Validation on the Update Cart button on Cart page

cmnq_min_max_quantity.php

<? php
/*
* Get the total quantity of the product available in the cart.
*/ 
function wc_qty_get_cart_qty( $product_id , $cart_item_key = '' ) {
	global $woocommerce;
	$running_qty = 0; // iniializing quantity to 0

	// search the cart for the product in and calculate quantity.
	foreach($woocommerce->cart->get_cart() as $other_cart_item_keys => $values ) {
		if ( $product_id == $values['product_id'] ) {

			if ( $cart_item_key == $other_cart_item_keys ) {
				continue;
			}

			$running_qty += (int) $values['quantity'];
		}
	}

	return $running_qty;
}

/*
* Validate product quantity when cart is UPDATED
*/

function wc_qty_update_cart_validation( $passed, $cart_item_key, $values, $quantity ) {
	$product_min = wc_get_product_min_limit( $values['product_id'] );
	$product_max = wc_get_product_max_limit( $values['product_id'] );

	if ( ! empty( $product_min ) ) {
		// min is empty
		if ( false !== $product_min ) {
			$new_min = $product_min;
		} else {
			// neither max is set, so get out
			return $passed;
		}
	}

	if ( ! empty( $product_max ) ) {
		// min is empty
		if ( false !== $product_max ) {
			$new_max = $product_max;
		} else {
			// neither max is set, so get out
			return $passed;
		}
	}

	$product = wc_get_product( $values['product_id'] );
	$already_in_cart = wc_qty_get_cart_qty( $values['product_id'], $cart_item_key );

	if ( isset( $new_max) && ( $already_in_cart + $quantity ) > $new_max ) {
		wc_add_notice( apply_filters( 'wc_qty_error_message', sprintf( __( 'You can add a maximum of %1$s %2$s\'s to %3$s.', 'woocommerce-max-quantity' ),
					$new_max,
					$product->get_name(),
					'<a href="' . esc_url( wc_get_cart_url() ) . '">' . __( 'your cart', 'woocommerce-max-quantity' ) . '</a>'),
				$new_max ),
		'error' );
		$passed = false;
	}

	if ( isset( $new_min) && ( $already_in_cart + $quantity )  < $new_min ) {
		wc_add_notice( apply_filters( 'wc_qty_error_message', sprintf( __( 'You should have minimum of %1$s %2$s\'s to %3$s.', 'woocommerce-max-quantity' ),
					$new_min,
					$product->get_name(),
					'<a href="' . esc_url( wc_get_cart_url() ) . '">' . __( 'your cart', 'woocommerce-max-quantity' ) . '</a>'),
				$new_min ),
		'error' );
		$passed = false;
	}

	return $passed;
}
add_filter( 'woocommerce_update_cart_validation', 'wc_qty_update_cart_validation', 1, 4 );

?>