frontend: Rework asset generation

This commit reworks frontend asset generation to not need manually
written html files, but instead generate them automatically.

internal/component/static/assets.go

@@ -0,0 +1,40 @@
+package static
+
+import (
+	"html/template"
+)
+
+// Assets represents a group of assets to be included inside a template.
+//
+// Assets are generated using the 'build.mjs' script.
+// The script is called using 'go:generate', which stores variables in the form of 'Assets{{Name}}' inside this package.
+//
+// The build script roughly works as follows:
+// - Delete any previously generated distribution directory.
+// - Bundle the entrypoint sources under 'src/entry/{{Name}}/index.{ts,css}' together with the base './src/base/index.{ts,css}'
+// - Store the output inside the 'dist' directory
+// - Generate new constants of the form {{Name}}
+//
+// Each asset group should be registered as a parameter to the 'go:generate' line.
+type Assets struct {
+	Scripts string // <script> tags inserted by the asset
+	Styles  string // <link> tags inserted by the asset
+}
+
+//go:generate node build.mjs HomeHome ControlIndex ControlInstance
+
+// MustParse parses a new template from the given source
+// and registers the Asset functions to it.
+// See [Assets.RegisterFuncs].
+func (assets *Assets) MustParse(value string) *template.Template {
+	return template.Must(assets.RegisterFuncs(template.New("")).Parse(value))
+}
+
+// RegisterFuncs registers two new template functions called "JS" and "CSS".
+// Both take no arguments, and return a html-safe version of the Scripts and Style tags to be included.
+func (assets *Assets) RegisterFuncs(t *template.Template) *template.Template {
+	return t.Funcs(template.FuncMap{
+		"JS":  func() template.HTML { return template.HTML(assets.Scripts) },
+		"CSS": func() template.HTML { return template.HTML(assets.Styles) },
+	})
+}