实现一个订单处理流程。

流程：
```
创建订单
计算商品总价
应用优惠规则
校验库存
支付订单
扣减库存
发送订单确认通知
记录日志
```
要求使用：
```
OOP：订单、商品、库存、支付服务
策略模式：不同支付方式
函数式：优惠规则组合
事件驱动：支付成功后通知和日志
声明式：订单状态流转配置
```
练习点：
```
复杂业务建模
多范式协作
服务分层
事件系统
状态机
```

最后这道题综合使用 OOP、策略模式、函数式优惠、事件驱动和状态机。

代码
```
<?php

/**
 * 商品
 */
class Product
{
    public function __construct(
        public int $id,
        public string $name,
        public float $price,
        public int $stock
    ) {}
}

/**
 * 订单项
 */
class OrderItem
{
    public function __construct(
        public Product $product,
        public int $quantity
    ) {}

public function subtotal(): float
    {
        return $this->product->price * $this->quantity;
    }
}

/**
 * 订单
 */
class EcommerceOrder
{
    /**
     * @param OrderItem[] $items
     */
    public function __construct(
        public int $id,
        public array $items,
        public string $status = 'pending'
    ) {}

public function total(): float
    {
        return array_reduce(
            $this->items,
            fn(float $sum, OrderItem $item) => $sum + $item->subtotal(),
            0
        );
    }
}

/**
 * 支付接口
 */
interface EcommercePayment
{
    public function pay(float $amount): bool;
}

/**
 * 支付宝支付
 */
class EcommerceAlipay implements EcommercePayment
{
    public function pay(float $amount): bool
    {
        echo "支付宝支付：{$amount}" . PHP_EOL;
        return true;
    }
}

/**
 * 微信支付
 */
class EcommerceWeChatPay implements EcommercePayment
{
    public function pay(float $amount): bool
    {
        echo "微信支付：{$amount}" . PHP_EOL;
        return true;
    }
}

/**
 * 库存服务
 */
class InventoryService
{
    public function check(EcommerceOrder $order): bool
    {
        foreach ($order->items as $item) {
            if ($item->product->stock < $item->quantity) {
                return false;
            }
        }

return true;
    }

public function deduct(EcommerceOrder $order): void
    {
        foreach ($order->items as $item) {
            $item->product->stock -= $item->quantity;
        }
    }
}

/**
 * 电商事件调度器
 */
class EcommerceEventDispatcher
{
    private array $listeners = [];

public function listen(string $eventClass, callable $listener): void
    {
        $this->listeners[$eventClass][] = $listener;
    }

public function dispatch(object $event): void
    {
        foreach ($this->listeners[$event::class] ?? [] as $listener) {
            $listener($event);
        }
    }
}

/**
 * 支付成功事件
 */
class OrderPaid
{
    public function __construct(
        public EcommerceOrder $order,
        public float $amount
    ) {}
}

/**
 * 订单状态机
 */
class EcommerceOrderStateMachine
{
    private array $transitions = [
        'pending' => ['paid', 'cancelled'],
        'paid' => ['shipped'],
        'shipped' => ['completed'],
        'completed' => [],
        'cancelled' => [],
    ];

public function transition(EcommerceOrder $order, string $to): void
    {
        $from = $order->status;

if (!in_array($to, $this->transitions[$from] ?? [], true)) {
            throw new RuntimeException("非法状态流转：{$from} -> {$to}");
        }

$order->status = $to;
    }
}

/**
 * 优惠规则应用器
 */
function applyEcommerceDiscounts(float $amount, array $rules): float
{
    return array_reduce(
        $rules,
        fn(float $current, callable $rule) => $rule($current),
        $amount
    );
}

/**
 * 订单处理服务
 */
class OrderProcessor
{
    public function __construct(
        private InventoryService $inventory,
        private EcommerceOrderStateMachine $stateMachine,
        private EcommerceEventDispatcher $dispatcher
    ) {}

public function process(
        EcommerceOrder $order,
        EcommercePayment $payment,
        array $discountRules
    ): void {
        // 1. 校验库存
        if (!$this->inventory->check($order)) {
            throw new RuntimeException('库存不足');
        }

// 2. 计算总价
        $total = $order->total();

// 3. 应用优惠规则
        $finalAmount = applyEcommerceDiscounts($total, $discountRules);

// 4. 支付
        if (!$payment->pay($finalAmount)) {
            throw new RuntimeException('支付失败');
        }

// 5. 状态切换
        $this->stateMachine->transition($order, 'paid');

// 6. 扣减库存
        $this->inventory->deduct($order);

// 7. 触发支付成功事件
        $this->dispatcher->dispatch(new OrderPaid($order, $finalAmount));
    }
}

$product1 = new Product(1, 'Keyboard', 299, 10);
$product2 = new Product(2, 'Monitor', 1299, 5);

$order = new EcommerceOrder(1, [
    new OrderItem($product1, 1),
    new OrderItem($product2, 1),
]);

$discountRules = [
    fn(float $amount) => $amount >= 1000 ? $amount - 100 : $amount,
    fn(float $amount) => $amount * 0.9,
];

$dispatcher = new EcommerceEventDispatcher();

$dispatcher->listen(OrderPaid::class, function (OrderPaid $event) {
    echo "发送订单确认通知，订单 ID：" . $event->order->id . PHP_EOL;
});

$dispatcher->listen(OrderPaid::class, function (OrderPaid $event) {
    echo "记录支付日志，金额：" . $event->amount . PHP_EOL;
});

$processor = new OrderProcessor(
    new InventoryService(),
    new EcommerceOrderStateMachine(),
    $dispatcher
);

$processor->process($order, new EcommerceAlipay(), $discountRules);

echo "订单状态：" . $order->status . PHP_EOL;
echo "商品库存：" . $product1->stock . ', ' . $product2->stock . PHP_EOL;
```

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