Add support for email success and failure logs

composer.json

@@ -7,7 +7,9 @@
   "require": {
     "php": "^7.3|^8.0",
     "symfony/yaml": "^5.1",
-    "studiometa/webpack-config": "^4.0"
+    "studiometa/webpack-config": "^4.0",
+    "monolog/monolog": "^2.9|^3.0",
+    "psr/log": "^1.1"
   },
   "require-dev": {
     "squizlabs/php_codesniffer": "^3.4",

src/Managers/EmailManager.php

@@ -7,17 +7,47 @@
 
 namespace Studiometa\WPToolkit\Managers;
 
+use WP_Error;
+use Monolog\Logger;
+use Monolog\Handler\StreamHandler;
+use Psr\Log\LoggerInterface;
 use PHPMailer\PHPMailer\PHPMailer;
 use function Studiometa\WPToolkit\env;
 
 /** Class **/
 class EmailManager implements ManagerInterface {
+	/**
+	 * Logger instance.
+	 *
+	 * @var LoggerInterface|null;
+	 */
+	private $logger;
+
+	/**
+	 * Class constructor.
+	 *
+	 * @param LoggerInterface|null $logger A logger instance to log mail actions.
+	 */
+	public function __construct( ?LoggerInterface $logger = null ) {
+		if ( ! is_null( $logger ) ) {
+			$this->logger = $logger;
+		} elseif ( env( 'MAIL_LOG' ) ) {
+			$this->logger = new Logger( 'email' );
+			$this->logger->pushHandler( new StreamHandler( env( 'MAIL_LOG' ) ) );
+		}
+	}
+
 	/**
 	 * {@inheritdoc}
 	 */
 	public function run() {
 		if ( 'smtp' === env( 'MAIL_MAILER' ) ) {
-			add_action( 'phpmailer_init', array( $this, 'configure_smtp' ), 10, 1 );
+			add_action( 'phpmailer_init', array( $this, 'configure_smtp' ) );
+		}
+
+		if ( $this->logger ) {
+			add_action( 'wp_mail_succeeded', array( $this, 'log_success' ) );
+			add_action( 'wp_mail_failed', array( $this, 'log_failure' ) );
 		}
 	}
 
@@ -38,4 +68,36 @@ public function configure_smtp( PHPMailer $mailer ): void {
 		$mailer->IsSMTP();
 		// phpcs:enable WordPress.NamingConventions.ValidVariableName.UsedPropertyNotSnakeCase
 	}
+
+	/**
+	 * Log successfully sent mails.
+	 *
+	 * @param array{to: string[], subject: string, message: string, headers: string[], attachments: string[]} $mail_data An array containing the email recipient(s), subject, message, headers, and attachments.
+	 *
+	 * @return void
+	 */
+	public function log_success( array $mail_data ): void {
+		if ( $this->logger ) {
+			$this->logger->info( 'Mail sent', $mail_data );
+		}
+	}
+
+	/**
+	 * Log failure happening when sending mails.
+	 *
+	 * @param  WP_Error $error The error sent.
+	 *
+	 * @return void
+	 */
+	public function log_failure( WP_Error $error ): void {
+		if ( $this->logger ) {
+			/**
+			 * Mail data.
+			 *
+			 * @var array
+			 */
+			$mail_data = $error->get_error_data();
+			$this->logger->error( $error->get_error_message(), $mail_data );
+		}
+	}
 }