<?php

namespace App\Services;

use App\Exceptions\RepositoryException;
use App\Models\PurchaseAllocationModel;
use App\Models\PurchaseOrderItemModel;
use App\Models\PurchaseOrderModel;
use App\Models\StoreOrderItemModel;
use App\Models\StoreOrderModel;
use Illuminate\Support\Facades\DB;

/**
 * D3 采购金额分摊
 *
 * 流程（事务内）：
 * 1. 采购单须已录入实际金额（存在 amount>0 的明细），否则拒绝
 * 2. 每个采购明细溯源「采购日当天、已汇总订单」中该商品的订货明细
 * 3. 按订货数量比例分摊实际金额/数量/重量：bcmul(item.amount, bcdiv(item_qty, total_qty, 6), 2)
 *    尾差修正——最后一行承担舍入差额，保证 Σallocation.amount === item.amount（金额守恒）
 * 4. 重复分摊先删旧记录再重建（幂等）
 */
class PurchaseAllocateService
{
    /**
     * @return int 生成的分摊记录数
     */
    public function allocate(PurchaseOrderModel $purchase): int
    {
        return DB::transaction(function () use ($purchase) {
            $items = PurchaseOrderItemModel::query()
                ->where('purchase_id', $purchase->id)
                ->lockForUpdate()
                ->get();

            // 1. 须已录入实际金额
            if (! $items->contains(static fn ($item) => (float) $item->amount > 0)) {
                throw new RepositoryException('采购单尚未录入实际金额，无法分摊');
            }

            // 2. 溯源采购日当天「已汇总」订单的订货明细，按商品分组
            $orderItems = StoreOrderItemModel::query()
                ->join('store_order', 'store_order.id', '=', 'store_order_item.order_id')
                ->whereDate('store_order.order_date', $purchase->purchase_date)
                ->where('store_order.status', StoreOrderModel::STATUS_SUMMARIZED)
                ->select('store_order_item.*')
                ->get()
                ->groupBy('product_id');

            // 4. 幂等：删除旧分摊记录
            PurchaseAllocationModel::query()
                ->whereIn('purchase_item_id', $items->pluck('id'))
                ->delete();

            $count = 0;
            $now = now();
            foreach ($items as $item) {
                $sources = $orderItems->get((int) $item->product_id);
                if ($sources === null || $sources->isEmpty()) {
                    continue;
                }

                $totalQty = $sources->reduce(
                    static fn (string $carry, $orderItem): string => bcadd($carry, (string) $orderItem->quantity, 2),
                    '0'
                );
                if ((float) $totalQty <= 0) {
                    continue;
                }

                $sourceValues = $sources->values();
                $lastIndex = $sourceValues->count() - 1;
                $allocatedAmount = '0';
                $allocatedQuantity = '0';
                $allocatedWeight = '0';
                $records = [];

                foreach ($sourceValues as $index => $orderItem) {
                    if ($index === $lastIndex) {
                        // 3. 尾差修正：最后一行 = 总额 − 已分摊，保证守恒
                        $amount = bcsub((string) $item->amount, $allocatedAmount, 2);
                        $quantity = bcsub((string) $item->quantity, $allocatedQuantity, 2);
                        $weight = bcsub((string) $item->weight, $allocatedWeight, 3);
                    } else {
                        $ratio = bcdiv((string) $orderItem->quantity, $totalQty, 6);
                        $amount = bcmul((string) $item->amount, $ratio, 2);
                        $quantity = bcmul((string) $item->quantity, $ratio, 2);
                        $weight = bcmul((string) $item->weight, $ratio, 3);
                        $allocatedAmount = bcadd($allocatedAmount, $amount, 2);
                        $allocatedQuantity = bcadd($allocatedQuantity, $quantity, 2);
                        $allocatedWeight = bcadd($allocatedWeight, $weight, 3);
                    }

                    $records[] = [
                        'purchase_item_id' => $item->id,
                        'order_item_id' => $orderItem->id,
                        'store_id' => $orderItem->store_id,
                        'product_id' => $item->product_id,
                        'quantity' => $quantity,
                        'weight' => $weight,
                        'amount' => $amount,
                        'created_at' => $now,
                        'updated_at' => $now,
                    ];
                }

                PurchaseAllocationModel::insert($records);
                $count += count($records);
            }

            return $count;
        });
    }
}