const Cart = require('../models/Cart');
const Product = require('../models/Product');
const Coupon = require('../models/Coupon');
const { successResponse, errorResponse } = require('../utils/apiResponse');

const getCart = async (req, res, next) => {
  try {
    const userId = req.user ? req.user._id : null;
    const sessionId = req.headers['x-session-id'] || null;

    let cart = null;
    if (userId) {
      cart = await Cart.findOne({ user: userId }).populate('items.product');
    } else if (sessionId) {
      cart = await Cart.findOne({ sessionId }).populate('items.product');
    }

    if (!cart) {
      cart = { items: [], couponCode: '', discountAmount: 0 };
    }

    return successResponse(res, 'Cart retrieved', cart);
  } catch (error) {
    next(error);
  }
};

const addToCart = async (req, res, next) => {
  try {
    const { productId, quantity = 1, variantColor = '', variantFinish = '' } = req.body;
    const userId = req.user ? req.user._id : null;
    const sessionId = req.headers['x-session-id'] || 'guest-' + Date.now();

    const product = await Product.findById(productId);
    if (!product) {
      return errorResponse(res, 'Product not found', [], 404);
    }

    // Inventory check
    if (product.stock < quantity) {
      return errorResponse(res, `Only ${product.stock} items remaining in stock`, [], 400);
    }

    let cart;
    if (userId) {
      cart = await Cart.findOne({ user: userId });
    } else {
      cart = await Cart.findOne({ sessionId });
    }

    const price = product.salePrice > 0 ? product.salePrice : product.price;

    if (!cart) {
      cart = new Cart({
        user: userId,
        sessionId,
        items: [{ product: productId, quantity, variantColor, variantFinish, price }]
      });
    } else {
      const existingItemIndex = cart.items.findIndex(
        item => item.product.toString() === productId && item.variantColor === variantColor
      );

      if (existingItemIndex > -1) {
        cart.items[existingItemIndex].quantity += Number(quantity);
      } else {
        cart.items.push({ product: productId, quantity, variantColor, variantFinish, price });
      }
    }

    await cart.save();
    const updatedCart = await Cart.findById(cart._id).populate('items.product');
    return successResponse(res, 'Product added to cart', updatedCart);
  } catch (error) {
    next(error);
  }
};

const updateCartItem = async (req, res, next) => {
  try {
    const { itemId, quantity } = req.body;
    const userId = req.user ? req.user._id : null;
    const sessionId = req.headers['x-session-id'];

    const cart = userId 
      ? await Cart.findOne({ user: userId })
      : await Cart.findOne({ sessionId });

    if (!cart) return errorResponse(res, 'Cart not found', [], 404);

    const item = cart.items.id(itemId);
    if (!item) return errorResponse(res, 'Item not found in cart', [], 404);

    if (quantity <= 0) {
      cart.items.pull(itemId);
    } else {
      item.quantity = quantity;
    }

    await cart.save();
    const updatedCart = await Cart.findById(cart._id).populate('items.product');
    return successResponse(res, 'Cart updated', updatedCart);
  } catch (error) {
    next(error);
  }
};

const removeCartItem = async (req, res, next) => {
  try {
    const userId = req.user ? req.user._id : null;
    const sessionId = req.headers['x-session-id'];

    const cart = userId 
      ? await Cart.findOne({ user: userId })
      : await Cart.findOne({ sessionId });

    if (cart) {
      cart.items = cart.items.filter(item => item._id.toString() !== req.params.itemId);
      await cart.save();
    }

    const updatedCart = cart ? await Cart.findById(cart._id).populate('items.product') : { items: [] };
    return successResponse(res, 'Item removed from cart', updatedCart);
  } catch (error) {
    next(error);
  }
};

const applyCoupon = async (req, res, next) => {
  try {
    const { code } = req.body;
    const coupon = await Coupon.findOne({ code: code.toUpperCase(), isActive: true });

    if (!coupon || coupon.endDate < new Date()) {
      return errorResponse(res, 'Invalid or expired coupon code', [], 400);
    }

    return successResponse(res, 'Coupon applied successfully', {
      code: coupon.code,
      discountType: coupon.discountType,
      discountValue: coupon.discountValue,
      minPurchaseAmount: coupon.minPurchaseAmount
    });
  } catch (error) {
    next(error);
  }
};

module.exports = { getCart, addToCart, updateCartItem, removeCartItem, applyCoupon };