Mage2\Cart\Controllers\CartController::addToCart PHP Method

    public function addToCart(Request $request, $id)
    {
        $cart = Session::get('cart');
        $product = Product::findorfail($id);
        if (null !== $request->get('qty') && !isset($cart[$id])) {
            $cart[$id] = ['id' => $id, 'qty' => $request->get('qty'), 'price' => $product->price, 'tax_amount' => $product->getTaxAmount(), 'model' => $product];
        } elseif (null !== $request->get('qty') && isset($cart[$id])) {
            $cart[$id]['qty'] += $request->get('qty');
        } elseif (null === $request->get('qty') && isset($cart[$id])) {
            $cart[$id]['qty'] += 1;
        } else {
            $cart[$id] = ['id' => $id, 'qty' => 1, 'price' => $product->price, 'tax_amount' => $product->getTaxAmount(), 'model' => $product];
        }
        Session::put('cart', $cart);
        return redirect()->back()->with('notificationText', 'Product Added to Cart Successfully!');
    }