Load all themes on startup

This is the first step to allow each user to have a different theme.

template.go

@@ -4,17 +4,22 @@ import (
 	"fmt"
 	"html/template"
 	"io"
+	"io/ioutil"
 	"net/url"
+	"os"
 
 	"github.com/labstack/echo/v4"
 )
 
-type tmpl struct {
-	// TODO: add support for multiple themes
-	t *template.Template
+const themesDir = "public/themes"
+
+type renderer struct {
+	base *template.Template
+	themes map[string]*template.Template
+	defaultTheme string
 }
 
-func (t *tmpl) Render(w io.Writer, name string, data interface{}, ectx echo.Context) error {
+func (r *renderer) Render(w io.Writer, name string, data interface{}, ectx echo.Context) error {
 	// ectx is the raw *echo.context, not our own *context
 	ctx := ectx.Get("context").(*context)
 
@@ -24,10 +29,29 @@ func (t *tmpl) Render(w io.Writer, name string, data interface{}, ectx echo.Cont
 		}
 	}
 
-	return t.t.ExecuteTemplate(w, name, data)
+	// TODO: per-user theme selection
+	t := r.base
+	if r.defaultTheme != "" {
+		t = r.themes[r.defaultTheme]
+	}
+	return t.ExecuteTemplate(w, name, data)
 }
 
-func loadTemplates(logger echo.Logger, themeName string, plugins []Plugin) (*tmpl, error) {
+func loadTheme(name string, base *template.Template) (*template.Template, error) {
+	theme, err := base.Clone()
+	if err != nil {
+		return nil, err
+	}
+
+	theme, err = theme.ParseGlob("public/themes/" + name + "/*.html")
+	if err != nil {
+		return nil, err
+	}
+
+	return theme, nil
+}
+
+func loadTemplates(logger echo.Logger, defaultTheme string, plugins []Plugin) (*renderer, error) {
 	base := template.New("").Funcs(template.FuncMap{
 		"tuple": func(values ...interface{}) []interface{} {
 			return values
@@ -45,17 +69,34 @@ func loadTemplates(logger echo.Logger, themeName string, plugins []Plugin) (*tmp
 		return nil, err
 	}
 
-	theme, err := base.Clone()
-	if err != nil {
+	themes := make(map[string]*template.Template)
+
+	files, err := ioutil.ReadDir(themesDir)
+	if err != nil && !os.IsNotExist(err) {
 		return nil, err
 	}
 
-	if themeName != "" {
-		logger.Printf("Loading theme \"%s\"", themeName)
-		if _, err := theme.ParseGlob("public/themes/" + themeName + "/*.html"); err != nil {
-			return nil, err
+	for _, fi := range files {
+		if !fi.IsDir() {
+			continue
+		}
+
+		logger.Printf("Loading theme '%v'", fi.Name())
+		var err error
+		if themes[fi.Name()], err = loadTheme(fi.Name(), base); err != nil {
+			return nil, fmt.Errorf("failed to load theme '%v': %v", fi.Name(), err)
+		}
+	}
+
+	if defaultTheme != "" {
+		if _, ok := themes[defaultTheme]; !ok {
+			return nil, fmt.Errorf("failed to find default theme '%v'", defaultTheme)
 		}
 	}
 
-	return &tmpl{theme}, err
+	return &renderer{
+		base: base,
+		themes: themes,
+		defaultTheme: defaultTheme,
+	}, nil
 }