Refactor server and templates package

internal/dis/component/server/templates/template.go

@@ -0,0 +1,65 @@
+package templates
+
+import (
+	_ "embed"
+	"html/template"
+	"text/template/parse"
+
+	"github.com/FAU-CDI/wisski-distillery/pkg/environment"
+)
+
+const (
+	footerName = "@custom/footer"
+	aboutName  = "@custom/about"
+)
+
+//go:embed "footer.html"
+var footerTemplateStr string
+var defaultFooterTemplate = template.Must(template.New("footer.html").Parse(footerTemplateStr))
+
+// Template creates a copy of template with shared template parts updated accordingly.
+// Any template using this should use one of the template contexts in this package.
+func (tpl *Templating) Template(t *template.Template) *template.Template {
+	// TODO: This should not be used!
+
+	// create a clone of the template
+	clone := template.Must(t.Clone())
+
+	// add all the fixed parse trees
+	footerTree := tpl.getTemplateAsset(defaultFooterTemplate)
+	template.Must(clone.AddParseTree(footerName, footerTree))
+
+	// optionally add the about asset
+	if aboutTree := tpl.readTemplateAsset("about.html"); clone.Lookup(aboutName) != nil && aboutTree != nil {
+		template.Must(clone.AddParseTree(aboutName, aboutTree))
+	}
+	return clone // and return the tree
+}
+
+// getTemplateAsset returns an overridable template asset.
+//
+// If the asset named can successfully be parsed, it is returned.
+// If it can not be parsed, the default template is returned.
+func (tpl *Templating) getTemplateAsset(dflt *template.Template) *parse.Tree {
+	tree := tpl.readTemplateAsset(dflt.Name())
+	if tree == nil {
+		return dflt.Tree.Copy()
+	}
+	return tree
+}
+
+// readTemplateAsset is like getTemplateAssets, but takes an explicit name to read.
+// when the asset does not exist, or cannot be opened, returns nil.
+func (tpl *Templating) readTemplateAsset(name string) *parse.Tree {
+	template, err := (func() (*template.Template, error) {
+		data, err := environment.ReadFile(tpl.Environment, tpl.CustomAssetPath(name))
+		if err != nil {
+			return nil, err
+		}
+		return template.New(name).Parse(string(data))
+	})()
+	if err != nil {
+		return nil
+	}
+	return template.Tree
+}