<?php

namespace App\Service\business;

use App\Models\business\PriceSheetModel;
use App\Service\common\UtilsService;

/**
 * 规格库存：stock=-1 表示不限，兼容历史数据全是不限。
 */
class StockService
{
    private static mixed $_instance;

    public static function getInstance(): null|static
    {
        $name = get_called_class();
        if (!isset(self::$_instance[$name])) {
            self::$_instance[$name] = new static();
        }
        return self::$_instance[$name];
    }

    /**
     * 加入清单 / 下单前校验。sheetId=0 时跳过（还没选规格）。
     */
    public function assertAvailable(int $sheetId, int $quantity): void
    {
        if ($sheetId <= 0) {
            return;
        }
        $sheet = PriceSheetModel::where('id', $sheetId)->where('deleted_at', 0)->first();
        if (empty($sheet)) {
            UtilsService::getInstance()->errorThrow('规格不存在');
        }
        $stock = (int) ($sheet['stock'] ?? -1);
        if ($stock < 0) {
            return;
        }
        if ($stock < $quantity) {
            UtilsService::getInstance()->errorThrow('库存不足（剩余 ' . $stock . '）');
        }
    }

    /**
     * 下单成功后扣库存；不限库存不写库。
     */
    public function deduct(int $sheetId, int $quantity): void
    {
        if ($sheetId <= 0 || $quantity <= 0) {
            return;
        }
        $sheet = PriceSheetModel::where('id', $sheetId)->where('deleted_at', 0)->first();
        if (empty($sheet)) {
            return;
        }
        $stock = (int) ($sheet['stock'] ?? -1);
        if ($stock < 0) {
            return;
        }
        $next = max(0, $stock - $quantity);
        PriceSheetModel::where('id', $sheetId)->update([
            'stock' => $next,
            'updated_at' => time(),
        ]);
    }
}