Add user last seen information

security.php

@@ -16,6 +16,10 @@
 require_once __DIR__ . '/security/login-error.php';
 require_once __DIR__ . '/security/password.php';
 
+if ( defined( 'VIP_USER_LAST_SEEN_ENABLED' ) ) {
+	require_once __DIR__ . '/security/user-last-seen.php';
+}
+
 use Automattic\VIP\Utils\Context;
 
 define( 'CACHE_GROUP_LOGIN_LIMIT', 'vip_login_limit' );

security/user-last-seen.php

@@ -0,0 +1,60 @@
+<?php
+
+const LAST_SEEN_UPDATE_USER_META_CACHE_TTL = 60; // Store last seen once per minute to avoid too much write DB operations
+const LAST_SEEN_UPDATE_USER_META_CACHE_KEY_PREFIX = 'vip_last_seen_update_user_meta_cache_key';
+
+add_action( 'set_current_user', 'update_user_last_seen', 10, 0 );
+add_filter ('manage_users_columns', 'users_columns' ) ;
+add_filter ('manage_users_custom_column', 'users_custom_column', 10, 3 ) ;
+
+function update_user_last_seen() {
+	global $current_user;
+
+	$cache_key = LAST_SEEN_UPDATE_USER_META_CACHE_KEY_PREFIX . $current_user->ID;
+
+	try {
+		if ( wp_cache_get( $cache_key ) ) {
+			return;
+		}
+
+		update_user_meta( $current_user->ID, 'vip_last_seen', time() );
+
+		wp_cache_set( $cache_key, true, null, LAST_SEEN_UPDATE_USER_META_CACHE_TTL );
+	} catch ( \Exception $e ) {
+		trigger_error(
+			sprintf( 'failed to update user last seen meta', esc_html( $e->getMessage() ) ),
+			E_USER_WARNING
+		);
+	}
+}
+
+function users_columns ($cols) {
+	$cols['last_seen'] = __( 'Last seen' ) ;
+	return $cols;
+}
+
+function users_custom_column ( $default, $column_name, $user_id ) {
+	if ( 'last_seen' == $column_name ) {
+		$last_seen_timestamp = get_user_meta( $user_id, 'vip_last_seen', true );
+
+		if ( $last_seen_timestamp ) {
+			$formatted_date = sprintf(
+				__( '%1$s at %2$s' ),
+				date_i18n( get_option('date_format'), $last_seen_timestamp ),
+				date_i18n( get_option('time_format'), $last_seen_timestamp )
+			);
+
+			if ( defined( 'VIP_CONSIDER_USERS_INACTIVE_AFTER_DAYS' ) ) {
+				$diff = ( new DateTime( sprintf('@%s', $last_seen_timestamp ) ) )->diff( new DateTime() );
+
+				if ( $diff->days >= constant( 'VIP_CONSIDER_USERS_INACTIVE_AFTER_DAYS' ) ) {
+					return sprintf( '<span class="wp-ui-text-notification">%s</span>', esc_html__( $formatted_date ) );
+				}
+			}
+
+			return sprintf( '<span>%s</span>', esc_html__( $formatted_date ) );
+		}
+	}
+
+	return $default;
+}