Magento 2: How to add a custom discount and title under discount in cart page

Question

In magento2, how to add a custom discount and title under discount in cart page

I have created a custom promotion in magento2. I needed to do some customization in cart which I am trying to do with salesrule_validator_process event. I needed the rule name and discount values to be modified before applying in cart.

Answer 1

First create file app/code/Company/Module/etc/sales.xml with content

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Sales:etc/sales.xsd">
    <section name="quote">
        <group name="totals">
            <item name="custom_coupon" instance="Company\Module\Model\Quote\Discount" sort_order="500"/>
        </group>
    </section>
</config>

Then create the file app/code/Company/Module/Model/Quote/Discount.php with content

<?php
namespace Company\Module\Model\Quote;

class Discount extends \Magento\Quote\Model\Quote\Address\Total\AbstractTotal
{
    /**
     * @var \Magento\Checkout\Model\Session
     */
    protected $_checkoutSession;  
    /**
     * Discount calculation object
     *
     * @var \Magento\SalesRule\Model\Validator
     */
    protected $calculator;
    /**
     * Core event manager proxy
     *
     * @var \Magento\Framework\Event\ManagerInterface
     */
    protected $eventManager = null;
    /**
     * @var \Magento\Store\Model\StoreManagerInterface
     */
    protected $storeManager;
    /**
     * @var \Magento\Framework\Pricing\PriceCurrencyInterface
     */
    protected $priceCurrency;

    /**
     * @param \Magento\Framework\Event\ManagerInterface $eventManager
     * @param \Magento\Store\Model\StoreManagerInterface $storeManager
     * @param \Magento\SalesRule\Model\Validator $validator
     * @param \Magento\Framework\Pricing\PriceCurrencyInterface $priceCurrency
     */
    public function __construct(
        \Magento\Checkout\Model\Session $checkoutSession,   
        \Magento\Framework\Event\ManagerInterface $eventManager,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Magento\SalesRule\Model\Validator $validator,
        \Magento\Framework\Pricing\PriceCurrencyInterface $priceCurrency
    ) {
        $this->setCode('custom_coupon');
        $this->_checkoutSession = $checkoutSession;  
        $this->eventManager = $eventManager;
        $this->calculator = $validator;
        $this->storeManager = $storeManager;
        $this->priceCurrency = $priceCurrency;
    }
    /**
     * Collect address discount amount
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment
     * @param \Magento\Quote\Model\Quote\Address\Total $total
     * @return $this
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     */
    public function collect(
        \Magento\Quote\Model\Quote $quote,
        \Magento\Quote\Api\Data\ShippingAssignmentInterface $shippingAssignment,
        \Magento\Quote\Model\Quote\Address\Total $total
    ) {
        parent::collect($quote, $shippingAssignment, $total);
        $address             = $shippingAssignment->getShipping()->getAddress();
        $label               = __('Custom Discount');
        $coupon_price = 10;
        $discountAmount      = -$coupon_price;   
        $appliedCartDiscount = 0;
        if($total->getDiscountDescription()) {
            // If a discount exists in cart and another discount is applied, the add both discounts.
            $appliedCartDiscount = $total->getDiscountAmount();
            $discountAmount      = $total->getDiscountAmount()+$discountAmount;
            $label               = $total->getDiscountDescription().', '.$label;
        }    

        $total->setDiscountDescription($label);
        $total->setDiscountAmount($discountAmount);
        $total->setBaseDiscountAmount($discountAmount);
        $total->setSubtotalWithDiscount($total->getSubtotal() + $discountAmount);
        $total->setBaseSubtotalWithDiscount($total->getBaseSubtotal() + $discountAmount);

        if(isset($appliedCartDiscount)) {
            $total->addTotalAmount($this->getCode(), $discountAmount - $appliedCartDiscount);
            $total->addBaseTotalAmount($this->getCode(), $discountAmount - $appliedCartDiscount);
        } else {
            $total->addTotalAmount($this->getCode(), $discountAmount);
            $total->addBaseTotalAmount($this->getCode(), $discountAmount);
        }

        return $this;
    }

    /**
     * Add discount total information to address
     *
     * @param \Magento\Quote\Model\Quote $quote
     * @param \Magento\Quote\Model\Quote\Address\Total $total
     * @return array|null
     */
    public function fetch(\Magento\Quote\Model\Quote $quote, \Magento\Quote\Model\Quote\Address\Total $total)
    {
        $result = null;
        $amount = $total->getDiscountAmount();
        //ONLY return 1 discount. Need to append existing
        //see app/code/Magento/Quote/Model/Quote/Address.php

        if ($amount != 0) { 
            $description = $total->getDiscountDescription();
            $result = [
                'code' => $this->getCode(),
                'title' => strlen($description) ? __('Discount (%1)', $description) : __('Discount'),
                'value' => $amount
            ];
        }
        return $result;
    }
}