Contact Form: Send all emails through wrapper to ensure consistency

Previously the two `wp_mail()` calls in `Grunion_Contact_Form::process_submission()` had extra filters around them in order to support HTML messages. The `wp_mail()` call in `grunion_ajax_spam()` was missing those filters, though. That resulted in ham messages being sent with a `plain-text` content type, but with HTML markup in the body.

Sending all `wp_mail()` calls fixes that particular issue, and also makes it much less likely that a similar bug will happen in the future, because it is DRY.

Fixes #7179

modules/contact-form/admin.php

@@ -696,7 +696,7 @@ function grunion_ajax_spam() {
 			 */
 			$subject = apply_filters( 'contact_form_subject', $content_fields['_feedback_subject'], $content_fields['_feedback_all_fields'] );
 
-			wp_mail( $to, $subject, $message, $headers );
+			Grunion_Contact_Form::wp_mail( $to, $subject, $message, $headers );
 		}
 	} elseif( $_POST['make_it'] == 'publish' ) {
 		if ( ! current_user_can($post_type_object->cap->delete_post, $post_id) ) {

modules/contact-form/grunion-contact-form.php

@@ -2150,8 +2150,6 @@ function process_submission() {
 			wp_schedule_event( time() + 250, 'daily', 'grunion_scheduled_delete' );
 		}
 
-		add_filter( 'wp_mail_content_type', __CLASS__ . '::get_mail_content_type' );
-		add_action( 'phpmailer_init', __CLASS__ . '::add_plain_text_alternative' );
 		if (
 			$is_spam !== true &&
 			/**
@@ -2166,7 +2164,7 @@ function process_submission() {
 			 */
 			true === apply_filters( 'grunion_should_send_email', true, $post_id )
 		) {
-			wp_mail( $to, "{$spam}{$subject}", $message, $headers );
+			self::wp_mail( $to, "{$spam}{$subject}", $message, $headers );
 		} elseif (
 			true === $is_spam &&
 			/**
@@ -2180,10 +2178,8 @@ function process_submission() {
 			 */
 			apply_filters( 'grunion_still_email_spam', false ) == true
 		) { // don't send spam by default.  Filterable.
-			wp_mail( $to, "{$spam}{$subject}", $message, $headers );
+			self::wp_mail( $to, "{$spam}{$subject}", $message, $headers );
 		}
-		remove_filter( 'wp_mail_content_type', __CLASS__ . '::get_mail_content_type' );
-		remove_action( 'phpmailer_init', __CLASS__ . '::add_plain_text_alternative' );
 
 		if ( defined( 'DOING_AJAX' ) && DOING_AJAX ) {
 			return self::success_message( $post_id, $this );
@@ -2217,6 +2213,29 @@ function process_submission() {
 		exit;
 	}
 
+	/**
+	 * Wrapper for wp_mail() that enables HTML messages with text alternatives
+	 *
+	 * @param string|array $to          Array or comma-separated list of email addresses to send message.
+	 * @param string       $subject     Email subject.
+	 * @param string       $message     Message contents.
+	 * @param string|array $headers     Optional. Additional headers.
+	 * @param string|array $attachments Optional. Files to attach.
+	 *
+	 * @return bool Whether the email contents were sent successfully.
+	 */
+	public static function wp_mail( $to, $subject, $message, $headers = '', $attachments = array() ) {
+		add_filter( 'wp_mail_content_type', __CLASS__ . '::get_mail_content_type' );
+		add_action( 'phpmailer_init',       __CLASS__ . '::add_plain_text_alternative' );
+
+		$result = wp_mail( $to, $subject, $message, $headers, $attachments );
+
+		remove_filter( 'wp_mail_content_type', __CLASS__ . '::get_mail_content_type' );
+		remove_action( 'phpmailer_init',       __CLASS__ . '::add_plain_text_alternative' );
+
+		return $result;
+	}
+
 	/**
 	 * Add a display name part to an email address
 	 *