feat(email): improve email templating (#27)

backend/internal/utils/email/email_service_templates.go

@@ -0,0 +1,97 @@
+package email
+
+import (
+	"fmt"
+	htemplate "html/template"
+	"io/fs"
+	"path"
+	ttemplate "text/template"
+)
+
+const templateComponentsDir = "components"
+
+type Template[V any] struct {
+	Path  string
+	Title func(data *TemplateData[V]) string
+}
+
+type TemplateData[V any] struct {
+	AppName string
+	LogoURL string
+	Data    *V
+}
+
+type TemplateMap[V any] map[string]*V
+
+func GetTemplate[U any, V any](templateMap TemplateMap[U], template Template[V]) *U {
+	return templateMap[template.Path]
+}
+
+type clonable[V pareseable[V]] interface {
+	Clone() (V, error)
+}
+
+type pareseable[V any] interface {
+	ParseFS(fs.FS, ...string) (V, error)
+}
+
+func prepareTemplate[V pareseable[V]](template string, rootTemplate clonable[V], templateDir fs.FS, suffix string) (V, error) {
+	tmpl, err := rootTemplate.Clone()
+	if err != nil {
+		return *new(V), fmt.Errorf("clone root html template: %w", err)
+	}
+
+	filename := fmt.Sprintf("%s%s", template, suffix)
+	_, err = tmpl.ParseFS(templateDir, filename)
+	if err != nil {
+		return *new(V), fmt.Errorf("parsing html template '%s': %w", template, err)
+	}
+
+	return tmpl, nil
+}
+
+func PrepareTextTemplates(templateDir fs.FS, templates []string) (map[string]*ttemplate.Template, error) {
+	components := path.Join(templateComponentsDir, "*_text.tmpl")
+	rootTmpl, err := ttemplate.ParseFS(templateDir, components)
+	if err != nil {
+		return nil, fmt.Errorf("unable to parse templates '%s': %w", components, err)
+	}
+
+	var textTemplates = make(map[string]*ttemplate.Template, len(templates))
+	for _, tmpl := range templates {
+		rootTmplClone, err := rootTmpl.Clone()
+		if err != nil {
+			return nil, fmt.Errorf("clone root template: %w", err)
+		}
+
+		textTemplates[tmpl], err = prepareTemplate[*ttemplate.Template](tmpl, rootTmplClone, templateDir, "_text.tmpl")
+		if err != nil {
+			return nil, fmt.Errorf("parse '%s': %w", tmpl, err)
+		}
+	}
+
+	return textTemplates, nil
+}
+
+func PrepareHTMLTemplates(templateDir fs.FS, templates []string) (map[string]*htemplate.Template, error) {
+	components := path.Join(templateComponentsDir, "*_html.tmpl")
+	rootTmpl, err := htemplate.ParseFS(templateDir, components)
+	if err != nil {
+		return nil, fmt.Errorf("unable to parse templates '%s': %w", components, err)
+	}
+
+	var htmlTemplates = make(map[string]*htemplate.Template, len(templates))
+	for _, tmpl := range templates {
+		rootTmplClone, err := rootTmpl.Clone()
+		if err != nil {
+			return nil, fmt.Errorf("clone root template: %w", err)
+		}
+
+		htmlTemplates[tmpl], err = prepareTemplate[*htemplate.Template](tmpl, rootTmplClone, templateDir, "_html.tmpl")
+		if err != nil {
+			return nil, fmt.Errorf("parse '%s': %w", tmpl, err)
+		}
+	}
+
+	return htmlTemplates, nil
+}