1 files changed, 38 insertions, 13 deletions
diff --git a/internal/template.go b/internal/template.go
index 4079f52..2fe9923 100644
--- a/internal/template.go
+++ b/internal/template.go
@@ -1,26 +1,51 @@
 package internal
 
 import (
+	"bytes"
 	"strings"
+	"sync"
 	gotemplate "text/template"
 )
 
 // Template stores the template for a string.
 type Template struct {
-	Src      string
-	Template *gotemplate.Template
-	ParseErr *error
+	Src        string
+	LeftDelim  string
+	RightDelim string
+
+	parseOnce      sync.Once
+	parsedTemplate *gotemplate.Template
+	parseError     error
 }
 
-func (t *Template) Parse(leftDelim, rightDelim string, funcs gotemplate.FuncMap) error {
-	if t.ParseErr == nil {
-		if strings.Contains(t.Src, leftDelim) {
-			gt, err := gotemplate.New("").Funcs(funcs).Delims(leftDelim, rightDelim).Parse(t.Src)
-			t.Template = gt
-			t.ParseErr = &err
-		} else {
-			t.ParseErr = new(error)
-		}
+func (t *Template) Execute(funcs gotemplate.FuncMap, data interface{}) (string, error) {
+	leftDelim := t.LeftDelim
+	if leftDelim == "" {
+		leftDelim = "{{"
+	}
+	if !strings.Contains(t.Src, leftDelim) {
+		// Fast path to avoid parsing a template that has no actions.
+		return t.Src, nil
+	}
+
+	var gt *gotemplate.Template
+	var err error
+	if funcs == nil {
+		t.parseOnce.Do(func() {
+			// If funcs is nil, then we only need to parse this template once.
+			t.parsedTemplate, t.parseError = gotemplate.New("").Delims(t.LeftDelim, t.RightDelim).Parse(t.Src)
+		})
+		gt, err = t.parsedTemplate, t.parseError
+	} else {
+		gt, err = gotemplate.New("").Delims(t.LeftDelim, t.RightDelim).Funcs(funcs).Parse(t.Src)
+	}
+
+	if err != nil {
+		return "", err
+	}
+	var buf bytes.Buffer
+	if err := gt.Execute(&buf, data); err != nil {
+		return "", err
 	}
-	return *t.ParseErr
+	return buf.String(), nil
 }