the Python environment and model loading
            var testAudio = new byte[100]; // Very short audio
            await RecognizeSpeechAsync(testAudio, _config.SampleRate, null, cancellationToken);
            
            return true;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Vosk model test failed");
            return false;
        }
    }

    /// <summary>
    /// Gets the current Vosk model information.
    /// </summary>
    public virtual Task<(string ModelName, string ModelPath)> GetModelInfoAsync()
    {
        var modelName = Path.GetFileName(_config.ModelPath.TrimEnd('/', '\\'));
        return Task.FromResult((modelName, _config.ModelPath));
    }
}