Move image with cover.jpg in name to first place in Galleries (#477)

pkg/models/model_gallery.go

@@ -88,7 +88,7 @@ func (g *Gallery) readZipFile(index int) ([]byte, error) {
 func (g *Gallery) listZipContents() ([]*zip.File, *zip.ReadCloser, error) {
 	readCloser, err := zip.OpenReader(g.Path)
 	if err != nil {
-		logger.Warn("failed to read zip file")
+		logger.Warnf("failed to read zip file %s", g.Path)
 		return nil, nil, err
 	}
 
@@ -112,5 +112,41 @@ func (g *Gallery) listZipContents() ([]*zip.File, *zip.ReadCloser, error) {
 		return utils.NaturalCompare(a.Name, b.Name)
 	})
 
+	cover := contains(filteredFiles, "cover.jpg") // first image with cover.jpg in the name
+	if cover >= 0 {                               // will be moved to the start
+		reorderedFiles := reorder(filteredFiles, cover)
+		if reorderedFiles != nil {
+			return reorderedFiles, readCloser, nil
+		}
+	}
+
 	return filteredFiles, readCloser, nil
 }
+
+// return index of first occurenece of string x in name of zip contents, -1 otherwise
+func contains(a []*zip.File, x string) int {
+	for i, n := range a {
+		if strings.Contains(n.Name, x) {
+			return i
+		}
+	}
+	return -1
+}
+
+// reorder slice so that element with position toFirst gets at the start
+func reorder(a []*zip.File, toFirst int) []*zip.File {
+	var first *zip.File
+	switch {
+	case toFirst < 0 || toFirst >= len(a):
+		return nil
+	case toFirst == 0:
+		return a
+	default:
+		first = a[toFirst]
+		copy(a[toFirst:], a[toFirst+1:])     // Shift a[toFirst+1:] left one index removing a[toFirst] element
+		a[len(a)-1] = nil                    // Nil now unused element for garbage collection
+		a = a[:len(a)-1]                     // Truncate slice
+		a = append([]*zip.File{first}, a...) // Push first to the start of the slice
+	}
+	return a
+}