WooCommerce - Pay Button sample

woocommerce-pay-button-sample.php

<?php
/**
 * Plugin Name: Test "pay button" support
 */

add_action( 'plugins_loaded', function() {
    class My_Custom_Gateway extends WC_Payment_Gateway {
        public function __construct() {
            $this->id                 = 'custom_gateway';
            $this->has_fields         = false;
            $this->method_title       = 'Custom Gateway';
            $this->method_description = 'Custom Gateway for tests';
            $this->pay_button_id      = 'custom-pay-button'; // Pay button ID.
            $this->supports           = array(
                'products',
                'pay_button', // Pay button supporte declared.
            );

            // Load the settings.
            $this->init_form_fields();
            $this->init_settings();
        }

        /**
         * Initialise Gateway Settings Form Fields.
         */
        public function init_form_fields() {
            $this->form_fields = array(
                'enabled' => array(
                    'title'   => 'Enable/Disable',
                    'type'    => 'checkbox',
                    'label'   => '',
                    'default' => 'yes',
                ),
            );
        }
    }

    // Register class.
    add_filter(
        'woocommerce_payment_gateways',
        function( $gateways ) {
            $gateways[] = 'My_Custom_Gateway';

            return $gateways;
        }
    );

    /**
     * Sample button implementation.
     */
    add_action( 'wp_footer', function() {
        echo '<script>jQuery( "#custom-pay-button" ).text( "Pay now" ).css( "color", "#fff" ).css( "background", "#222" ).css( "padding", "5px" ).css( "max-width", "150px" );</script>';
    } );
}, 10 );