<?php
namespace App\Modules\Inventory\Services;

use App\Modules\Inventory\Models\Inventory;
use App\Modules\Inventory\Models\InventoryCountDoc;
use App\Modules\Inventory\Models\InventoryAdjustDoc;
use App\Modules\Inventory\Models\InventoryAdjustItem;
use Illuminate\Support\Facades\DB;

class AdjustService
{
    public function createDoc(string $warehouseId, string $reason, ?string $remarks = null, int $userId, ?int $countDocId = null): InventoryAdjustDoc
    {
        return InventoryAdjustDoc::create([
            'warehouse_id' => $warehouseId,
            'count_doc_id' => $countDocId,
            'status' => 'draft',
            'reason' => $reason,
            'remarks' => $remarks,
            'created_by' => $userId,
        ]);
    }

    /**
     * 從盤點單建立盤調單
     */
    public function createFromCountDoc(InventoryCountDoc $countDoc, int $userId): InventoryAdjustDoc
    {
        return DB::transaction(function () use ($countDoc, $userId) {
            // 1. 建立盤調單頭
            $adjDoc = $this->createDoc(
                $countDoc->warehouse_id,
                "盤點調整: " . $countDoc->doc_no,
                "由盤點單 {$countDoc->doc_no} 自動生成",
                $userId,
                $countDoc->id
            );

            // 2. 抓取有差異的明細 (diff_qty != 0)
            foreach ($countDoc->items as $item) {
                if (abs($item->diff_qty) < 0.0001) continue;

                $adjDoc->items()->create([
                    'product_id' => $item->product_id,
                    'batch_number' => $item->batch_number,
                    'qty_before' => $item->system_qty,
                    'adjust_qty' => $item->diff_qty,
                    'notes' => "盤點差異: " . $item->diff_qty,
                ]);
            }

            return $adjDoc;
        });
    }

    /**
     * 更新調整單內容 (Items)
     * 此處採用 "全量更新" 方式處理 items (先刪後加)，簡單可靠
     */
    public function updateItems(InventoryAdjustDoc $doc, array $itemsData): void
    {
        DB::transaction(function () use ($doc, $itemsData) {
            $doc->items()->delete();

            foreach ($itemsData as $data) {
                // 取得當前庫存作為 qty_before 參考 (僅參考，實際扣減以過帳當下為準)
                $inventory = Inventory::where('warehouse_id', $doc->warehouse_id)
                    ->where('product_id', $data['product_id'])
                    ->where('batch_number', $data['batch_number'] ?? null)
                    ->first();
                
                $qtyBefore = $inventory ? $inventory->quantity : 0;

                $doc->items()->create([
                    'product_id' => $data['product_id'],
                    'batch_number' => $data['batch_number'] ?? null,
                    'qty_before' => $qtyBefore,
                    'adjust_qty' => $data['adjust_qty'],
                    'notes' => $data['notes'] ?? null,
                ]);
            }
        });
    }

    /**
     * 過帳 (Post) - 生效庫存異動
     */
    public function post(InventoryAdjustDoc $doc, int $userId): void
    {
        DB::transaction(function () use ($doc, $userId) {
            foreach ($doc->items as $item) {
                if ($item->adjust_qty == 0) continue;

                // 找尋或建立 Inventory
                // 若是減少庫存，必須確保 Inventory 存在 (且理論上不能變負? 視策略而定，這裡假設允許變負或由 InventoryService 控管)
                // 若是增加庫存，若不存在需建立
                
                $inventory = Inventory::firstOrNew([
                    'warehouse_id' => $doc->warehouse_id,
                    'product_id' => $item->product_id,
                    'batch_number' => $item->batch_number,
                ]);

                // 如果是新建立的 object (id 為空)，需要初始化 default
                if (!$inventory->exists) {
                     // 繼承 Product 成本或預設 0 (簡化處理)
                     $inventory->unit_cost = $item->product->cost ?? 0;
                     $inventory->quantity = 0; 
                }

                $oldQty = $inventory->quantity;
                $newQty = $oldQty + $item->adjust_qty;
                
                $inventory->quantity = $newQty;
                // 用最新的數量 * 單位成本 (簡化成本計算，不採用移動加權)
                $inventory->total_value = $newQty * $inventory->unit_cost;
                $inventory->save();

                // 建立 Transaction
                $inventory->transactions()->create([
                    'type' => '庫存調整',
                    'quantity' => $item->adjust_qty,
                    'unit_cost' => $inventory->unit_cost,
                    'balance_before' => $oldQty,
                    'balance_after' => $newQty,
                    'reason' => "調整單 {$doc->doc_no}: " . ($doc->reason ?? '手動調整'),
                    'actual_time' => now(),
                    'user_id' => $userId,
                ]);
            }

            $doc->update([
                'status' => 'posted',
                'posted_at' => now(),
                'posted_by' => $userId,
            ]);
        });
    }
    
    /**
     * 作廢 (Void)
     */
    public function void(InventoryAdjustDoc $doc, int $userId): void 
    {
         if ($doc->status !== 'draft') {
             throw new \Exception('只能作廢草稿狀態的單據');
         }
         $doc->update([
             'status' => 'voided',
             'updated_by' => $userId
         ]);
    }
}