extracted cover art handling from library package

backend/coverart/coverart.go

@@ -0,0 +1,60 @@
+// Package coverart provides utilities for cover art filenames and URL resolution.
+package coverart
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+
+	"yellowjacket/backend/system"
+)
+
+// PathPrefix is the URL path prefix for cover art served by the asset handler.
+const PathPrefix = "/covers/"
+
+// URLs holds the resolved URL paths for all cover art size variants.
+type URLs struct {
+	Original string
+	Small    string
+	Medium   string
+	Large    string
+}
+
+// dirName is the subdirectory name under the user data directory
+// where cover art files are stored.
+const dirName = "covers"
+
+// CoversDir returns the absolute path to the cover art cache directory.
+func CoversDir() (string, error) {
+	dataDir, err := system.GetUserDataDirPath()
+	if err != nil {
+		return "", fmt.Errorf(
+			"could not get user data directory: %w", err,
+		)
+	}
+
+	return filepath.Join(dataDir, dirName), nil
+}
+
+// SizedFilename derives a sized-variant filename from an original cover art
+// filename and a size suffix.
+// For example, SizedFilename("a1b2c3d4.jpg", "_sm") returns "a1b2c3d4_sm.jpg".
+func SizedFilename(originalFilename, suffix string) string {
+	ext := filepath.Ext(originalFilename)
+	name := strings.TrimSuffix(originalFilename, ext)
+
+	return name + suffix + ".jpg"
+}
+
+// ResolveURLs converts a cover art filesystem path into URL paths
+// for the original and all size variants (small, medium, large).
+func ResolveURLs(filesystemPath string) URLs {
+	base := filepath.Base(filesystemPath)
+
+	return URLs{
+		Original: PathPrefix + base,
+		Small:    PathPrefix + SizedFilename(base, "_sm"),
+		Medium:   PathPrefix + SizedFilename(base, "_md"),
+		Large:    PathPrefix + SizedFilename(base, "_lg"),
+	}
+}