eCommerce-backend/src/controllers/products/recommendation.js

// controllers/products/recommendationController.js

const Product = require('../../models/mongodb/Product');
const { prisma } = require('../../config/database');

/**
 * @desc    Get recommendations for a product
 * @route   GET /api/products/:slug/recommendations
 * @access  Public
 */
const getProductRecommendations = async (req, res, next) => {
  try {
    const { slug } = req.params;
    const { limit = 12 } = req.query;

    // Get the current product
    const currentProduct = await Product.findOne({ slug, status: 'active' });

    if (!currentProduct) {
      return res.status(404).json({
        success: false,
        message: 'Product not found',
      });
    }

    // Build recommendation query
    const recommendations = await getRecommendedProducts(
      currentProduct,
      parseInt(limit)
    );

    res.status(200).json({
      success: true,
      count: recommendations.length,
      data: recommendations,
    });
  } catch (error) {
    console.error('Get recommendations error:', error);
    next(error);
  }
};

/**
 * @desc    Get "Customers also bought" products
 * @route   GET /api/products/:slug/also-bought
 * @access  Public
 */
const getAlsoBoughtProducts = async (req, res, next) => {
  try {
    const { slug } = req.params;
    const { limit = 8 } = req.query;

    const currentProduct = await Product.findOne({ slug, status: 'active' });

    if (!currentProduct) {
      return res.status(404).json({
        success: false,
        message: 'Product not found',
      });
    }

    // Get products frequently bought together
    const alsoBought = await getFrequentlyBoughtTogether(
      currentProduct._id.toString(),
      parseInt(limit)
    );

    res.status(200).json({
      success: true,
      count: alsoBought.length,
      data: alsoBought,
    });
  } catch (error) {
    console.error('Get also bought error:', error);
    next(error);
  }
};

/**
 * @desc    Get similar products
 * @route   GET /api/products/:slug/similar
 * @access  Public
 */
const getSimilarProducts = async (req, res, next) => {
  try {
    const { slug } = req.params;
    const { limit = 10 } = req.query;

    const currentProduct = await Product.findOne({ slug, status: 'active' });

    if (!currentProduct) {
      return res.status(404).json({
        success: false,
        message: 'Product not found',
      });
    }

    // Get similar products based on attributes
    const similar = await getSimilarProductsByAttributes(
      currentProduct,
      parseInt(limit)
    );

    res.status(200).json({
      success: true,
      count: similar.length,
      data: similar,
    });
  } catch (error) {
    console.error('Get similar products error:', error);
    next(error);
  }
};

/**
 * @desc    Get personalized recommendations for user
 * @route   GET /api/products/recommendations/personalized
 * @access  Private
 */
const getPersonalizedRecommendations = async (req, res, next) => {
  try {
    const userId = req.user?.id;
    const { limit = 20 } = req.query;

    if (!userId) {
      // Return popular products for non-authenticated users
      const popularProducts = await Product.find({ status: 'active' })
        .sort({ purchaseCount: -1, viewCount: -1 })
        .limit(parseInt(limit));

      return res.status(200).json({
        success: true,
        count: popularProducts.length,
        data: popularProducts,
      });
    }

    // Get user's purchase history
    const userOrders = await prisma.order.findMany({
      where: {
        userId,
        status: 'DELIVERED',
      },
      include: {
        items: true,
      },
      take: 10,
      orderBy: { createdAt: 'desc' },
    });

    // Get user's wishlist
    const wishlist = await prisma.wishlistItem.findMany({
      where: { userId },
      take: 20,
    });

    // Extract product IDs
    const purchasedProductIds = userOrders.flatMap((order) =>
      order.items.map((item) => item.productId)
    );
    const wishlistProductIds = wishlist.map((item) => item.productId);

    // Get categories and tags from purchased products
    const purchasedProducts = await Product.find({
      _id: { $in: purchasedProductIds },
    });

    const categories = [...new Set(purchasedProducts.map((p) => p.category))];
    const tags = [
      ...new Set(purchasedProducts.flatMap((p) => p.tags || [])),
    ];

    // Build personalized recommendations
    const recommendations = await Product.find({
      status: 'active',
      _id: {
        $nin: [...purchasedProductIds, ...wishlistProductIds],
      },
      $or: [
        { category: { $in: categories } },
        { tags: { $in: tags } },
        { isFeatured: true },
      ],
    })
      .sort({ purchaseCount: -1, viewCount: -1 })
      .limit(parseInt(limit));

    res.status(200).json({
      success: true,
      count: recommendations.length,
      data: recommendations,
    });
  } catch (error) {
    console.error('Get personalized recommendations error:', error);
    next(error);
  }
};

/**
 * Helper Functions
 */

// Get recommended products based on multiple factors
async function getRecommendedProducts(currentProduct, limit) {
  const priceRange = {
    min: currentProduct.basePrice * 0.7,
    max: currentProduct.basePrice * 1.3,
  };

  // Score-based recommendation
  const recommendations = await Product.aggregate([
    {
      $match: {
        _id: { $ne: currentProduct._id },
        status: 'active',
      },
    },
    {
      $addFields: {
        score: {
          $add: [
            { $cond: [{ $eq: ['$category', currentProduct.category] }, 50, 0] },
            {
              $cond: [
                {
                  $and: [
                    { $gte: ['$basePrice', priceRange.min] },
                    { $lte: ['$basePrice', priceRange.max] },
                  ],
                },
                30,
                0,
              ],
            },
            {
              $multiply: [
                {
                  $size: {
                    $ifNull: [
                      {
                        $setIntersection: [
                          { $ifNull: ['$tags', []] },
                          currentProduct.tags || [],
                        ],
                      },
                      [],
                    ],
                  },
                },
                5,
              ],
            },
            { $cond: ['$isFeatured', 20, 0] },
            { $divide: [{ $ifNull: ['$viewCount', 0] }, 100] },
            { $divide: [{ $multiply: [{ $ifNull: ['$purchaseCount', 0] }, 10] }, 10] },
          ],
        },
      },
    },
    { $sort: { score: -1 } },
    { $limit: limit },
  ]);

  return recommendations;
}

// Get frequently bought together products
async function getFrequentlyBoughtTogether(productId, limit) {
  try {
    const ordersWithProduct = await prisma.orderItem.findMany({
      where: { productId },
      select: { orderId: true },
      distinct: ['orderId'],
    });

    if (ordersWithProduct.length === 0) {
      const product = await Product.findById(productId);
      return await Product.find({
        _id: { $ne: productId },
        category: product.category,
        status: 'active',
      })
        .sort({ purchaseCount: -1 })
        .limit(limit);
    }

    const orderIds = ordersWithProduct.map((item) => item.orderId);

    const otherProducts = await prisma.orderItem.findMany({
      where: {
        orderId: { in: orderIds },
        productId: { not: productId },
      },
      select: { productId: true },
    });

    const productFrequency = {};
    otherProducts.forEach((item) => {
      productFrequency[item.productId] =
        (productFrequency[item.productId] || 0) + 1;
    });

    const sortedProductIds = Object.entries(productFrequency)
      .sort(([, a], [, b]) => b - a)
      .slice(0, limit)
      .map(([id]) => id);

    const products = await Product.find({
      _id: { $in: sortedProductIds },
      status: 'active',
    });

    return products;
  } catch (error) {
    console.error('Get frequently bought together error:', error);
    return [];
  }
}

// Get similar products by attributes
async function getSimilarProductsByAttributes(currentProduct, limit) {
  const similar = await Product.find({
    _id: { $ne: currentProduct._id },
    status: 'active',
    $or: [
      { category: currentProduct.category },
      { tags: { $in: currentProduct.tags || [] } },
      { brand: currentProduct.brand },
    ],
  })
    .sort({
      purchaseCount: -1,
      viewCount: -1,
    })
    .limit(limit);

  return similar;
}

module.exports = {
  getProductRecommendations,
  getAlsoBoughtProducts,
  getSimilarProducts,
  getPersonalizedRecommendations,
};