一天一个设计模式（12）——责任链模式

<?php
abstract class Account {
    public $next;
    public $balance;
    public function setNext(Account $account) {
        $this->next = $account;
    }
    public function canPay($amount) {
        return $this->balance >= $amount;
    }
    public function pay($amount) {
        if ($this->canPay($amount)) {
            echo 'Paying ' . $amount . ' using ' . get_called_class() . PHP_EOL;
        } elseif ($this->next) {
            $this->next->pay($amount);
        } else {
            throw new Exception("Can not pay");
        }
    }
}

class PayA extends Account {
    public function __construct($balance) {
        $this->balance = $balance;
    }
}

class PayB extends Account {
    public function __construct($balance) {
        $this->balance = $balance;
    }
}

class PayC extends Account {
    public function __construct($balance) {
        $this->balance = $balance;
    }
}

$payA = new PayA(100);
$payB = new PayB(200);
$payC = new PayC(300);
$payA->setNext($payB);
$payB->setNext($payC);

$payA->pay(259);