# app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  include ErrorsHelper
end

# app/controllers/concerns/errors_helper.rb

module ErrorsHelper
  extend ActiveSupport::Concern

  included do
    rescue_from ActionController::ParameterMissing, with: :unprocessable_entity
    rescue_from ActiveRecord::RecordNotFound, with: :record_not_found
    rescue_from ArgumentError, with: :unprocessable_entity
    rescue_from MyCustomError, with: :render_my_custom_error
    rescue_from Pundit::NotAuthorizedError, with: :unauthorized
    # ...

    rescue_from InvalidSchemaError do |e|
      render json: { message: e.message }, status: :bad_request
    end
  end

  private

  def render_error(error, status)
    render json: { errors: [error] }, status: status
  end

  def unprocessable_entity(error)
    render_error(error, :unprocessable_entity)
  end

  def record_not_found(error)
    render_error(error, :not_found)
  end

  def unauthorized
    head(:unauthorized)
  end

  def render_my_custom_error
    render_error(MyCustomError.new.message, :not_acceptable)
  end
end

# app/errors/invalid_schema_error.rb

class InvalidSchemaError < StandardError
  def message
    "Provided parameters doesn't validate with the expected schema"
  end
end

# app/errors/my_custom_error.rb

class MyCustomError < StandardError
  def message
    "Custom error, error message"
  end
end

# Gemfile

# ...
gem 'errors_savior'
# ...

# config/initializers/errors_savior.rb

ErrorsSavior.configure do |config|
  # ErrorsSavior needs your api_origin metadata if you like to show this information on responses
  # config.api_origin = nil

  # Merge your own dicionary with ErrorsSavior dictionary
  config.external_dictionary_errors_path = 'config/locales/gems/errors_savior'
  config.locale = :en
end

# config/locales/gems/errors_savior/en.yml

en:
  ArgumentError:
    error_code: 1010
    http_status_sym: unprocessable_entity
    http_status_code: 422
    message: 'One or more fields are invalid'

  MyCustomError:
    error_code: 2010
    http_status_sym: not_acceptable
    http_status_code: 404
    message: 'Custom error, error message'

  Pundit::NotAuthorizedError:
    error_code: 2020
    http_status_sym: unauthorized
    http_status_code: 401
    message: "User not allowed to perform that action"

  InvalidSchemaError:
    error_code: 2030
    http_status_sym: not_acceptable
    http_status_code: 404
    message: "Provided parameters doesn't validate with the expected schema"