Refactors Cover's Extension cleaning in Album

album.go

@@ -1,8 +1,10 @@
 package main
 
 import (
+	"path"
 	"regexp"
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -101,3 +103,14 @@ func (a *Album) String() string {
 	}
 	return res + a.Title
 }
+
+var rxExt = regexp.MustCompile(`\.([0-9]+)([a-zA-Z]+)\z`)
+
+func (a *Album) CoverExt() string {
+	ext := path.Ext(a.CoverURL)
+	m := rxExt.FindStringSubmatch(ext)
+	if m != nil {
+		ext = "." + m[2]
+	}
+	return strings.ToLower(ext)
+}