feat: better file sorting

pkg/gotenberg/sort.go

@@ -0,0 +1,69 @@
+package gotenberg
+
+import (
+	"regexp"
+	"sort"
+	"strconv"
+)
+
+// AlphanumericSort implements sort.Interface and helps to sort strings
+// alphanumerically.
+//
+// See https://github.com/gotenberg/gotenberg/issues/805.
+type AlphanumericSort []string
+
+func (s AlphanumericSort) Len() int {
+	return len(s)
+}
+
+func (s AlphanumericSort) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
+func (s AlphanumericSort) Less(i, j int) bool {
+	numI, restI := extractPrefix(s[i])
+	numJ, restJ := extractPrefix(s[j])
+
+	// Compares numerical prefixes if they exist.
+	if numI != -1 && numJ != -1 {
+		if numI != numJ {
+			return numI < numJ
+		}
+		// If numbers are equal, falls back to string comparison of the rest.
+		return restI < restJ
+	}
+
+	// If one has a numerical prefix and the other doesn't, the one with the
+	// number comes first.
+	if numI != -1 {
+		return true
+	}
+	if numJ != -1 {
+		return false
+	}
+
+	// If neither has a numerical prefix, compare as strings
+	return s[i] < s[j]
+}
+
+// extractPrefix attempts to extract a numerical prefix and the rest of the filename
+func extractPrefix(filename string) (int, string) {
+	matches := numPrefixRegexp.FindStringSubmatch(filename)
+	if len(matches) > 2 {
+		prefix, err := strconv.Atoi(matches[1])
+		if err == nil {
+			return prefix, matches[2]
+		}
+	}
+
+	// Returns -1 if no numerical prefix is found, indicating to just compare
+	// as strings.
+	return -1, filename
+}
+
+var numPrefixRegexp = regexp.MustCompile(`^(\d+)(.*)$`)
+
+// Interface guard.
+var (
+	_ sort.Interface = (*AlphanumericSort)(nil)
+)