added template expand helper

bird/utils.go

@@ -0,0 +1,20 @@
+package bird
+
+import (
+	"regexp"
+)
+
+/*
+ Template Replace:
+ See https://golang.org/pkg/regexp/#Regexp.Expand
+ for a template reference.
+*/
+func TemplateExpand(expr, template, input string) string {
+	reg := regexp.MustCompile(expr)
+	match := reg.FindStringSubmatchIndex(input)
+
+	dst := []byte{}
+	res := reg.ExpandString(dst, template, input, match)
+
+	return string(res)
+}

bird/utils_test.go

@@ -0,0 +1,26 @@
+package bird
+
+import (
+	"testing"
+)
+
+func TestTemplateExpand(t *testing.T) {
+	// Expect input to be something like
+	//   TEST_FOO_42_src
+	//
+	// Template:
+	//   RESULT_$1
+	//
+	// Result:
+	//    RESULT_FOO_42
+	//
+	src := "TEST_FOO_42_src"
+	expr := `TEST_(.*)_src`
+	tmpl := "RESULT_${1}_${1}"
+
+	res := TemplateExpand(expr, tmpl, src)
+
+	if res != "RESULT_FOO_42_FOO_42" {
+		t.Error("Unexpacted expansion:", res)
+	}
+}