torrent-gateway/internal/transcoding/transcoder.go

package transcoding

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

// Quality represents a transcoding quality profile
type Quality struct {
	Name     string `json:"name"`
	Width    int    `json:"width"`
	Height   int    `json:"height"`
	Bitrate  string `json:"bitrate"`
	Preset   string `json:"preset"`
}

// Job represents a transcoding job
type Job struct {
	ID          string    `json:"id"`
	InputPath   string    `json:"input_path"`
	OutputDir   string    `json:"output_dir"`
	FileHash    string    `json:"file_hash"`
	Qualities   []Quality `json:"qualities"`
	Priority    int       `json:"priority"`
	Status      string    `json:"status"` // "queued", "processing", "completed", "failed"
	Progress    float64   `json:"progress"`
	Error       string    `json:"error,omitempty"`
	StartTime   time.Time `json:"start_time"`
	CompletedAt time.Time `json:"completed_at,omitempty"`
	Callback    func(error) `json:"-"`
}

// Transcoder handles video transcoding operations
type Transcoder struct {
	workDir     string
	ffmpegPath  string
	concurrent  int
	queue       chan Job
	jobs        map[string]*Job // Track job status
	enabled     bool
}

// DefaultQualities provides standard quality profiles
var DefaultQualities = []Quality{
	{Name: "1080p", Width: 1920, Height: 1080, Bitrate: "5000k", Preset: "fast"},
	{Name: "720p", Width: 1280, Height: 720, Bitrate: "2500k", Preset: "fast"},
	{Name: "480p", Width: 854, Height: 480, Bitrate: "1000k", Preset: "fast"},
}

// NewTranscoder creates a new transcoder instance
func NewTranscoder(workDir string, concurrent int, enabled bool) (*Transcoder, error) {
	if !enabled {
		return &Transcoder{
			enabled: false,
			jobs:    make(map[string]*Job),
		}, nil
	}

	// Verify FFmpeg is available
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return nil, fmt.Errorf("ffmpeg not found in PATH: %w", err)
	}

	// Create work directory if it doesn't exist
	if err := os.MkdirAll(workDir, 0755); err != nil {
		return nil, fmt.Errorf("failed to create work directory: %w", err)
	}

	t := &Transcoder{
		workDir:     workDir,
		ffmpegPath:  "ffmpeg",
		concurrent:  concurrent,
		queue:       make(chan Job, 100),
		jobs:        make(map[string]*Job),
		enabled:     true,
	}

	// Start worker goroutines
	for i := 0; i < concurrent; i++ {
		go t.worker()
	}

	return t, nil
}

// IsEnabled returns whether transcoding is enabled
func (t *Transcoder) IsEnabled() bool {
	return t.enabled
}

// worker processes jobs from the queue
func (t *Transcoder) worker() {
	for job := range t.queue {
		t.processJob(job)
	}
}

// SubmitJob adds a job to the transcoding queue
func (t *Transcoder) SubmitJob(job Job) {
	if !t.enabled {
		if job.Callback != nil {
			job.Callback(fmt.Errorf("transcoding is disabled"))
		}
		return
	}

	job.Status = "queued"
	job.StartTime = time.Now()
	t.jobs[job.ID] = &job
	t.queue <- job
}

// GetJobStatus returns the current status of a job
func (t *Transcoder) GetJobStatus(jobID string) (*Job, bool) {
	job, exists := t.jobs[jobID]
	return job, exists
}

// NeedsTranscoding checks if a file needs transcoding for web compatibility
func (t *Transcoder) NeedsTranscoding(filePath string) (bool, error) {
	if !t.enabled {
		return false, nil
	}

	// Use ffprobe to analyze the file
	cmd := exec.Command("ffprobe", "-v", "quiet", "-print_format", "json", "-show_format", "-show_streams", filePath)
	output, err := cmd.Output()
	if err != nil {
		return true, err // Assume needs transcoding if we can't analyze
	}

	outputStr := string(output)

	// Check if already in web-friendly format
	hasH264 := strings.Contains(outputStr, "\"codec_name\": \"h264\"")
	hasAAC := strings.Contains(outputStr, "\"codec_name\": \"aac\"")
	isMP4 := strings.HasSuffix(strings.ToLower(filePath), ".mp4")

	// If it's H.264/AAC in MP4 container, probably doesn't need transcoding
	if hasH264 && hasAAC && isMP4 {
		return false, nil
	}

	return true, nil
}

// CreateStreamingVersion creates a single web-compatible MP4 version
func (t *Transcoder) CreateStreamingVersion(inputPath, outputPath string) error {
	if !t.enabled {
		return fmt.Errorf("transcoding is disabled")
	}

	// Ensure output directory exists
	if err := os.MkdirAll(filepath.Dir(outputPath), 0755); err != nil {
		return fmt.Errorf("failed to create output directory: %w", err)
	}

	args := []string{
		"-i", inputPath,
		"-c:v", "libx264",      // H.264 video codec
		"-c:a", "aac",          // AAC audio codec  
		"-preset", "fast",      // Balance speed/quality
		"-crf", "23",           // Quality (23 is default, lower = better)
		"-maxrate", "2M",       // Max bitrate for streaming
		"-bufsize", "4M",       // Buffer size
		"-movflags", "+faststart", // Enable fast start for web
		"-y",                   // Overwrite output file
		outputPath,
	}

	cmd := exec.Command(t.ffmpegPath, args...)
	return cmd.Run()
}

// processJob handles the actual transcoding work
func (t *Transcoder) processJob(job Job) {
	job.Status = "processing"
	t.jobs[job.ID] = &job

	var err error
	defer func() {
		if err != nil {
			job.Status = "failed"
			job.Error = err.Error()
		} else {
			job.Status = "completed"
			job.Progress = 100.0
		}
		job.CompletedAt = time.Now()
		t.jobs[job.ID] = &job
		
		if job.Callback != nil {
			job.Callback(err)
		}
	}()

	// Create output directory
	if err = os.MkdirAll(job.OutputDir, 0755); err != nil {
		err = fmt.Errorf("failed to create output directory: %w", err)
		return
	}

	// Create streaming MP4 version (most important for web compatibility)
	outputPath := filepath.Join(job.OutputDir, "stream.mp4")
	err = t.CreateStreamingVersion(job.InputPath, outputPath)
	if err != nil {
		err = fmt.Errorf("transcoding failed: %w", err)
		return
	}

	job.Progress = 100.0
}

// GetTranscodedPath returns the path to a transcoded file if it exists
func (t *Transcoder) GetTranscodedPath(fileHash string) string {
	if !t.enabled {
		return ""
	}

	streamPath := filepath.Join(t.workDir, fileHash, "stream.mp4")
	if _, err := os.Stat(streamPath); err == nil {
		return streamPath
	}
	return ""
}

// Close shuts down the transcoder
func (t *Transcoder) Close() {
	if t.enabled && t.queue != nil {
		close(t.queue)
	}
}