Memento Pattern in Swift

memento-pattern.swift

/*
Memento Pattern
1. The `originator` is the object to be saved or restored.
2. The `memento` represents a stored state.
3. The `caretaker` requests a save from the originator and receives a memento in response. 
The caretaker is responsible for persisting the memento and, later on, 
providing the memento back to the originator to restore the originator’s state.
*/

protocol Originator {
    func save() -> Memento
    func restore(memento: Memento)
}

class BankAccount: Originator {
    private(set) var balance: Double = 0.0

    func setBalance(balance: Double) {
        self.balance = balance
    }

    func save() -> Memento {
        return Memento(balance: balance)
    }

    func restore(memento: Memento) {
        balance = memento.balance
    }
}

class Memento {
    let balance: Double

    init(balance: Double) {
        self.balance = balance
    }
}

// Care Taker
class BankCustomer {
    let account: BankAccount

    init(account: BankAccount) {
        self.account = account
    }

    func withdraw(amount: Double) {
        let memento = account.save()
        account.setBalance(balance: account.balance - amount)
        if account.balance < 0 {
            account.restore(memento: memento)
            print("Insufficient funds.")
        }
    }

    func deposit(amount: Double) {
        account.setBalance(balance: account.balance + amount)
    }
}

let account = BankAccount()
let customer = BankCustomer(account: account)
print("Balance: \(customer.account.balance)")

print("\nDeposit 100")
customer.deposit(amount: 100)
print("Balance: \(customer.account.balance)")

print("\nWithdraw 50")
customer.withdraw(amount: 50)
print("Balance: \(customer.account.balance)")

print("\nWithdraw 100")
customer.withdraw(amount: 100)
print("Balance: \(customer.account.balance)")

/*
Balance: 0.0

Deposit 100
Balance: 100.0

Withdraw 50
Balance: 50.0

Withdraw 100
Insufficient funds.
Balance: 50.0
*/