added helper html template rendering utils

tools/template/registry.go

@@ -0,0 +1,76 @@
+// Package template is a thin wrapper arround the standard html/template
+// and text/template packages that implements a convenient registry to
+// load and cache templates on the fly concurrently.
+//
+// It was created to assist the JSVM plugin HTML rendering, but could be used in other Go code.
+//
+// Example:
+// 	registry := template.NewRegistry()
+//
+// 	html1, err := registry.LoadFiles(
+// 		// the files set wil be parsed only once and then cached
+// 		"layout.html",
+// 		"content.html",
+// 	).Render(map[string]any{"name": "John"})
+//
+// 	html2, err := registry.LoadFiles(
+// 		// reuse the already parsed and cached files set
+// 		"layout.html",
+// 		"content.html",
+// 	).Render(map[string]any{"name": "Jane"})
+package template
+
+import (
+	"html/template"
+	"strings"
+
+	"github.com/pocketbase/pocketbase/tools/store"
+)
+
+// NewRegistry creates and initializes a new blank templates registry.
+//
+// Use the Registry.Load* methods to load templates into the registry.
+func NewRegistry() *Registry {
+	return &Registry{
+		cache: store.New[*Renderer](nil),
+	}
+}
+
+// Registry defines a templates registry that is safe to be used by multiple goroutines.
+//
+// Use the Registry.Load* methods to load templates into the registry.
+type Registry struct {
+	cache *store.Store[*Renderer]
+}
+
+// LoadFiles caches (if not already) the specified files set as a
+// single template and returns a ready to use Renderer instance.
+func (r *Registry) LoadFiles(files ...string) *Renderer {
+	key := strings.Join(files, ",")
+
+	found := r.cache.Get(key)
+
+	if found == nil {
+		// parse and cache
+		tpl, err := template.ParseFiles(files...)
+		found = &Renderer{template: tpl, parseError: err}
+		r.cache.Set(key, found)
+	}
+
+	return found
+}
+
+// LoadString caches (if not already) the specified inline string as a
+// single template and returns a ready to use Renderer instance.
+func (r *Registry) LoadString(text string) *Renderer {
+	found := r.cache.Get(text)
+
+	if found == nil {
+		// parse and cache (using the text as key)
+		tpl, err := template.New("").Parse(text)
+		found = &Renderer{template: tpl, parseError: err}
+		r.cache.Set(text, found)
+	}
+
+	return found
+}