simplest_dci_example.rb

class Account
  
  def initialize(id)
    @balance = 0
    @id      = id
  end

  def decrease_balance(amount)
    @balance -= amount
  end

  def increase_balance(amount)
    @balance += amount
  end

  def to_s
    "Account ##{@id} balance: #{@balance}"
  end

end

module ContextAccessor
  def context
    Thread.current[:context]
  end
  def context=(ctx)
    Thread.current[:context] = ctx
  end
  def execute_in_context
    old = self.context
    self.context = self
    yield
    self.context = old
  end
end

module MoneySourceRole
  
  include ContextAccessor

  def transfer_to
    # begin_transaction
    #raise "Insuffictent funds" if ...
    self.decrease_balance(context.amount)
    context.destination_account.transfer_from
    # log ...
    # end_transaction
  end
end

module MoneySinkRole
  
  include ContextAccessor

  def transfer_from
    self.increase_balance(context.amount)
    # log ...
  end
end

class MoneyTransferContext

  include ContextAccessor
  attr_accessor :source_account, :destination_account, :amount

  def initialize(source_id, destination_id, amount)
    
    self.source_account = Account.new(source_id)
    self.source_account.extend MoneySourceRole

    self.destination_account = Account.new(destination_id)
    self.destination_account.extend MoneySinkRole
    
    self.amount = amount
  end

  def perform
    execute_in_context { source_account.transfer_to }
    puts source_account
    puts destination_account
  end
end

context = MoneyTransferContext.new(1, 2, 100)
context.perform