<form method="POST">
    <h3>Editing: class-wc-email-customer-invoice.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
/**
 * Class WC_Email_Customer_Invoice file.
 *
 * @package WooCommerce\Emails
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

if ( ! class_exists( 'WC_Email_Customer_Invoice', false ) ) :

	/**
	 * Order details email.
	 *
	 * An email sent to the customer via admin, that summarizes the details of their order. This was
	 * historically referred to as the 'invoice', and for backwards compatibility reasons that is still
	 * reflected in the class name (although on a user-level we have moved away from that nomenclature).
	 *
	 * @class       WC_Email_Customer_Invoice
	 * @version     3.5.0
	 * @package     WooCommerce\Classes\Emails
	 * @extends     WC_Email
	 */
	class WC_Email_Customer_Invoice extends WC_Email {

		/**
		 * Constructor.
		 */
		public function __construct() {
			$this-&gt;id             = 'customer_invoice';
			$this-&gt;customer_email = true;
			$this-&gt;title          = __( 'Order details', 'woocommerce' );
			$this-&gt;description    = __( 'Order detail emails can be sent to customers containing their order information and payment links.', 'woocommerce' );
			$this-&gt;template_html  = 'emails/customer-invoice.php';
			$this-&gt;template_plain = 'emails/plain/customer-invoice.php';
			$this-&gt;placeholders   = array(
				'{order_date}'   =&gt; '',
				'{order_number}' =&gt; '',
			);

			// Call parent constructor.
			parent::__construct();

			$this-&gt;manual = true;
		}

		/**
		 * Get email subject.
		 *
		 * @param bool $paid Whether the order has been paid or not.
		 * @since  3.1.0
		 * @return string
		 */
		public function get_default_subject( $paid = false ) {
			return __( 'Details for order #{order_number} on {site_title}', 'woocommerce' );
		}

		/**
		 * Get email heading.
		 *
		 * @param bool $paid Whether the order has been paid or not.
		 * @since  3.1.0
		 * @return string
		 */
		public function get_default_heading( $paid = false ) {
			return __( 'Details for order #{order_number}', 'woocommerce' );
		}

		/**
		 * Get email subject.
		 *
		 * @return string
		 */
		public function get_subject() {
			if ( $this-&gt;object-&gt;has_status( array( 'completed', 'processing' ) ) ) {
				$subject = $this-&gt;get_option( 'subject_paid', $this-&gt;get_default_subject( true ) );

				return apply_filters( 'woocommerce_email_subject_customer_invoice_paid', $this-&gt;format_string( $subject ), $this-&gt;object, $this );
			}

			$subject = $this-&gt;get_option( 'subject', $this-&gt;get_default_subject() );
			return apply_filters( 'woocommerce_email_subject_customer_invoice', $this-&gt;format_string( $subject ), $this-&gt;object, $this );
		}

		/**
		 * Get email heading.
		 *
		 * @return string
		 */
		public function get_heading() {
			if ( $this-&gt;object-&gt;has_status( wc_get_is_paid_statuses() ) ) {
				$heading = $this-&gt;get_option( 'heading_paid', $this-&gt;get_default_heading( true ) );
				return apply_filters( 'woocommerce_email_heading_customer_invoice_paid', $this-&gt;format_string( $heading ), $this-&gt;object, $this );
			}

			$heading = $this-&gt;get_option( 'heading', $this-&gt;get_default_heading() );
			return apply_filters( 'woocommerce_email_heading_customer_invoice', $this-&gt;format_string( $heading ), $this-&gt;object, $this );
		}

		/**
		 * Default content to show below main email content.
		 *
		 * @since 3.7.0
		 * @return string
		 */
		public function get_default_additional_content() {
			return __( 'Thanks for using {site_url}!', 'woocommerce' );
		}

		/**
		 * Trigger the sending of this email.
		 *
		 * @param int      $order_id The order ID.
		 * @param WC_Order $order Order object.
		 */
		public function trigger( $order_id, $order = false ) {
			$this-&gt;setup_locale();

			if ( $order_id &amp;&amp; ! is_a( $order, 'WC_Order' ) ) {
				$order = wc_get_order( $order_id );
			}

			if ( is_a( $order, 'WC_Order' ) ) {
				$this-&gt;object                         = $order;
				$this-&gt;recipient                      = $this-&gt;object-&gt;get_billing_email();
				$this-&gt;placeholders['{order_date}']   = wc_format_datetime( $this-&gt;object-&gt;get_date_created() );
				$this-&gt;placeholders['{order_number}'] = $this-&gt;object-&gt;get_order_number();
			}

			if ( $this-&gt;get_recipient() ) {
				$this-&gt;send( $this-&gt;get_recipient(), $this-&gt;get_subject(), $this-&gt;get_content(), $this-&gt;get_headers(), $this-&gt;get_attachments() );
			}

			$this-&gt;restore_locale();
		}

		/**
		 * Get content html.
		 *
		 * @return string
		 */
		public function get_content_html() {
			return wc_get_template_html(
				$this-&gt;template_html,
				array(
					'order'              =&gt; $this-&gt;object,
					'email_heading'      =&gt; $this-&gt;get_heading(),
					'additional_content' =&gt; $this-&gt;get_additional_content(),
					'sent_to_admin'      =&gt; false,
					'plain_text'         =&gt; false,
					'email'              =&gt; $this,
				)
			);
		}

		/**
		 * Get content plain.
		 *
		 * @return string
		 */
		public function get_content_plain() {
			return wc_get_template_html(
				$this-&gt;template_plain,
				array(
					'order'              =&gt; $this-&gt;object,
					'email_heading'      =&gt; $this-&gt;get_heading(),
					'additional_content' =&gt; $this-&gt;get_additional_content(),
					'sent_to_admin'      =&gt; false,
					'plain_text'         =&gt; true,
					'email'              =&gt; $this,
				)
			);
		}

		/**
		 * Initialise settings form fields.
		 */
		public function init_form_fields() {
			/* translators: %s: list of placeholders */
			$placeholder_text  = sprintf( __( 'Available placeholders: %s', 'woocommerce' ), '&lt;code&gt;' . esc_html( implode( '&lt;/code&gt;, &lt;code&gt;', array_keys( $this-&gt;placeholders ) ) ) . '&lt;/code&gt;' );
			$this-&gt;form_fields = array(
				'subject'            =&gt; array(
					'title'       =&gt; __( 'Subject', 'woocommerce' ),
					'type'        =&gt; 'text',
					'desc_tip'    =&gt; true,
					'description' =&gt; $placeholder_text,
					'placeholder' =&gt; $this-&gt;get_default_subject(),
					'default'     =&gt; '',
				),
				'heading'            =&gt; array(
					'title'       =&gt; __( 'Email heading', 'woocommerce' ),
					'type'        =&gt; 'text',
					'desc_tip'    =&gt; true,
					'description' =&gt; $placeholder_text,
					'placeholder' =&gt; $this-&gt;get_default_heading(),
					'default'     =&gt; '',
				),
				'subject_paid'       =&gt; array(
					'title'       =&gt; __( 'Subject (paid)', 'woocommerce' ),
					'type'        =&gt; 'text',
					'desc_tip'    =&gt; true,
					'description' =&gt; $placeholder_text,
					'placeholder' =&gt; $this-&gt;get_default_subject( true ),
					'default'     =&gt; '',
				),
				'heading_paid'       =&gt; array(
					'title'       =&gt; __( 'Email heading (paid)', 'woocommerce' ),
					'type'        =&gt; 'text',
					'desc_tip'    =&gt; true,
					'description' =&gt; $placeholder_text,
					'placeholder' =&gt; $this-&gt;get_default_heading( true ),
					'default'     =&gt; '',
				),
				'additional_content' =&gt; array(
					'title'       =&gt; __( 'Additional content', 'woocommerce' ),
					'description' =&gt; __( 'Text to appear below the main email content.', 'woocommerce' ) . ' ' . $placeholder_text,
					'css'         =&gt; 'width:400px; height: 75px;',
					'placeholder' =&gt; __( 'N/A', 'woocommerce' ),
					'type'        =&gt; 'textarea',
					'default'     =&gt; $this-&gt;get_default_additional_content(),
					'desc_tip'    =&gt; true,
				),
				'email_type'         =&gt; array(
					'title'       =&gt; __( 'Email type', 'woocommerce' ),
					'type'        =&gt; 'select',
					'description' =&gt; __( 'Choose which format of email to send.', 'woocommerce' ),
					'default'     =&gt; 'html',
					'class'       =&gt; 'email_type wc-enhanced-select',
					'options'     =&gt; $this-&gt;get_email_type_options(),
					'desc_tip'    =&gt; true,
				),
			);
		}
	}

endif;

return new WC_Email_Customer_Invoice();
</textarea><br>
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