allow custom mail templates (#533)

internal/app/mail/template.go

@@ -6,6 +6,10 @@ import (
 	"fmt"
 	htmlTemplate "html/template"
 	"io"
+	"io/fs"
+	"log/slog"
+	"os"
+	"path/filepath"
 	"text/template"
 
 	"github.com/h44z/wg-portal/internal/domain"
@@ -22,15 +26,50 @@ type TemplateHandler struct {
 	textTemplates *template.Template
 }
 
-func newTemplateHandler(portalUrl, portalName string) (*TemplateHandler, error) {
+func newTemplateHandler(portalUrl, portalName string, basePath string) (*TemplateHandler, error) {
+	// Always parse embedded defaults first
 	htmlTemplateCache, err := htmlTemplate.New("Html").ParseFS(TemplateFiles, "tpl_files/*.gohtml")
 	if err != nil {
-		return nil, fmt.Errorf("failed to parse html template files: %w", err)
+		return nil, fmt.Errorf("failed to parse embedded html template files: %w", err)
 	}
 
 	txtTemplateCache, err := template.New("Txt").ParseFS(TemplateFiles, "tpl_files/*.gotpl")
 	if err != nil {
-		return nil, fmt.Errorf("failed to parse text template files: %w", err)
+		return nil, fmt.Errorf("failed to parse embedded text template files: %w", err)
+	}
+
+	// If a basePath is provided, ensure existence, populate if empty, then parse to override
+	if basePath != "" {
+		if err := os.MkdirAll(basePath, 0755); err != nil {
+			return nil, fmt.Errorf("failed to create templates base directory %s: %w", basePath, err)
+		}
+
+		hasTemplates, err := dirHasTemplates(basePath)
+		if err != nil {
+			return nil, fmt.Errorf("failed to inspect templates directory: %w", err)
+		}
+
+		// If no templates present, copy embedded defaults to directory
+		if !hasTemplates {
+			if err := copyEmbeddedTemplates(basePath); err != nil {
+				return nil, fmt.Errorf("failed to populate templates directory: %w", err)
+			}
+		}
+
+		// Parse files from basePath to override embedded ones.
+		// Only parse when matches exist to allow partial overrides without errors.
+		if matches, _ := filepath.Glob(filepath.Join(basePath, "*.gohtml")); len(matches) > 0 {
+			slog.Debug("parsing html email templates from base path", "base-path", basePath, "files", matches)
+			if htmlTemplateCache, err = htmlTemplateCache.ParseFiles(matches...); err != nil {
+				return nil, fmt.Errorf("failed to parse html templates from base path: %w", err)
+			}
+		}
+		if matches, _ := filepath.Glob(filepath.Join(basePath, "*.gotpl")); len(matches) > 0 {
+			slog.Debug("parsing text email templates from base path", "base-path", basePath, "files", matches)
+			if txtTemplateCache, err = txtTemplateCache.ParseFiles(matches...); err != nil {
+				return nil, fmt.Errorf("failed to parse text templates from base path: %w", err)
+			}
+		}
 	}
 
 	handler := &TemplateHandler{
@@ -43,24 +82,71 @@ func newTemplateHandler(portalUrl, portalName string) (*TemplateHandler, error)
 	return handler, nil
 }
 
+// dirHasTemplates checks whether directory contains any .gohtml or .gotpl files.
+func dirHasTemplates(basePath string) (bool, error) {
+	entries, err := os.ReadDir(basePath)
+	if err != nil {
+		return false, err
+	}
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		ext := filepath.Ext(e.Name())
+		if ext == ".gohtml" || ext == ".gotpl" {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+// copyEmbeddedTemplates writes embedded templates into basePath.
+func copyEmbeddedTemplates(basePath string) error {
+	list, err := fs.ReadDir(TemplateFiles, "tpl_files")
+	if err != nil {
+		return err
+	}
+	for _, entry := range list {
+		if entry.IsDir() {
+			continue
+		}
+		name := entry.Name()
+		// Only copy known template extensions
+		if ext := filepath.Ext(name); ext != ".gohtml" && ext != ".gotpl" {
+			continue
+		}
+		data, err := TemplateFiles.ReadFile(filepath.Join("tpl_files", name))
+		if err != nil {
+			return err
+		}
+		out := filepath.Join(basePath, name)
+		if err := os.WriteFile(out, data, 0644); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // GetConfigMail returns the text and html template for the mail with a link.
 func (c TemplateHandler) GetConfigMail(user *domain.User, link string) (io.Reader, io.Reader, error) {
 	var tplBuff bytes.Buffer
 	var htmlTplBuff bytes.Buffer
 
 	err := c.textTemplates.ExecuteTemplate(&tplBuff, "mail_with_link.gotpl", map[string]any{
-		"User":      user,
-		"Link":      link,
-		"PortalUrl": c.portalUrl,
+		"User":       user,
+		"Link":       link,
+		"PortalUrl":  c.portalUrl,
+		"PortalName": c.portalName,
 	})
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to execute template mail_with_link.gotpl: %w", err)
 	}
 
 	err = c.htmlTemplates.ExecuteTemplate(&htmlTplBuff, "mail_with_link.gohtml", map[string]any{
-		"User":      user,
-		"Link":      link,
-		"PortalUrl": c.portalUrl,
+		"User":       user,
+		"Link":       link,
+		"PortalUrl":  c.portalUrl,
+		"PortalName": c.portalName,
 	})
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to execute template mail_with_link.gohtml: %w", err)