Implement default tags logic #150

tags.go

@@ -0,0 +1,43 @@
+package docker
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/coreos/go-semver/semver"
+)
+
+// Default tags returns a set of default suggested tags based on
+// the commit ref.
+func DefaultTags(ref string) []string {
+	if !strings.HasPrefix(ref, "refs/tags/") {
+		return []string{"latest"}
+	}
+	v := stripTagPrefix(ref)
+	version, err := semver.NewVersion(v)
+	if err != nil {
+		return []string{"latest"}
+	}
+	if version.PreRelease != "" || version.Metadata != "" {
+		return []string{
+			version.String(),
+		}
+	}
+	if version.Major == 0 {
+		return []string{
+			fmt.Sprintf("%d.%d", version.Major, version.Minor),
+			fmt.Sprintf("%d.%d.%d", version.Major, version.Minor, version.Patch),
+		}
+	}
+	return []string{
+		fmt.Sprint(version.Major),
+		fmt.Sprintf("%d.%d", version.Major, version.Minor),
+		fmt.Sprintf("%d.%d.%d", version.Major, version.Minor, version.Patch),
+	}
+}
+
+func stripTagPrefix(ref string) string {
+	ref = strings.TrimPrefix(ref, "refs/tags/")
+	ref = strings.TrimPrefix(ref, "v")
+	return ref
+}