1 files changed, 74 insertions, 0 deletions
diff --git a/refstore/shorten.go b/refstore/shorten.go
new file mode 100644
index 00000000..26fa82c0
--- /dev/null
+++ b/refstore/shorten.go
@@ -0,0 +1,74 @@
+package refstore
+
+import "strings"
+
+type shortenRule struct {
+	prefix string
+	suffix string
+}
+
+var shortenRules = [...]shortenRule{
+	{prefix: "", suffix: ""},
+	{prefix: "refs/", suffix: ""},
+	{prefix: "refs/tags/", suffix: ""},
+	{prefix: "refs/heads/", suffix: ""},
+	{prefix: "refs/remotes/", suffix: ""},
+	{prefix: "refs/remotes/", suffix: "/HEAD"},
+}
+
+func (rule shortenRule) match(name string) (string, bool) {
+	if !strings.HasPrefix(name, rule.prefix) {
+		return "", false
+	}
+	if !strings.HasSuffix(name, rule.suffix) {
+		return "", false
+	}
+	short := strings.TrimPrefix(name, rule.prefix)
+	short = strings.TrimSuffix(short, rule.suffix)
+	if short == "" {
+		return "", false
+	}
+	if rule.prefix+short+rule.suffix != name {
+		return "", false
+	}
+	return short, true
+}
+
+func (rule shortenRule) render(short string) string {
+	return rule.prefix + short + rule.suffix
+}
+
+// ShortenName returns the shortest unambiguous shorthand for name among all.
+//
+// all must contain full reference names visible to the shortening scope.
+func ShortenName(name string, all []string) string {
+	names := make(map[string]struct{}, len(all))
+	for _, full := range all {
+		if full == "" {
+			continue
+		}
+		names[full] = struct{}{}
+	}
+
+	for i := len(shortenRules) - 1; i > 0; i-- {
+		short, ok := shortenRules[i].match(name)
+		if !ok {
+			continue
+		}
+		ambiguous := false
+		for j := range shortenRules {
+			if j == i {
+				continue
+			}
+			full := shortenRules[j].render(short)
+			if _, found := names[full]; found {
+				ambiguous = true
+				break
+			}
+		}
+		if !ambiguous {
+			return short
+		}
+	}
+	return name
+}