<?php

namespace App\Module\Shop\Models;

use Illuminate\Database\Eloquent\Relations\BelongsTo;
use UCore\ModelCore;

/**
 * 商店促销商品关联模型
 *
 * field start 
 * @property  int  $id  关联ID，主键
 * @property  int  $promotion_id  促销ID，外键关联kku_shop_promotions表
 * @property  int  $shop_item_id  商品ID，外键关联kku_shop_items表
 * @property  int  $custom_discount_value  自定义折扣值（可为空，优先于促销活动的折扣值）
 * @property  \Carbon\Carbon  $created_at  创建时间
 * @property  \Carbon\Carbon  $updated_at  更新时间
 * field end
 */
class ShopPromotionItem extends ModelCore
{
    /**
     * 与模型关联的表名
     *
     * @var string
     */
    protected $table = 'shop_promotion_items';

    /**
     * 可批量赋值的属性
     *
     * @var array
     */
    protected $fillable = [
        'promotion_id',
        'shop_item_id',
        'custom_discount_value',
    ];

    /**
     * 获取关联的促销活动
     *
     * @return BelongsTo
     */
    public function promotion(): BelongsTo
    {
        return $this->belongsTo(ShopPromotion::class, 'promotion_id');
    }

    /**
     * 获取关联的商品
     *
     * @return BelongsTo
     */
    public function shopItem(): BelongsTo
    {
        return $this->belongsTo(ShopItem::class, 'shop_item_id');
    }

    /**
     * 计算折扣后的价格
     *
     * @return int|null 折扣后的价格，如果商品或促销活动不存在则返回null
     */
    public function getDiscountedPrice(): ?int
    {
        $shopItem = $this->shopItem;
        $promotion = $this->promotion;

        if (!$shopItem || !$promotion || !$promotion->isValid()) {
            return null;
        }

        return $promotion->calculateDiscountedPrice(
            $shopItem->price,
            $this->custom_discount_value
        );
    }
}