.final

backend/download_validation.go

@@ -0,0 +1,44 @@
+package backend
+
+import (
+	"fmt"
+	"math"
+)
+
+const (
+	previewMaxSeconds         = 35
+	previewExpectedMinSeconds = 60
+	largeMismatchMinExpected  = 90
+	minAllowedDurationDiff    = 15
+	durationDiffRatio         = 0.25
+)
+
+func ValidateDownloadedTrackDuration(filePath string, expectedSeconds int) (bool, error) {
+	if filePath == "" || expectedSeconds <= 0 {
+		return false, nil
+	}
+
+	actualDuration, err := GetAudioDuration(filePath)
+	if err != nil || actualDuration <= 0 {
+		return false, nil
+	}
+
+	actualSeconds := int(math.Round(actualDuration))
+	if actualSeconds <= 0 {
+		return false, nil
+	}
+
+	if expectedSeconds >= previewExpectedMinSeconds && actualSeconds <= previewMaxSeconds {
+		return true, fmt.Errorf("detected preview/sample download: file is %ds, expected about %ds. file was removed", actualSeconds, expectedSeconds)
+	}
+
+	if expectedSeconds >= largeMismatchMinExpected {
+		allowedDiff := int(math.Max(minAllowedDurationDiff, math.Round(float64(expectedSeconds)*durationDiffRatio)))
+		diff := int(math.Abs(float64(actualSeconds - expectedSeconds)))
+		if diff > allowedDiff {
+			return true, fmt.Errorf("downloaded file duration mismatch: file is %ds, expected about %ds. file was removed", actualSeconds, expectedSeconds)
+		}
+	}
+
+	return true, nil
+}