mark_receipt_paid.rb

class MarkReceiptPaid < ActiveInteraction::Base
  # Required Params
  #----------------------------------------------------------------------------
  model :receipt

  # Validations
  #----------------------------------------------------------------------------
  validates :receipt, :presence => true

  # Execution
  #----------------------------------------------------------------------------
  def execute
    if receipt.paid?
      errors.add(:receipt, :already_paid)
    else
      create_reimbursement
      mark_paid
      receipt
    end
  end

  # Private Methods
  #----------------------------------------------------------------------------
  private
  def reimbursable_amount
    receipt.amount
  end

  def mark_paid
    receipt.paid_at = Time.zone.now
    receipt.mark_paid
  end

  def create_reimbursement
    receipt.build_reimbursement.tap do |r|
      r.amount = reimbursable_amount
      r.save!
    end
  end
end

receipts_controller.rb

class ReceiptsController < ApplicationController
  # GET /customer/receipts
  #-------------------------------------------------------------------
  def index
    render action: :index, locals: { receipts: Receipt.all }
  end

  # PUT /customer/receipts/1/mark_paid
  #-------------------------------------------------------------------
  def mark_paid
    outcome = MarkReceiptPaid.run(receipt: unpaid_receipt)
    if outcome.valid?
      marked_paid
    else
      reimbursement_invalid
    end
  end

  def marked_paid
    flash[:alert] = "Marked as paid."
    redirect_to action: :index
  end

  def reimbursement_invalid
    flash[:alert] = "Error."
    render action: :index
  end

private
  def unpaid_receipt
    Receipt.unpaid.find(params[:id]) || (raise Exceptions::AccessDenied)
  end
end