CallableService Concern for Rails

callable_service.rb

# Usually service classes have only one purpose and thus should have only one public method that triggers action
# This module simplifies the common approach:
#
#   SomeService.new(a, b, c).call
#
#    To:
#
#    SomeService.call(a, b, c)
#
# Requirements for class:
#
# 1. Have instance method #call
# 2. include CallableService
#
# Use cases:
#
# 1. Can be used instead of Sidekiq worker when worker just delegates to service
#    SomeService.delay.call(a, b, c)
#
# 2. Less code in specs when checking expectation that service was called
#
#    expect(SomeService).to receive(:call).with(a, b, c)
#
#    instead of:
#
#    service = double(SomeService)
#    expect(service).to receive(:call)
#    expect(SomeService).to receive(:new).with(a,b,c).and_return(service)
#
# 3. Can be used in maps
#
#  ['Check Up', 'Covid-19 Testing'].map(&StringFormatService)
#
#  instead of
#
#  ['Check Up', 'Covid-19 Testing'].map do |string|
#    StringFormatService.new(string).call
#  end
#
# 4. Can still be initiated with #new to debug inner state, like
#
#    service = SomeService.new(a,b,c)
#    service.send(:some_private_method)
#

module CallableService
  extend ActiveSupport::Concern

  module ClassMethods
    def call(*args, &block)
      new(*args, &block).call
    end

    def to_proc
      public_method(:call).to_proc
    end
  end
end