vaishnavi-ecommerce-backend/src/services/inventoryService.js

// services/inventoryService.js - COMPLETE INVENTORY SYSTEM
const { prisma } = require('../config/database');
const Product = require('../models/mongodb/Product');

/**
 * ✅ Auto-reduce stock when order is DELIVERED
 */
async function reduceStockOnDelivery(orderId) {
  try {
    const order = await prisma.order.findUnique({
      where: { id: orderId },
      include: { items: true },
    });

    if (!order || order.status !== 'DELIVERED') return null;

    const results = [];

    for (const item of order.items) {
      const product = await Product.findById(item.productId);
      if (!product) continue;

      let previousStock, newStock;

      if (product.hasVariants && product.variants?.length > 0) {
        // ✅ Reduce from matching variant by SKU
        previousStock = product.variants
          .filter(v => v.isActive)
          .reduce((sum, v) => sum + (v.inventory?.quantity || 0), 0);

        const variantIndex = product.variants.findIndex(
          v => v.sku === item.productSku
        );

        if (variantIndex !== -1) {
          const currentQty =
            product.variants[variantIndex].inventory?.quantity || 0;
          product.variants[variantIndex].inventory.quantity = Math.max(
            0,
            currentQty - item.quantity
          );
          await product.save();
        }

        newStock = product.variants
          .filter(v => v.isActive)
          .reduce((sum, v) => sum + (v.inventory?.quantity || 0), 0);
      } else {
        // ✅ Non-variant product
        previousStock = product.stock || 0;
        newStock = Math.max(0, previousStock - item.quantity);
        await Product.findByIdAndUpdate(item.productId, {
          stock: newStock,
          updatedAt: new Date(),
        });
      }

      await prisma.inventoryLog.create({
        data: {
          productId: item.productId,
          productName: item.productName || product.name,
          type: 'SOLD',
          quantityChange: -item.quantity,
          previousStock,
          newStock,
          orderId,
          notes: `Order ${order.orderNumber} delivered`,
        },
      });

      results.push({
        productId: item.productId,
        productName: product.name,
        reduced: item.quantity,
        previousStock,
        newStock,
      });
    }

    return results;
  } catch (error) {
    console.error('❌ Stock reduction error:', error);
    throw error;
  }
}

/**
 * ✅ Get low stock products
 */
async function getLowStockProducts(threshold = 10) {
  try {
    const products = await Product.find({ status: 'active' }).lean();

    const withStock = products.map(product => {
      let totalStock = 0;

      if (product.hasVariants && product.variants?.length > 0) {
        totalStock = product.variants
          .filter(v => v.isActive)
          .reduce((sum, v) => sum + (v.inventory?.quantity || 0), 0);
      } else {
        totalStock = product.stock || 0;
      }

      return {
        _id: product._id.toString(),
        name: product.name,
        slug: product.slug,
        stock: totalStock,
        basePrice: product.basePrice,
        hasVariants: product.hasVariants,
        status:
          totalStock === 0
            ? 'OUT_OF_STOCK'
            : totalStock <= 5
              ? 'CRITICAL'
              : 'LOW',
        displayImage: getProductImage(product),
      };
    });

    return withStock
      .filter(p => p.stock <= threshold)
      .sort((a, b) => a.stock - b.stock)
      .slice(0, threshold);
  } catch (error) {
    console.error('Error fetching low stock:', error);
    return [];
  }
}

/**
 * ✅ Get inventory stats for dashboard
 */
async function getInventoryStats() {
  try {
    const products = await Product.find({ status: 'active' }).lean();

    let outOfStock = 0,
      criticalStock = 0,
      lowStock = 0,
      inStock = 0;

    products.forEach(product => {
      let stock = 0;

      if (product.hasVariants && product.variants?.length > 0) {
        stock = product.variants
          .filter(v => v.isActive)
          .reduce((sum, v) => sum + (v.inventory?.quantity || 0), 0);
      } else {
        stock = product.stock || 0;
      }

      if (stock === 0) outOfStock++;
      else if (stock <= 5) criticalStock++;
      else if (stock <= 10) lowStock++;
      else inStock++;
    });

    return {
      totalProducts: products.length,
      outOfStock,
      criticalStock,
      lowStock,
      inStock,
    };
  } catch (error) {
    console.error('Error fetching inventory stats:', error);
    return null;
  }
}

/**
 * ✅ Manual stock adjustment (Admin)
 */
async function adjustStock(
  productId,
  variantSku = null,
  quantity,
  type,
  notes,
  adminId
) {
  try {
    const product = await Product.findById(productId);
    if (!product) throw new Error('Product not found');

    let previousStock, newStock;

    if (product.hasVariants && product.variants?.length > 0 && variantSku) {
      // ✅ Adjust specific variant
      const variantIndex = product.variants.findIndex(
        v => v.sku === variantSku
      );
      if (variantIndex === -1) throw new Error('Variant not found');

      const currentQty =
        product.variants[variantIndex].inventory?.quantity || 0;
      previousStock = currentQty;

      if (type === 'ADD') newStock = currentQty + quantity;
      else if (type === 'REMOVE') newStock = Math.max(0, currentQty - quantity);
      else if (type === 'SET') newStock = quantity;
      else throw new Error('Invalid type');

      product.variants[variantIndex].inventory.quantity = newStock;
      await product.save();
    } else {
      // ✅ Non-variant product
      previousStock = product.stock || 0;

      if (type === 'ADD') newStock = previousStock + quantity;
      else if (type === 'REMOVE')
        newStock = Math.max(0, previousStock - quantity);
      else if (type === 'SET') newStock = quantity;
      else throw new Error('Invalid type');

      await Product.findByIdAndUpdate(productId, {
        stock: newStock,
        updatedAt: new Date(),
      });
    }

    await prisma.inventoryLog.create({
      data: {
        productId,
        productName: product.name,
        type: type === 'ADD' ? 'RESTOCK' : 'ADJUSTMENT',
        quantityChange: type === 'ADD' ? quantity : -quantity,
        previousStock,
        newStock,
        notes: notes || `Manual ${type} by admin`,
        adjustedBy: adminId,
      },
    });

    return {
      success: true,
      productName: product.name,
      previousStock,
      newStock,
    };
  } catch (error) {
    console.error('Error adjusting stock:', error);
    throw error;
  }
}

function getProductImage(product) {
  return (
    product.images?.gallery?.[0] ||
    product.images?.primary ||
    product.variants?.[0]?.images?.[0] ||
    'https://via.placeholder.com/300'
  );
}

module.exports = {
  reduceStockOnDelivery,
  getLowStockProducts,
  getInventoryStats,
  adjustStock,
};