<?php

namespace App\Modules\Inventory\Services;

use App\Modules\Inventory\Contracts\InventoryServiceInterface;
use App\Modules\Inventory\Models\Inventory;
use App\Modules\Inventory\Models\Warehouse;
use App\Modules\Inventory\Models\Product;
use Illuminate\Support\Facades\DB;

class InventoryService implements InventoryServiceInterface
{
    public function getAllWarehouses()
    {
        return Warehouse::all();
    }

    public function getAllProducts()
    {
        return Product::with(['baseUnit', 'largeUnit'])->get();
    }

    public function getUnits()
    {
        return \App\Modules\Inventory\Models\Unit::all();
    }

    public function getInventoriesByIds(array $ids, array $with = [])
    {
        return Inventory::whereIn('id', $ids)->with($with)->get();
    }

    public function getProduct(int $id)
    {
        return Product::with(['baseUnit', 'largeUnit'])->find($id);
    }

    public function getProductsByIds(array $ids)
    {
        return Product::whereIn('id', $ids)->with(['baseUnit', 'largeUnit'])->get();
    }

    public function getProductsByName(string $name)
    {
        return Product::where('name', 'like', "%{$name}%")->with(['baseUnit', 'largeUnit'])->get();
    }

    public function getWarehouse(int $id)
    {
        return Warehouse::find($id);
    }

    public function checkStock(int $productId, int $warehouseId, float $quantity): bool
    {
        $stock = Inventory::where('product_id', $productId)
            ->where('warehouse_id', $warehouseId)
            ->sum('quantity');
            
        return $stock >= $quantity;
    }

    public function decreaseStock(int $productId, int $warehouseId, float $quantity, ?string $reason = null): void
    {
        DB::transaction(function () use ($productId, $warehouseId, $quantity, $reason) {
            $inventories = Inventory::where('product_id', $productId)
                ->where('warehouse_id', $warehouseId)
                ->where('quantity', '>', 0)
                ->orderBy('arrival_date', 'asc')
                ->get();

            $remainingToDecrease = $quantity;

            foreach ($inventories as $inventory) {
                if ($remainingToDecrease <= 0) break;

                $decreaseAmount = min($inventory->quantity, $remainingToDecrease);
                $this->decreaseInventoryQuantity($inventory->id, $decreaseAmount, $reason);
                $remainingToDecrease -= $decreaseAmount;
            }

            if ($remainingToDecrease > 0) {
                // 這裡可以選擇報錯或允許負庫存，目前為了嚴謹拋出異常
                throw new \Exception("庫存不足，無法扣除所有請求的數量。");
            }
        });
    }

    public function getInventoriesByWarehouse(int $warehouseId)
    {
        return Inventory::with(['product.baseUnit', 'product.largeUnit'])
            ->where('warehouse_id', $warehouseId)
            ->where('quantity', '>', 0)
            ->orderBy('arrival_date', 'asc')
            ->get();
    }

    public function createInventoryRecord(array $data)
    {
        return DB::transaction(function () use ($data) {
            // 嘗試查找是否已有相同批號的庫存
            $inventory = Inventory::where('warehouse_id', $data['warehouse_id'])
                ->where('product_id', $data['product_id'])
                ->where('batch_number', $data['batch_number'] ?? null)
                ->first();

            $balanceBefore = 0;

            if ($inventory) {
                // 若存在，則更新數量與相關資訊 (鎖定行以避免併發問題)
                $inventory = Inventory::lockForUpdate()->find($inventory->id);
                $balanceBefore = $inventory->quantity;
                
                // 加權平均成本計算 (可選，這裡先採簡單邏輯：若有新成本則更新，否則沿用)
                // 若本次入庫有指定成本，則更新該批次單價 (假設同批號成本相同)
                if (isset($data['unit_cost'])) {
                    $inventory->unit_cost = $data['unit_cost'];
                }
                
                $inventory->quantity += $data['quantity'];
                // 更新總價值
                $inventory->total_value = $inventory->quantity * $inventory->unit_cost;

                // 更新其他可能變更的欄位 (如最後入庫日)
                $inventory->arrival_date = $data['arrival_date'] ?? $inventory->arrival_date;
                $inventory->save();
            } else {
                // 若不存在，則建立新紀錄
                $unitCost = $data['unit_cost'] ?? 0;
                $inventory = Inventory::create([
                    'warehouse_id' => $data['warehouse_id'],
                    'product_id' => $data['product_id'],
                    'quantity' => $data['quantity'],
                    'unit_cost' => $unitCost,
                    'total_value' => $data['quantity'] * $unitCost,
                    'batch_number' => $data['batch_number'] ?? null,
                    'box_number' => $data['box_number'] ?? null,
                    'origin_country' => $data['origin_country'] ?? 'TW',
                    'arrival_date' => $data['arrival_date'] ?? now(),
                    'expiry_date' => $data['expiry_date'] ?? null,
                    'quality_status' => $data['quality_status'] ?? 'normal',
                    'source_purchase_order_id' => $data['source_purchase_order_id'] ?? null,
                ]);
            }

            \App\Modules\Inventory\Models\InventoryTransaction::create([
                'inventory_id' => $inventory->id,
                'type' => '入庫',
                'quantity' => $data['quantity'],
                'unit_cost' => $inventory->unit_cost, // 記錄當下成本
                'balance_before' => $balanceBefore,
                'balance_after' => $inventory->quantity,
                'reason' => $data['reason'] ?? '手動入庫',
                'reference_type' => $data['reference_type'] ?? null,
                'reference_id' => $data['reference_id'] ?? null,
                'user_id' => auth()->id(),
                'actual_time' => now(),
            ]);

            return $inventory;
        });
    }

    public function decreaseInventoryQuantity(int $inventoryId, float $quantity, ?string $reason = null, ?string $referenceType = null, $referenceId = null): void
    {
        DB::transaction(function () use ($inventoryId, $quantity, $reason, $referenceType, $referenceId) {
            $inventory = Inventory::lockForUpdate()->findOrFail($inventoryId);
            $balanceBefore = $inventory->quantity;
            
            $inventory->decrement('quantity', $quantity); // decrement 不會自動觸發 total_value 更新
            // 需要手動更新總價值
            $inventory->refresh();
            $inventory->total_value = $inventory->quantity * $inventory->unit_cost;
            $inventory->save();

            \App\Modules\Inventory\Models\InventoryTransaction::create([
                'inventory_id' => $inventory->id,
                'type' => '出庫',
                'quantity' => -$quantity,
                'unit_cost' => $inventory->unit_cost, // 記錄出庫時的成本
                'balance_before' => $balanceBefore,
                'balance_after' => $inventory->quantity,
                'reason' => $reason ?? '庫存扣減',
                'reference_type' => $referenceType,
                'reference_id' => $referenceId,
                'user_id' => auth()->id(),
                'actual_time' => now(),
            ]);
        });
    }

    public function findInventoryByBatch(int $warehouseId, int $productId, ?string $batchNumber)
    {
        return Inventory::where('warehouse_id', $warehouseId)
            ->where('product_id', $productId)
            ->where('batch_number', $batchNumber)
            ->first();
    }

    public function getDashboardStats(): array
    {
        // 庫存總表 join 安全庫存表，計算低庫存
        $lowStockCount = DB::table('warehouse_product_safety_stocks as ss')
            ->join(DB::raw('(SELECT warehouse_id, product_id, SUM(quantity) as total_qty FROM inventories WHERE deleted_at IS NULL GROUP BY warehouse_id, product_id) as inv'),
                function ($join) {
                    $join->on('ss.warehouse_id', '=', 'inv.warehouse_id')
                         ->on('ss.product_id', '=', 'inv.product_id');
                })
            ->whereRaw('inv.total_qty <= ss.safety_stock')
            ->count();

        return [
            'productsCount' => Product::count(),
            'warehousesCount' => Warehouse::count(),
            'lowStockCount' => $lowStockCount,
            'totalInventoryQuantity' => Inventory::sum('quantity'),
        ];
    }
}