# Laravel 课时消耗系统设计

针对学生课时消耗的需求，我建议采用以下设计方案：

## 核心设计思路

1. **订单与课时消耗解耦**：通过中间表记录课时消耗情况
2. **消耗顺序**：先消耗购买课时，再消耗赠送课时
3. **撤销功能**：记录每次消耗的日志，便于撤销
4. **多订单处理**：按订单创建时间顺序处理

## 数据库设计

```php
// 订单表
Schema::create('orders', function (Blueprint $table) {
    $table->id();
    $table->unsignedBigInteger('student_id');
    $table->integer('paid_lessons'); // 购买课时
    $table->integer('free_lessons');  // 赠送课时
    $table->integer('remaining_paid_lessons'); // 剩余购买课时
    $table->integer('remaining_free_lessons'); // 剩余赠送课时
    $table->timestamps();

    $table->foreign('student_id')->references('id')->on('students');
});

// 课时消耗记录表
Schema::create('lesson_consumptions', function (Blueprint $table) {
    $table->id();
    $table->unsignedBigInteger('student_id');
    $table->unsignedBigInteger('order_id')->nullable();
    $table->integer('amount'); // 消耗数量
    $table->enum('type', ['paid', 'free']); // 消耗类型
    $table->string('description'); // 消耗描述
    $table->boolean('is_reversed')->default(false); // 是否已撤销
    $table->timestamps();

    $table->foreign('student_id')->references('id')->on('students');
    $table->foreign('order_id')->references('id')->on('orders');
});
```

## 服务类实现

```php
namespace App\Services;

use App\Models\Order;
use App\Models\LessonConsumption;
use Illuminate\Support\Facades\DB;

class LessonConsumptionService
{
    /**
     * 消耗课时
     */
    public function consumeLessons($studentId, $amount, $description)
    {
        return DB::transaction(function () use ($studentId, $amount, $description) {
            $remainingAmount = $amount;
            $orders = Order::where('student_id', $studentId)
                ->where(function ($query) {
                    $query->where('remaining_paid_lessons', '>', 0)
                          ->orWhere('remaining_free_lessons', '>', 0);
                })
                ->orderBy('created_at')
                ->lockForUpdate()
                ->get();

            $consumptions = [];

            foreach ($orders as $order) {
                if ($remainingAmount <= 0) break;

                // 先消耗购买课时
                if ($order->remaining_paid_lessons > 0) {
                    $consumed = min($remainingAmount, $order->remaining_paid_lessons);

                    $consumptions[] = $this->createConsumption(
                        $studentId,
                        $order->id,
                        $consumed,
                        'paid',
                        $description
                    );

                    $order->decrement('remaining_paid_lessons', $consumed);
                    $remainingAmount -= $consumed;
                }

                // 再消耗赠送课时
                if ($remainingAmount > 0 && $order->remaining_free_lessons > 0) {
                    $consumed = min($remainingAmount, $order->remaining_free_lessons);

                    $consumptions[] = $this->createConsumption(
                        $studentId,
                        $order->id,
                        $consumed,
                        'free',
                        $description
                    );

                    $order->decrement('remaining_free_lessons', $consumed);
                    $remainingAmount -= $consumed;
                }
            }

            if ($remainingAmount > 0) {
                throw new \Exception("课时不足，还缺少 {$remainingAmount} 课时");
            }

            return $consumptions;
        });
    }

    /**
     * 创建消耗记录
     */
    protected function createConsumption($studentId, $orderId, $amount, $type, $description)
    {
        return LessonConsumption::create([
            'student_id' => $studentId,
            'order_id' => $orderId,
            'amount' => $amount,
            'type' => $type,
            'description' => $description,
        ]);
    }

    /**
     * 撤销课时消耗
     */
    public function reverseConsumption($consumptionId)
    {
        return DB::transaction(function () use ($consumptionId) {
            $consumption = LessonConsumption::lockForUpdate()->findOrFail($consumptionId);

            if ($consumption->is_reversed) {
                throw new \Exception('该消耗记录已撤销');
            }

            // 恢复订单中的课时
            if ($consumption->order_id) {
                $order = Order::lockForUpdate()->find($consumption->order_id);

                if ($consumption->type === 'paid') {
                    $order->increment('remaining_paid_lessons', $consumption->amount);
                } else {
                    $order->increment('remaining_free_lessons', $consumption->amount);
                }
            }

            // 标记为已撤销
            $consumption->update(['is_reversed' => true]);

            return $consumption;
        });
    }
}
```

## 使用示例

```php
// 消耗课时
$service = new LessonConsumptionService();
try {
    $consumptions = $service->consumeLessons($studentId, 3, '常规课程消耗');
    // 处理成功
} catch (\Exception $e) {
    // 处理失败
}

// 撤销消耗
try {
    $reversed = $service->reverseConsumption($consumptionId);
    // 撤销成功
} catch (\Exception $e) {
    // 撤销失败
}
```

## 设计优势

1. **解耦设计**：课时消耗记录与订单分离，便于管理和查询
2. **事务处理**：使用数据库事务确保数据一致性
3. **撤销功能**：通过记录消耗日志实现撤销
4. **消耗顺序**：严格按照先购买后赠送的顺序消耗
5. **并发安全**：使用锁机制防止并发问题

## 扩展考虑

1. 可以添加课时消耗事件，便于后续业务扩展
2. 可以添加课时余额快照功能，便于历史查询
3. 可以添加课时有效期管理，自动过期处理

这个设计提供了灵活且可靠的课时管理系统，满足您的需求同时保持了良好的扩展性。