// 这是一个典型的生产级"坏代码" —— 仅做演示，切勿复制到生产环境
if ($orderStatus == 'pending') {
    // 支付成功
    if ($paymentStatus == 'success') {
        $newStatus = 'paid';
        // 然后手动触发采购
        $this->purchaseSku($orderId);
    }
} elseif ($orderStatus == 'paid' && $logisticsService->hasPickUp()) {
    $newStatus = 'shipped';
} elseif ($orderStatus == 'paid' && $logisticsService->hasArrivedAtWarehouse()) {
    $newStatus = 'warehoused';
}
// ... 后面还有15个elseif分支

<?php

class OrderStateMachine
{
    private array $states;        // 所有合法的状态
    private array $transitions;   // 状态流转规则：[fromState => [toState1, toState2, ...]]
    private string $currentState; // 当前状态
    private int $orderId;         // 订单ID（用于数据库持久化）
    private array $transitionLog = []; // 状态变更日志

    /**
     * @param string $orderId订单ID
     * @param string $initialState初始状态
     */
    public function __construct(string $orderId, string $initialState = 'pending')
    {
        $this->orderId = $orderId;
        $this->currentState = $initialState;

        // 定义所有合法状态
        $this->states = [
            'pending',         // 待付款
            'cancelled',       // 已取消
            'paid',            // 已付款
            'purchasing',      // 1688代采中
            'purchased',       // 代采完成
            'warehoused',      // 已入库
            'inspected',       // 已验货
            'packed',          // 已合包
            'shipped',         // 已发货
            'delivered',       // 已签收
        ];

        // 定义严格的状态流转规则
        $this->transitions = [
            'pending' => ['paid', 'cancelled'],
            'paid' => ['purchasing', 'cancelled'], // 付款后可以取消但有成本
            'purchasing' => ['purchased', 'cancelled'],
            'purchased' => ['warehoused', 'cancelled'],
            'warehoused' => ['inspected', 'cancelled'],
            'inspected' => ['packed'],
            'packed' => ['shipped'],
            'shipped' => ['delivered'],
        ];
    }

    /**
     * 尝试执行状态转移
     * @param string $toState目标状态
     * @return bool
     * @throws RuntimeException如果转移不被允许
     */
    public function apply(string $toState): bool
    {
        // 1. 合法性验证
        if (!in_array($toState, $this->states, true)) {
            throw new RuntimeException("目标状态 {$toState} 非法");
        }

        // 2. 检查此转移是否被允许
        $allowedFrom = $this->transitions[$this->currentState] ?? [];
        if (!in_array($toState, $allowedFrom, true)) {
            $errorMsg = sprintf(
                "状态转移不被允许: %s -> %s, 当前仅允许: %s",
                $this->currentState,
                $toState,
                implode(', ', $allowedFrom)
            );
            throw new RuntimeException($errorMsg);
        }

        // 3. 添加前置条件检查（针对特定转移）
        $this->validatePreConditions($this->currentState, $toState);

        // 4. 执行转移：更新当前状态并写入日志
        $oldState = $this->currentState;
        $this->currentState = $toState;
        $this->transitionLog[] = [
            'timestamp' => date('Y-m-d H:i:s'),
            'from' => $oldState,
            'to' => $toState,
        ];

        // 5. 异步持久化到数据库（使用MySQL + Redis避免并发问题）
        $this->persistStatus($oldState, $toState);

        return true;
    }

    /**
     * 前置条件检查 —— 这里演示 "purchasing -> purchased" 需要校验1688接口返回
     */
    private function validatePreConditions(string $from, string $to): void
    {
        if ($from === 'purchasing' && $to === 'purchased') {
            // 模拟调用1688接口，检查采购结果
            $purchaseResult = PurchaseService::checkOrderStatus($this->orderId);
            if (!$purchaseResult['success']) {
                throw new RuntimeException(
                    "1688代采失败，前置校验不通过: " . ($purchaseResult['error'] ?? '未知错误')
                );
            }
        }

        if ($from === 'paid' && $to === 'cancelled') {
            // 已付款的订单取消，需要计算退款金额
            $this->initiateRefundProcess();
        }
    }

    /**
     * 数据库持久化：使用Redis分布式锁防止并发
     */
    private function persistStatus(string $oldState, string $newState): void
    {
        $lockKey = "order_lock_{$this->orderId}";
        $lock = RedisLock::acquire($lockKey, 10); // 10秒超时

        if (!$lock) {
            throw new RuntimeException("无法获取订单锁，状态更新可能冲突");
        }

        try {
            $db = Database::getInstance();
            $db->beginTransaction();

            // 更新主表状态
            $sql = "UPDATE `orders` SET `status` = :new_status WHERE `id` = :order_id AND `status` = :old_status";
            $stmt = $db->prepare($sql);
            $stmt->execute([
                ':new_status' => $newState,
                ':order_id' => $this->orderId,
                ':old_status' => $oldState,
            ]);

            if ($stmt->rowCount() === 0) {
                // 并发更新失败，说明其他进程已经改过状态
                $db->rollBack();
                throw new RuntimeException("并发更新失败，状态可能已经被其他进程修改");
            }

            // 插入日志表
            $logSql = "INSERT INTO `order_status_log` (`order_id`, `from_status`, `to_status`, `operator`, `created_at`) VALUES (?, ?, ?, ?, NOW())";
            $logStmt = $db->prepare($logSql);
            $logStmt->execute([$this->orderId, $oldState, $newState, 'system']);

            $db->commit();
        } catch (\Throwable $e) {
            $db->rollBack();
            throw $e;
        } finally {
            RedisLock::release($lockKey, $lock);
        }
    }

    /**
     * 获取当前状态
     */
    public function getCurrentState(): string
    {
        return $this->currentState;
    }

    /**
     * 获取状态变更日志
     */
    public function getTransitionLog(): array
    {
        return $this->transitionLog;
    }
}