Decorators & Presenters

account_presenter.rb

class AccountPresenter
  extend Forwardable

  attr_reader :account

  def_delegators :account, :amount, :created_at

  def initialize(account)
    @account = account
  end

  def owner
    account.user.name
  end
end

account_presenter_test.rb

require 'test_helper'

class AccountPresenterTest < ActiveSupport::TestCase
  test 'it has an owner' do
    user              = User.create(name: 'Arya')
    account           = Account.create(amount: 500, user_id: user.id)
    account_presenter = AccountPresenter.new(account)

    assert_equal 'Arya', account_presenter.owner
  end
end

accounts_controller.rb

class AccountsController < ApplicationController
  def show
    @account = AccountPresenter.new(current_user.account)
  end
end

transfer_funds.rb

class TransferFunds
  extend Forwardable

  def self.create(params, user)
    self.new(params, user)
  end

  attr_reader :transfer, :user

  def_delegators :transfer, :amount, :id

  def initialize(params, user)
    @transfer = Transfer.create(params)
    @user     = user
  end

  def save
    if transfer.save && user.account.amount >= transfer.amount
      account        = user.account
      account.amount = (account.amount - transfer.amount)
      account.save
    end
  end
end

transfer_funds_test.rb

require 'test_helper'

class TransferFundsTest < ActiveSupport::TestCase
  test 'it creates' do
    user_1          = User.create(name: 'DJ')
    transfer_params = { amount: '1212', incoming_id: '3', outgoing_id: '1' }
    transfer        = TransferFunds.create(transfer_params, user_1)

    assert_equal TransferFunds, transfer.class
    assert Transfer.find_by(incoming_id: '3')
  end

  test 'it saves' do
    user_1           = User.create(name: 'DJ')
    user_2           = User.create(name: 'Miriam')
    outgoing_account = Account.create(amount: 1000, user_id: user_1.id)
    incoming_account = Account.create(amount: 1000, user_id: user_2.id)
    transfer_params  = { amount: 500, incoming_id: incoming_account.id, outgoing_id: outgoing_account.id }
    transfer         = TransferFunds.create(transfer_params, user_1)

    assert transfer.save
    assert_equal 500, user_1.account.amount
  end
end

transfers_controller.rb

class TransfersController < ApplicationController
  def index
    @transfers = current_user.transfers
  end

  def show
    @transfer = current_user.account.outgoing_transfers.find_by(id: params[:id])
  end

  def new
    @transfer = Transfer.new
  end

  def create
    @transfer = TransferFunds.create(transfer_params, current_user)

    if @transfer.save
      redirect_to transfer_path(id: @transfer.id), success: "Your transfer of #{@transfer.amount} dollars was successful."
    else
      flash.now[:warning] = 'Your transfer could not be completed. Please, try again.'
      render :new
    end
  end

  private

  def transfer_params
    params.require(:transfer).permit(:amount, :incoming_id, :outgoing_id)
  end
end