configurable scan parallelism based on hdd or sdd

backend/metadata/metadata.go

@@ -4,8 +4,16 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"time"
 )
 
+// ExtractionTiming holds sub-operation durations from a single
+// ExtractAllMetadata call so callers can build per-format aggregates.
+type ExtractionTiming struct {
+	TagExtraction      time.Duration
+	DurationExtraction time.Duration
+}
+
 // AudioFileExtension represents a supported audio file extension.
 type AudioFileExtension string
 
@@ -55,13 +63,16 @@ func GetTrackLengthMillis(path string) (int64, error) {
 // ExtractAllMetadata opens the file once and extracts both tags and duration.
 // This avoids the overhead of opening the file twice when both are needed.
 // If skipDuration is true, only tags are extracted and lengthMillis is 0.
+// The returned ExtractionTiming records how long each sub-operation took.
 func ExtractAllMetadata(
 	path string,
 	skipDuration bool,
-) (*TrackMetadata, int64, error) {
+) (*TrackMetadata, int64, *ExtractionTiming, error) {
+	timing := &ExtractionTiming{}
+
 	f, err := os.Open(path)
 	if err != nil {
-		return nil, 0, fmt.Errorf(
+		return nil, 0, timing, fmt.Errorf(
 			"could not open file: %w", err,
 		)
 	}
@@ -69,30 +80,40 @@ func ExtractAllMetadata(
 	defer func() { _ = f.Close() }()
 
 	// Extract tags first (reads only headers, fast).
+	tagStart := time.Now()
+
 	tags, err := ExtractTagsFromReader(f)
+
+	timing.TagExtraction = time.Since(tagStart)
+
 	if err != nil {
-		return nil, 0, fmt.Errorf(
+		return nil, 0, timing, fmt.Errorf(
 			"could not extract tags from %s: %w", path, err,
 		)
 	}
 
 	if skipDuration {
-		return tags, 0, nil
+		return tags, 0, timing, nil
 	}
 
 	// Seek back to the beginning for duration extraction.
 	if _, err := f.Seek(0, io.SeekStart); err != nil {
-		return tags, 0, fmt.Errorf(
+		return tags, 0, timing, fmt.Errorf(
 			"could not seek file for duration: %w", err,
 		)
 	}
 
+	durStart := time.Now()
+
 	lengthMillis, err := getTrackDuration(f)
+
+	timing.DurationExtraction = time.Since(durStart)
+
 	if err != nil {
-		return tags, 0, fmt.Errorf(
+		return tags, 0, timing, fmt.Errorf(
 			"error getting duration for %s: %w", path, err,
 		)
 	}
 
-	return tags, lengthMillis, nil
+	return tags, lengthMillis, timing, nil
 }