A simple "replacement" for `grape-entity` gem for small API projects. Allows you to create custom classes, inherit from them and get representations of both individual objects and their collections.

base.rb

# frozen_string_literal: true

module Entities
  # Fabric class to build object representation classes
  class Base
    def self.represent(...)
      new(...).represent
    end

    def self.represent_collection(collection, options = {})
      collection.map { |object| represent(object, options) }
    end

    def initialize(object, exposed_keys, options)
      @object = object
      @model_keys = exposed_keys.keys
      @mapping = exposed_keys
      @options = options
    end

    def represent
      @options.key?(:root) ? { @options[:root] => body } : body
    end

    private

    attr_reader :object

    def body
      @body ||= model_keys.index_with { |key| build_value(key) }.compact
    end

    def model_keys
      @model_keys &= Array(@options[:only]) if @options.key? :only
      @model_keys -= Array(@options[:except]) if @options.key? :except
      @model_keys
    end

    def build_value(key)
      key_method = @mapping.dig(key, :as).presence || key
      value = key_method.is_a?(Proc) ? call_to_proc(key_method) : send_to_self(key_method)
      return if @mapping.dig(key, :expose_nil) == false && value.blank?

      value = @mapping[key][:format_with].to_proc.call(value) if @mapping.dig(key, :format_with)
      value
    end

    def send_to_self(key_method)
      respond_to?(key_method, true) ? send(key_method) : object.public_send(key_method)
    end

    def call_to_proc(key_method)
      key_method.arity.zero? ? key_method.call : key_method.call(object)
    end
  end
end