fix(templating): simplify template API and make it optional

pkg/services/standard/standard.go

@@ -3,7 +3,6 @@ package standard
 // Standard implements the Logger and Templater parts of the Service interface
 type Standard struct {
 	Logger
-	Templater
 	Initializer
 	QueuedSender
 }

pkg/services/standard/standard_templater.go

@@ -1,26 +1,36 @@
 package standard
 
 import (
-	"strings"
+	"io/ioutil"
 	"text/template"
 )
 
 // Templater is the standard implementation of ApplyTemplate using the "text/template" library
-type Templater struct {}
+type Templater struct {
+	templates map[string]*template.Template
+}
 
-// ApplyTemplate applies the params to the input template and returns the result
-func (templater *Templater) ApplyTemplate (tpl string, params *map[string]string) (string, error) {
-	engine, err := template.New("").Parse(tpl);
+// GetTemplate attempts to retrieve the template identified with id
+func (templater *Templater) GetTemplate (id string) (template *template.Template, found bool) {
+	tpl, found := templater.templates[id]
+	return tpl, found
+}
+
+// SetTemplateString creates a new template from the body and assigning it the id
+func (templater *Templater) SetTemplateString (id string, body string) error {
+	tpl, err := template.New("").Parse(body)
 	if err != nil {
-		return "", err
+		return err
 	}
+	templater.templates[id] = tpl
+	return nil
+}
 
-	writer := strings.Builder{}
-
-	if err := engine.Execute(&writer, params); err != nil {
-		return "", err
+// SetTemplateFile creates a new template from the file and assigning it the id
+func (templater *Templater) SetTemplateFile (id string, file string) error {
+	bytes, err := ioutil.ReadFile(file)
+	if err != nil {
+		return err
 	}
-
-	return writer.String(), err
-
+	return templater.SetTemplateString(id, string(bytes))
 }