VT_Player/internal/keyframe/detector.go

package keyframe

import (
	"context"
	"crypto/md5"
	"encoding/binary"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.leaktechnologies.dev/stu/VT_Player/internal/logging"
)

// Keyframe represents an I-frame position in a video
type Keyframe struct {
	FrameNum  int     // Frame number (0-indexed)
	Timestamp float64 // Time in seconds
}

// Index holds keyframe positions for a video
// Only stores I-frames for memory efficiency (~1KB per minute of video)
type Index struct {
	Keyframes   []Keyframe // Only I-frames, not all frames
	TotalFrames int        // Total number of frames in video
	Duration    float64    // Duration in seconds
	FrameRate   float64    // Average frame rate
	VideoPath   string     // Path to source video
	CreatedAt   time.Time  // When index was created
}

// DetectKeyframes uses ffprobe to find I-frames (keyframes) in a video
// Performance target: <5s for 1-hour video, <10MB memory overhead
func DetectKeyframes(videoPath string) (*Index, error) {
	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
	defer cancel()

	logging.Debug(logging.CatFFMPEG, "detecting keyframes for %s", videoPath)
	startTime := time.Now()

	// Get video metadata first (duration, framerate)
	metadata, err := getVideoMetadata(ctx, videoPath)
	if err != nil {
		return nil, fmt.Errorf("failed to get video metadata: %w", err)
	}

	// Use ffprobe to extract keyframes via packet flags
	// Packets with 'K' flag are keyframes (I-frames)
	// This is faster than decoding frames
	cmd := exec.CommandContext(ctx, "ffprobe",
		"-v", "error",
		"-select_streams", "v:0",
		"-show_entries", "packet=pts_time,flags",
		"-of", "csv=p=0",
		videoPath,
	)

	output, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("ffprobe keyframe detection failed: %w", err)
	}

	// Parse keyframe timestamps
	// Format: pts_time,flags (e.g., "0.000000,K_" for keyframe or "0.033367,__" for non-keyframe)
	lines := strings.Split(strings.TrimSpace(string(output)), "\n")
	keyframes := make([]Keyframe, 0, len(lines)/10) // Estimate: ~10% are keyframes

	for _, line := range lines {
		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}

		parts := strings.Split(line, ",")
		if len(parts) != 2 {
			continue
		}

		// Check if this is a keyframe (flags contains 'K')
		isKeyframe := strings.Contains(parts[1], "K")
		if !isKeyframe {
			continue
		}

		timestamp, err := strconv.ParseFloat(parts[0], 64)
		if err != nil {
			logging.Debug(logging.CatFFMPEG, "failed to parse keyframe timestamp '%s': %v", parts[0], err)
			continue
		}

		// Calculate frame number from timestamp
		frameNum := int(timestamp * metadata.FrameRate)

		keyframes = append(keyframes, Keyframe{
			FrameNum:  frameNum,
			Timestamp: timestamp,
		})
	}

	elapsed := time.Since(startTime)
	logging.Debug(logging.CatFFMPEG, "detected %d keyframes in %.2fs (%.0f keyframes/sec)",
		len(keyframes), elapsed.Seconds(), float64(len(keyframes))/elapsed.Seconds())

	idx := &Index{
		Keyframes:   keyframes,
		TotalFrames: int(metadata.Duration * metadata.FrameRate),
		Duration:    metadata.Duration,
		FrameRate:   metadata.FrameRate,
		VideoPath:   videoPath,
		CreatedAt:   time.Now(),
	}

	return idx, nil
}

// videoMetadata holds basic video information needed for keyframe detection
type videoMetadata struct {
	Duration  float64
	FrameRate float64
}

// getVideoMetadata extracts duration and framerate from video
func getVideoMetadata(ctx context.Context, videoPath string) (*videoMetadata, error) {
	// Get duration from format (more reliable than stream duration)
	durationCmd := exec.CommandContext(ctx, "ffprobe",
		"-v", "error",
		"-show_entries", "format=duration",
		"-of", "csv=p=0",
		videoPath,
	)

	durationOut, err := durationCmd.Output()
	if err != nil {
		return nil, fmt.Errorf("failed to get duration: %w", err)
	}

	duration, err := strconv.ParseFloat(strings.TrimSpace(string(durationOut)), 64)
	if err != nil {
		return nil, fmt.Errorf("invalid duration: %w", err)
	}

	// Get frame rate from stream
	framerateCmd := exec.CommandContext(ctx, "ffprobe",
		"-v", "error",
		"-select_streams", "v:0",
		"-show_entries", "stream=avg_frame_rate",
		"-of", "csv=p=0",
		videoPath,
	)

	framerateOut, err := framerateCmd.Output()
	if err != nil {
		return nil, fmt.Errorf("failed to get framerate: %w", err)
	}

	// Parse frame rate (format: "num/den" like "30000/1001")
	frameRate := parseFrameRate(strings.TrimSpace(string(framerateOut)))
	if frameRate <= 0 {
		frameRate = 30.0 // Default fallback
	}

	return &videoMetadata{
		Duration:  duration,
		FrameRate: frameRate,
	}, nil
}

// parseFrameRate parses ffprobe frame rate format "num/den"
func parseFrameRate(rateStr string) float64 {
	parts := strings.Split(rateStr, "/")
	if len(parts) != 2 {
		return 0
	}

	num, err1 := strconv.ParseFloat(parts[0], 64)
	den, err2 := strconv.ParseFloat(parts[1], 64)
	if err1 != nil || err2 != nil || den == 0 {
		return 0
	}

	return num / den
}

// FindNearestKeyframe returns the closest keyframe to the given timestamp
// direction: "before" (<=), "after" (>=), "nearest" (closest)
func (idx *Index) FindNearestKeyframe(timestamp float64, direction string) *Keyframe {
	if len(idx.Keyframes) == 0 {
		return nil
	}

	switch direction {
	case "before":
		return idx.findBefore(timestamp)
	case "after":
		return idx.findAfter(timestamp)
	case "nearest":
		return idx.findNearest(timestamp)
	default:
		return idx.findNearest(timestamp)
	}
}

// findBefore finds the last keyframe at or before timestamp (binary search)
func (idx *Index) findBefore(timestamp float64) *Keyframe {
	if len(idx.Keyframes) == 0 {
		return nil
	}

	// Binary search for insertion point
	i := sort.Search(len(idx.Keyframes), func(i int) bool {
		return idx.Keyframes[i].Timestamp > timestamp
	})

	// i is the first keyframe after timestamp
	// We want the one before it
	if i == 0 {
		// All keyframes are after timestamp, return first one
		return &idx.Keyframes[0]
	}

	return &idx.Keyframes[i-1]
}

// findAfter finds the first keyframe at or after timestamp (binary search)
func (idx *Index) findAfter(timestamp float64) *Keyframe {
	if len(idx.Keyframes) == 0 {
		return nil
	}

	// Binary search for insertion point
	i := sort.Search(len(idx.Keyframes), func(i int) bool {
		return idx.Keyframes[i].Timestamp >= timestamp
	})

	if i >= len(idx.Keyframes) {
		// All keyframes are before timestamp, return last one
		return &idx.Keyframes[len(idx.Keyframes)-1]
	}

	return &idx.Keyframes[i]
}

// findNearest finds the closest keyframe to timestamp
func (idx *Index) findNearest(timestamp float64) *Keyframe {
	if len(idx.Keyframes) == 0 {
		return nil
	}

	before := idx.findBefore(timestamp)
	after := idx.findAfter(timestamp)

	// If they're the same, return it
	if before == after {
		return before
	}

	// Return whichever is closer
	beforeDist := timestamp - before.Timestamp
	afterDist := after.Timestamp - timestamp

	if beforeDist <= afterDist {
		return before
	}
	return after
}

// EstimateFrameNumber calculates frame number from timestamp
func (idx *Index) EstimateFrameNumber(timestamp float64) int {
	if idx.FrameRate <= 0 {
		return 0
	}
	return int(timestamp*idx.FrameRate + 0.5)
}

// GetKeyframeAt returns the keyframe at the given index, or nil if out of range
func (idx *Index) GetKeyframeAt(i int) *Keyframe {
	if i < 0 || i >= len(idx.Keyframes) {
		return nil
	}
	return &idx.Keyframes[i]
}

// NumKeyframes returns the total number of keyframes
func (idx *Index) NumKeyframes() int {
	return len(idx.Keyframes)
}

// GetCacheKey generates a unique cache key for a video file
// Based on file path and modification time to invalidate cache when file changes
func GetCacheKey(videoPath string) (string, error) {
	info, err := os.Stat(videoPath)
	if err != nil {
		return "", err
	}

	// Create hash of path + mod time
	h := md5.New()
	h.Write([]byte(videoPath))
	binary.Write(h, binary.LittleEndian, info.ModTime().Unix())

	return fmt.Sprintf("%x", h.Sum(nil)), nil
}

// GetCacheDir returns the directory for keyframe cache files
func GetCacheDir() (string, error) {
	homeDir, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}

	cacheDir := filepath.Join(homeDir, ".cache", "vt_player", "keyframes")
	if err := os.MkdirAll(cacheDir, 0755); err != nil {
		return "", err
	}

	return cacheDir, nil
}

// SaveToCache saves the keyframe index to disk cache
func (idx *Index) SaveToCache() error {
	cacheKey, err := GetCacheKey(idx.VideoPath)
	if err != nil {
		return err
	}

	cacheDir, err := GetCacheDir()
	if err != nil {
		return err
	}

	cachePath := filepath.Join(cacheDir, cacheKey+".kf")

	f, err := os.Create(cachePath)
	if err != nil {
		return err
	}
	defer f.Close()

	// Write binary format:
	// [num_keyframes:4][duration:8][framerate:8]
	// [timestamp:8][frame_num:4]... (repeated for each keyframe)

	if err := binary.Write(f, binary.LittleEndian, int32(len(idx.Keyframes))); err != nil {
		return err
	}
	if err := binary.Write(f, binary.LittleEndian, idx.Duration); err != nil {
		return err
	}
	if err := binary.Write(f, binary.LittleEndian, idx.FrameRate); err != nil {
		return err
	}

	for _, kf := range idx.Keyframes {
		if err := binary.Write(f, binary.LittleEndian, kf.Timestamp); err != nil {
			return err
		}
		if err := binary.Write(f, binary.LittleEndian, int32(kf.FrameNum)); err != nil {
			return err
		}
	}

	logging.Debug(logging.CatFFMPEG, "saved keyframe cache: %s (%d keyframes, %.1fKB)",
		cachePath, len(idx.Keyframes), float64(len(idx.Keyframes)*12)/1024.0)

	return nil
}

// LoadFromCache loads keyframe index from disk cache
func LoadFromCache(videoPath string) (*Index, error) {
	cacheKey, err := GetCacheKey(videoPath)
	if err != nil {
		return nil, err
	}

	cacheDir, err := GetCacheDir()
	if err != nil {
		return nil, err
	}

	cachePath := filepath.Join(cacheDir, cacheKey+".kf")

	f, err := os.Open(cachePath)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var numKeyframes int32
	if err := binary.Read(f, binary.LittleEndian, &numKeyframes); err != nil {
		return nil, err
	}

	var duration, frameRate float64
	if err := binary.Read(f, binary.LittleEndian, &duration); err != nil {
		return nil, err
	}
	if err := binary.Read(f, binary.LittleEndian, &frameRate); err != nil {
		return nil, err
	}

	keyframes := make([]Keyframe, numKeyframes)
	for i := range keyframes {
		if err := binary.Read(f, binary.LittleEndian, &keyframes[i].Timestamp); err != nil {
			return nil, err
		}
		var frameNum int32
		if err := binary.Read(f, binary.LittleEndian, &frameNum); err != nil {
			return nil, err
		}
		keyframes[i].FrameNum = int(frameNum)
	}

	idx := &Index{
		Keyframes:   keyframes,
		TotalFrames: int(duration * frameRate),
		Duration:    duration,
		FrameRate:   frameRate,
		VideoPath:   videoPath,
		CreatedAt:   time.Now(), // Cache load time
	}

	logging.Debug(logging.CatFFMPEG, "loaded keyframe cache: %s (%d keyframes)",
		cachePath, len(keyframes))

	return idx, nil
}

// DetectKeyframesWithCache attempts to load from cache, falls back to detection
func DetectKeyframesWithCache(videoPath string) (*Index, error) {
	// Try cache first
	idx, err := LoadFromCache(videoPath)
	if err == nil {
		logging.Debug(logging.CatFFMPEG, "using cached keyframes for %s", videoPath)
		return idx, nil
	}

	// Cache miss or error, detect keyframes
	logging.Debug(logging.CatFFMPEG, "cache miss, detecting keyframes for %s", videoPath)
	idx, err = DetectKeyframes(videoPath)
	if err != nil {
		return nil, err
	}

	// Save to cache for next time
	if err := idx.SaveToCache(); err != nil {
		logging.Debug(logging.CatFFMPEG, "failed to save keyframe cache: %v", err)
		// Don't fail if cache save fails
	}

	return idx, nil
}

// CleanCache removes old cache files (older than maxAge)
func CleanCache(maxAge time.Duration) error {
	cacheDir, err := GetCacheDir()
	if err != nil {
		return err
	}

	entries, err := os.ReadDir(cacheDir)
	if err != nil {
		return err
	}

	now := time.Now()
	removed := 0

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}

		if !strings.HasSuffix(entry.Name(), ".kf") {
			continue
		}

		info, err := entry.Info()
		if err != nil {
			continue
		}

		age := now.Sub(info.ModTime())
		if age > maxAge {
			path := filepath.Join(cacheDir, entry.Name())
			if err := os.Remove(path); err != nil {
				logging.Debug(logging.CatFFMPEG, "failed to remove old cache file %s: %v", path, err)
			} else {
				removed++
			}
		}
	}

	if removed > 0 {
		logging.Debug(logging.CatFFMPEG, "cleaned %d old keyframe cache files", removed)
	}

	return nil
}

// GetCacheSize returns total size of cache directory in bytes
func GetCacheSize() (int64, error) {
	cacheDir, err := GetCacheDir()
	if err != nil {
		return 0, err
	}

	var totalSize int64

	err = filepath.Walk(cacheDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if !info.IsDir() {
			totalSize += info.Size()
		}
		return nil
	})

	return totalSize, err
}