Rails generator for services and lib objects

generators-service-service_generator.rb

class ServiceGenerator < Rails::Generators::NamedBase
  argument :arguments, type: :array, default: [], banner: "argument argument"

  source_root File.expand_path('../templates', __FILE__)

  check_class_collision suffix: "Service"

  def create_service_files
    template "service.rb.tt", File.join("lib", class_path, "#{file_name}_service.rb")
    template(
      'service_spec.rb.tt',
      File.join('spec', 'lib', class_path, "#{file_name}_service_spec.rb"),
    )
  end

  private

  def file_name
    @_file_name ||= remove_possible_suffix(super)
  end

  def remove_possible_suffix(name)
    name.sub(/_?service$/i, "")
  end

  def class_name_without_module
    file_name.camelize
  end

  # Wrap block with `module` blocks.
  def module_namespacing(&block)
    content = capture(&block)
    class_path.reverse.each do |module_name|
      content = wrap_with_module(module_name, content)
    end
    concat(content)
  end

  def indent(content, multiplier = 2)
    spaces = " " * multiplier
    content.each_line.map { |line| line.blank? ? line : "#{spaces}#{line}" }.join
  end

  def wrap_with_module(module_name, content) # :doc:
    content = indent(content).chomp
    "module #{module_name.camelize}\n#{content}\nend\n"
  end
end

generators-service-templates-service.rb.tt

# frozen_string_literal: true

<% module_namespacing do -%>
class <%= class_name_without_module %>Service
  class SpecificErrorClass < StandardError; end

<%- if arguments.any? -%>
  def initialize(<%= arguments.map { |argument| "#{argument}:" }.join(', ') %>)
  <%- for argument in arguments -%>
    @<%= argument %> = <%= argument %>
  <%- end -%>
  end

<%- end -%>
  def run!
    raise SpecificErrorClass, "TODO: Implement this."
  end

  def run
    run!
    true
  rescue SpecificErrorClass
    false
  end

  private

<%- for argument in arguments -%>
  attr_reader :<%= argument %>
<%- end -%>
end
<% end -%>

generators-service-templates-service_spec.rb.tt

# frozen_string_literal: true

require 'rails_helper'

RSpec.describe <%= class_name %>Service do
<%- if arguments.empty? -%>
  let(:service) { described_class.new }
<%- else -%>
  let(:service) {
    described_class.new(
  <%- for argument in arguments -%>
      <%= argument %>: <%= argument %>,
  <%- end -%>
    )
  }
  <%- for argument in arguments -%>
  let(:<%= argument %>) { nil }
  <%- end -%>
<%- end -%>

  before do
    pending "TODO: Implement these specs and remove this `before` block."
  end

  describe '#run!' do
    subject(:run!) { service.run! }

    context 'when things go well' do
      it 'does something'
    end

    context 'when things go wrong' do
      it 'raises an error' do
        expect { run! }.to raise_error(<%= class_name %>Service::SpecificErrorClass)
      end
    end
  end

  describe '#run' do
    subject(:run) { service.run }

    context 'when things go well' do
      it 'returns true' do
        expect(run).to be_truthy
      end
    end

    context 'when things go wrong' do
      it 'returns false' do
        expect(run).to be_falsey
      end
    end
  end
end

generators-service-USAGE

Description:
    Stubs a new Service object in the `lib` folder and a spec for it.

    Providing a list of argument names will set up the initializer to accept them
    and create private accessors for each of them.

    To create a service within a module, specify the service name as a
    path like 'parent_module/service_name' or 'ParentModule::ServiceName'.

Example:
    rails generate service ParentModule::Thing foo bar

    This will create:
        Service: lib/parent_module/thing_service.rb
        Spec:    spec/lib/parent_module/thing_service_spec.rb