Make active_model_serializers render Pagy result as jsonapi response, with pagination meta and links

application_controller.rb

class Api::ApplicationController < ActionController::API
  include Pagy::Backend
  include PagyCollectionSerializer::ControllerMixin
end

departments_controller.rb

class Api::V1::DepartmentsController < Api::ApplicationController
  def index
    render json: pagy(Current.organization.departments)
  end
end

pagy_collection_serializer.rb

require 'securerandom'

class PagyCollectionSerializer < ActiveModel::Serializer::CollectionSerializer
  module ControllerMixin
    def pagy_get_vars(collection, vars)
      super.tap do |result|
        result[:page] = params.dig(:page, :number)
        result[:items] = params.dig(:page, :size).to_i
        result[:items] = 10 if result[:items] <= 0
        result[:items] = 100 if result[:items] > 100
      end
    end

    %i[_render_option_json _render_with_renderer_json].each do |renderer_method|
      define_method renderer_method do |resource, options|
        if resource.is_a?(Array) && resource.length == 2 && resource[0].is_a?(Pagy)
          options[:serializer] ||= PagyCollectionSerializer

          pagy = resource[0]

          unless options.key?(:meta)
            options[:meta] = {
              total_count: pagy.count,
              current_page: pagy.page,
              page_size: pagy.items,
              prev_page: pagy.prev,
              next_page: pagy.next
            }

            options[:meta].merge! options.delete(:merge_meta) if options.key?(:merge_meta)
          end

        end
        super(resource, options)
      end
    end
  end

  module ModelMixin
    METHOD_NAME = "pagy_from_pagy_collection_serializer".freeze

    def self.mount(pagy, collection)
      return if collection.instance_variable_defined?("@#{METHOD_NAME}")

      collection.instance_variable_set("@#{METHOD_NAME}", pagy)
      collection.define_singleton_method(METHOD_NAME) { instance_variable_get("@#{METHOD_NAME}") }
      collection.extend(self)
    end

    def current_page
      pagy_from_pagy_collection_serializer.page
    end

    def total_pages
      pagy_from_pagy_collection_serializer.pages
    end

    def next_page
      pagy_from_pagy_collection_serializer.next
    end

    def per_page
      pagy_from_pagy_collection_serializer.items
    end
  end

  def initialize(pagy_result, options = {})
    pagy, collection = pagy_result
    ModelMixin.mount(pagy, collection)
    super(collection, options)
  end

  def paginated?
    true
  end
end

response.json

{
    "data": [
        {
            "id": "14",
            "type": "departments",
            "attributes": {
                "name": "t5",
                "created_at": "2023-12-31T18:15:26.614+08:00",
                "updated_at": "2023-12-31T18:15:26.614+08:00",
                "parent_id": 10,
                "employees_count": 0
            }
        },
        {
            "id": "15",
            "type": "departments",
            "attributes": {
                "name": "t5",
                "created_at": "2023-12-31T18:15:48.624+08:00",
                "updated_at": "2023-12-31T18:15:48.624+08:00",
                "parent_id": 11,
                "employees_count": 0
            }
        },
        {
            "id": "16",
            "type": "departments",
            "attributes": {
                "name": "t15",
                "created_at": "2023-12-31T18:15:54.594+08:00",
                "updated_at": "2023-12-31T18:15:54.594+08:00",
                "parent_id": 11,
                "employees_count": 0
            }
        }
    ],
    "links": {
        "self": "http://open.lvh.me:3000/api/v1/departments?page%5Bnumber%5D=2&page%5Bsize%5D=5",
        "first": "http://open.lvh.me:3000/api/v1/departments?page%5Bnumber%5D=1&page%5Bsize%5D=5",
        "prev": "http://open.lvh.me:3000/api/v1/departments?page%5Bnumber%5D=1&page%5Bsize%5D=5",
        "next": null,
        "last": "http://open.lvh.me:3000/api/v1/departments?page%5Bnumber%5D=2&page%5Bsize%5D=5"
    },
    "meta": {
        "total_count": 8,
        "current_page": 2,
        "page_size": 5,
        "prev_page": 1,
        "next_page": null
    }
}