Musify/backend/Core/Musify.Infrastructure/Services/AudioTranscoderService.cs

using System.Diagnostics;
using System.Globalization;
using System.Text.RegularExpressions;
using Microsoft.Extensions.Logging;
using Musify.Application.Contracts;
using Musify.Infrastructure.Configuration;

namespace Musify.Infrastructure.Services;

public partial class AudioService(ILogger<AudioService> logger,
    AudioConfiguration audioConfiguration)
    : IAudioTranscoderService
{
    private record FfmpegExecutionResult(int ExitCode, string StandardOutput, string StandardError);

    [GeneratedRegex(@"Duration:\s*(\d+):(\d{2}):(\d{2}(?:\.\d+)?)", RegexOptions.IgnoreCase)]
    private static partial Regex DurationRegex();

    public async Task<AudioTranscodeResult> TranscodeToAudioFileAsync(Stream audioStream, string destinationPath, CancellationToken cancellationToken)
    {
        try
        {
            Directory.CreateDirectory(destinationPath);

            logger.LogInformation("Starting audio transcoding for {DestinationPath}", destinationPath);

            var executionResult = await ExecuteFfmpegWithInputAsync(
                BuildAudioFileArguments(destinationPath, audioConfiguration.Ffmpeg),
                destinationPath,
                audioStream,
                "TranscodeToAudioFile",
                cancellationToken);

            if (executionResult.ExitCode != 0)
            {
                logger.LogError("Audio transcoding failed with exit code {ExitCode}. Output: {StandardOutput}, Error: {StandardError}",
                    executionResult.ExitCode, executionResult.StandardOutput, executionResult.StandardError);
                return new AudioTranscodeResult(executionResult.ExitCode, TimeSpan.Zero);
            }

            logger.LogInformation("Audio transcoding completed for {DestinationPath}", destinationPath);

            var outputPath = Path.Combine(destinationPath, audioConfiguration.Ffmpeg.OutputFileName);
            var duration = await GetAudioDurationAsync(outputPath, cancellationToken);
            return new AudioTranscodeResult(executionResult.ExitCode, duration);
        }
        catch (TimeoutException timeoutException)
        {
            logger.LogError(timeoutException, "Audio transcoding timed out after {Timeout} for {DestinationPath}", audioConfiguration.TranscodingTimeout, destinationPath);
            throw;
        }
        catch (Exception exception)
        {
            logger.LogError(exception, "Failed to transcode audio for {DestinationPath}", destinationPath);
            throw;
        }
    }

    private async Task<TimeSpan> GetAudioDurationAsync(string filePath, CancellationToken cancellationToken)
    {
        var executionResult = await ExecuteFfmpegAsync(
            BuildProbeDurationArguments(filePath),
            Path.GetDirectoryName(filePath) ?? Environment.CurrentDirectory,
            "ProbeAudioDuration",
            cancellationToken);

        var match = DurationRegex().Match(executionResult.StandardError);
        if (!match.Success)
            throw new InvalidOperationException($"Could not determine audio duration for {filePath}.");

        var hours = int.Parse(match.Groups[1].Value, CultureInfo.InvariantCulture);
        var minutes = int.Parse(match.Groups[2].Value, CultureInfo.InvariantCulture);
        var seconds = double.Parse(match.Groups[3].Value, CultureInfo.InvariantCulture);

        return new TimeSpan(hours, minutes, 0) + TimeSpan.FromSeconds(seconds);
    }

    public async Task<bool> IsValidAudioFileAsync(string filePath, CancellationToken cancellationToken)
    {
        if (!File.Exists(filePath))
        {
            logger.LogWarning("Audio validation requested for non-existing file {FilePath}", filePath);
            return false;
        }

        try
        {
            logger.LogDebug("Validating audio file {FilePath}", filePath);

            var executionResult = await ExecuteFfmpegAsync(
                BuildValidateAudioArguments(filePath),
                Path.GetDirectoryName(filePath) ?? Environment.CurrentDirectory,
                "ValidateAudioFile",
                cancellationToken);

            var isValid = executionResult.ExitCode == 0;
            if (!isValid)
            {
                logger.LogWarning("Audio validation failed for {FilePath}: {StandardError}", filePath, executionResult.StandardError);
            }
            else
            {
                logger.LogDebug("Audio validation successful for {FilePath}", filePath);
            }

            return isValid;
        }
        catch (TimeoutException timeoutException)
        {
            logger.LogError(timeoutException, "Audio validation timed out for {FilePath}", filePath);
        }
        catch (Exception exception)
        {
            logger.LogError(exception, "Failed to validate audio file {FilePath}", filePath);
        }
        return false;
    }

    private async Task<FfmpegExecutionResult> ExecuteFfmpegWithInputAsync(
        string arguments,
        string workingDirectory,
        Stream inputStream,
        string operationName,
        CancellationToken cancellationToken)
    {
        using var process = BuildProcess(arguments, workingDirectory, redirectStandardInput: true);
        process.Start();

        logger.LogDebug("[{Operation}] ffmpeg started (PID: {ProcessId}) in {WorkingDirectory}", operationName, process.Id, workingDirectory);

        var outputTask = process.StandardOutput.ReadToEndAsync(cancellationToken);
        var errorTask = process.StandardError.ReadToEndAsync(cancellationToken);

        if (inputStream.CanSeek)
            inputStream.Position = 0;

        await inputStream.CopyToAsync(process.StandardInput.BaseStream, cancellationToken);
        process.StandardInput.Close();

        return await WaitForProcessResultAsync(process, outputTask, errorTask, operationName, cancellationToken);
    }

    private async Task<FfmpegExecutionResult> ExecuteFfmpegAsync(
        string arguments,
        string workingDirectory,
        string operationName,
        CancellationToken cancellationToken)
    {
        using var process = BuildProcess(arguments, workingDirectory, redirectStandardInput: false);
        process.Start();

        logger.LogDebug("[{Operation}] ffmpeg started (PID: {ProcessId}) in {WorkingDirectory}", operationName, process.Id, workingDirectory);

        var outputTask = process.StandardOutput.ReadToEndAsync(cancellationToken);
        var errorTask = process.StandardError.ReadToEndAsync(cancellationToken);

        return await WaitForProcessResultAsync(process, outputTask, errorTask, operationName, cancellationToken);
    }

    private Process BuildProcess(string arguments, string workingDirectory, bool redirectStandardInput)
        => new()
        {
            StartInfo = new ProcessStartInfo
            {
                FileName = audioConfiguration.Ffmpeg.ExecutableName,
                WorkingDirectory = workingDirectory,
                Arguments = arguments,
                RedirectStandardInput = redirectStandardInput,
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                UseShellExecute = false,
                CreateNoWindow = true,
            }
        };

    private async Task<FfmpegExecutionResult> WaitForProcessResultAsync(
        Process process,
        Task<string> outputTask,
        Task<string> errorTask,
        string operationName,
        CancellationToken cancellationToken)
    {
        using var linkedCancellationTokens = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        linkedCancellationTokens.CancelAfter(audioConfiguration.TranscodingTimeout);

        try
        {
            await process.WaitForExitAsync(linkedCancellationTokens.Token);
        }
        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
        {
            logger.LogError("[{Operation}] ffmpeg timed out after {Timeout} (PID: {ProcessId})",
                operationName, audioConfiguration.TranscodingTimeout, process.Id);

            TryKillProcess(process);
            throw new TimeoutException($"ffmpeg execution exceeded timeout {audioConfiguration.TranscodingTimeout}.");
        }

        var standardError = await errorTask;
        var standardOutput = await outputTask;

        logger.LogDebug("[{Operation}] ffmpeg finished (PID: {ProcessId}). Exit code: {ExitCode}, Output: {OutputLength}B, Error: {ErrorLength}B",
            operationName, process.Id, process.ExitCode, standardOutput.Length, standardError.Length);

        return new FfmpegExecutionResult(process.ExitCode, standardOutput, standardError);
    }

    private void TryKillProcess(Process process)
    {
        try
        {
            if (!process.HasExited)
                process.Kill();
        }
        catch (Exception exception)
        {
            logger.LogError(exception, "Failed to kill ffmpeg process (PID: {ProcessId})", process.Id);
        }
    }

    private static string BuildAudioFileArguments(string outputDirectory, FfmpegConfiguration ffmpegConfiguration)
    {
        var outputPath = Path.Combine(outputDirectory, ffmpegConfiguration.OutputFileName);
        var additionalArguments = string.IsNullOrWhiteSpace(ffmpegConfiguration.AdditionalArguments)
            ? string.Empty
            : $" {ffmpegConfiguration.AdditionalArguments.Trim()}";

        return "-y -hide_banner -loglevel error " +
               "-i pipe:0 " +
               "-vn " +
               "-map 0:a " +
               $"-c:a {ffmpegConfiguration.AudioCodec} " +
               $"-b:a {ffmpegConfiguration.AudioBitrate} " +
               $"-ac {ffmpegConfiguration.AudioChannels} " +
               $"-ar {ffmpegConfiguration.AudioSampleRate} " +
               $"-profile:a {ffmpegConfiguration.AudioProfile} " +
               "-movflags +faststart" +
               additionalArguments +
               $" \"{outputPath}\"";
    }

    private static string BuildValidateAudioArguments(string filePath)
        => $"-v error -i \"{filePath}\" -map 0:a:0 -f null -";

    private static string BuildProbeDurationArguments(string filePath)
        => $"-hide_banner -i \"{filePath}\" -f null -";
}