Bank Maker-Checker Refactoring (C#)

1_README.md

Bank Maker-Checker Refactoring (C#)

ApprovalStrategy.cs

namespace Bank {
  public abstract class ApprovalStrategy {
    public abstract bool Approve(Transactions transactions);

    public static ApprovalStrategy ValueOf(Transactions transactions) {
      if (transactions.TotalValue() < 100000)
        return new SingleMakerChecker(new Maker(), new Checker());
      else
        return new DoubleMakerChecker(new Maker(), 
                                      new Checker(), new Checker());
    }
  }

  public class SingleMakerChecker : ApprovalStrategy {
    public SingleMakerChecker(Maker m, Checker c) { }

    public override bool Approve(Transactions ts) {
      return true;
    }
  }

  public class DoubleMakerChecker : ApprovalStrategy {
    public DoubleMakerChecker(Maker m, Checker c1, Checker c2) { }

    public override bool Approve(Transactions ts) {
      return true;
    }
  }  
}

Domain.cs

namespace Bank {
  public class Maker { }

  public class Checker { }
  
  public interface Transaction { 
    bool Approve();
    bool Reject(String reason);
  }

  public class Debit : Transaction {
    public bool Approve() { return true; }
    public bool Reject(String reason) { return false; }
  }
  
  public class Credit : Transaction {
    public bool Approve() { return true; }
    public bool Reject(String reason) { return false; }
  }

  public class Transactions {
     private List<Transaction> transactions;

     public Transactions(List<Transaction> transactions) { 
       this.transactions = transactions;
     }

     public bool Approve(ApprovalStrategy aps) {
       return aps.Approve(this);
     } 

     public double TotalValue() { 
       // This is hard-coded for purpose of this example.
       return 1000000d; 
     }  
  }
}

Main.cs

using System;
using System.Collections;
using System.Collections.Generic;
using Bank;

public class Main {
  public static List<Transaction> CreateTransactions() {
    return new List<Transaction> { new Debit(), new Credit() };
  }

  public static void Main(String[] args) {
    Transactions transactions = new Transactions(CreateTransactions());
    ApprovalStrategy approvalStrategy = ApprovalStrategy.ValueOf(transactions);
    Console.WriteLine(transactions.Approve(approvalStrategy)); // True
  }
}