refactor: yet another one, someday I might be happy

renderer.go

@@ -13,15 +13,32 @@ var ErrUnsupportedFormat = fmt.Errorf("%w: unsupported format", Err)
 // Renderer is a renderer that delegates rendering to another renderer
 // based on a format value.
 type Renderer struct {
-	// Formats is a map of format names to renderers. When Render is called,
+	// Renderers is a map of format names to renderers. When Render is called,
 	// the format is used to look up the renderer to use.
-	Formats map[string]FormatRenderer
+	Renderers map[string]FormatRenderer
 }
 
-// NewFormatRenderer returns a new FormatRenderer that delegates rendering to
-// the specified renderers.
-func NewFormatRenderer(formats map[string]FormatRenderer) *Renderer {
-	return &Renderer{Formats: formats}
+// New returns a new Renderer that delegates rendering to the specified
+// renderers.
+//
+// Any renderers which implement the Formats interface, will also be set as the
+// renderer for all format strings returned by Format() on the renderer.
+func New(renderers map[string]FormatRenderer) *Renderer {
+	newRenderers := make(map[string]FormatRenderer, len(renderers))
+
+	for format, r := range renderers {
+		newRenderers[format] = r
+
+		if x, ok := r.(Formats); ok {
+			for _, f := range x.Formats() {
+				if f != format {
+					newRenderers[f] = r
+				}
+			}
+		}
+	}
+
+	return &Renderer{Renderers: newRenderers}
 }
 
 // Render renders a value to an io.Writer using the specified format. If the
@@ -32,7 +49,7 @@ func NewFormatRenderer(formats map[string]FormatRenderer) *Renderer {
 // ErrCannotRender, but it could be a different error if the renderer returns
 // one.
 func (r *Renderer) Render(w io.Writer, format string, v any) error {
-	renderer, ok := r.Formats[format]
+	renderer, ok := r.Renderers[format]
 	if !ok {
 		return fmt.Errorf("%w: %s", ErrUnsupportedFormat, format)
 	}
@@ -51,3 +68,15 @@ func (r *Renderer) Render(w io.Writer, format string, v any) error {
 
 	return nil
 }
+
+func (r *Renderer) OnlyWith(formats ...string) *Renderer {
+	renderers := make(map[string]FormatRenderer, len(formats))
+
+	for _, format := range formats {
+		if r, ok := r.Renderers[format]; ok {
+			renderers[format] = r
+		}
+	}
+
+	return New(renderers)
+}