feat: add apiresource

Author: roman-vanesyan

apiresource/apiresource.go

@@ -0,0 +1,68 @@
+// Package apiresource implements an API resource management as described in
+// https://brandur.org/two-phase-render
+package apiresource
+
+import (
+	"context"
+	"fmt"
+)
+
+type Renderable[TBundle any, TEntity any, TResource any, TParams any] interface {
+	Bundle(context.Context, TParams, []TEntity) (TBundle, error)
+	Render(context.Context, TParams, TBundle, TEntity) (TResource, error)
+}
+
+// Render renders an API resource.
+func Render[
+	TRenderable Renderable[TBundle, TEntity, TRenderable, TParams],
+	TBundle any,
+	TEntity any,
+	TParams any,
+](
+	ctx context.Context,
+	params TParams,
+	entity TEntity,
+) (TRenderable, error) {
+	var renderable TRenderable
+
+	bundle, err := renderable.Bundle(ctx, params, []TEntity{entity})
+	if err != nil {
+		return renderable, fmt.Errorf("apiresource: error loading bundle: %w", err)
+	}
+
+	resource, err := renderable.Render(ctx, params, bundle, entity)
+	if err != nil {
+		return renderable, fmt.Errorf("apiresource: error rendering resource: %w", err)
+	}
+
+	return resource, nil
+}
+
+// RenderMany is similar to Render, but renders many API resources at once.
+func RenderMany[
+	TBundle any,
+	TRenderable Renderable[TBundle, TEntity, TRenderable, TParams],
+	TEntity any,
+	TParams any,
+](
+	ctx context.Context,
+	params TParams,
+	entities []TEntity,
+) ([]TRenderable, error) {
+	var renderable TRenderable
+
+	bundle, err := renderable.Bundle(ctx, params, entities)
+	if err != nil {
+		return nil, fmt.Errorf("apiresource: error loading bundle: %w", err)
+	}
+
+	resources := make([]TRenderable, len(entities))
+	for i := range resources {
+		resources[i], err = renderable.Render(ctx, params, bundle, entities[i])
+		if err != nil {
+			return nil, fmt.Errorf("apiresource: error rendering resource: %w", err)
+		}
+	}
+
+	return resources, nil
+}