Full Email Log With Search, Viewer and Resend

$wpide_mlog_days  = 30; // Days to keep entries.
$wpide_mlog_state = new stdClass();
$wpide_mlog_state->id = 0;

add_action( 'admin_init', function () {
    global $wpdb;

    if ( '1' === get_option( 'wpide_mail_log_db' ) || ! current_user_can( 'manage_options' ) ) {
        return;
    }

    require_once ABSPATH . 'wp-admin/includes/upgrade.php';
    dbDelta( "CREATE TABLE {$wpdb->prefix}wpide_mail_log (
        id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
        sent_at datetime NOT NULL,
        to_addr text NOT NULL,
        subject text NOT NULL,
        headers text NOT NULL,
        message longtext NOT NULL,
        status varchar(20) NOT NULL DEFAULT 'queued',
        error text NOT NULL,
        PRIMARY KEY  (id),
        KEY sent_at (sent_at)
    ) {$wpdb->get_charset_collate()};" );

    update_option( 'wpide_mail_log_db', '1', true );
} );

add_filter( 'wp_mail', function ( $atts ) use ( $wpide_mlog_state ) {
    global $wpdb;

    if ( '1' !== get_option( 'wpide_mail_log_db' ) ) {
        return $atts;
    }

    $wpdb->insert( $wpdb->prefix . 'wpide_mail_log', array(
        'sent_at' => current_time( 'mysql', true ),
        'to_addr' => implode( ', ', (array) $atts['to'] ),
        'subject' => (string) $atts['subject'],
        'headers' => is_array( $atts['headers'] ) ? implode( "\n", $atts['headers'] ) : (string) $atts['headers'],
        'message' => (string) $atts['message'],
        'status'  => 'queued',
        'error'   => '',
    ) );
    $wpide_mlog_state->id = (int) $wpdb->insert_id;

    return $atts;
}, PHP_INT_MAX );

add_action( 'wp_mail_succeeded', function () use ( $wpide_mlog_state ) {
    global $wpdb;
    if ( $wpide_mlog_state->id ) {
        $wpdb->update( $wpdb->prefix . 'wpide_mail_log', array( 'status' => 'sent' ), array( 'id' => $wpide_mlog_state->id ) );
        $wpide_mlog_state->id = 0;
    }
} );

add_action( 'wp_mail_failed', function ( $error ) use ( $wpide_mlog_state ) {
    global $wpdb;
    if ( $wpide_mlog_state->id ) {
        $wpdb->update( $wpdb->prefix . 'wpide_mail_log', array( 'status' => 'failed', 'error' => $error->get_error_message() ), array( 'id' => $wpide_mlog_state->id ) );
        $wpide_mlog_state->id = 0;
    }
} );

add_action( 'init', function () {
    if ( ! wp_next_scheduled( 'wpide_mail_log_purge' ) ) {
        wp_schedule_event( time() + HOUR_IN_SECONDS, 'daily', 'wpide_mail_log_purge' );
    }
} );

add_action( 'wpide_mail_log_purge', function () use ( $wpide_mlog_days ) {
    global $wpdb;
    if ( '1' === get_option( 'wpide_mail_log_db' ) ) {
        $wpdb->query( $wpdb->prepare( "DELETE FROM {$wpdb->prefix}wpide_mail_log WHERE sent_at < %s", gmdate( 'Y-m-d H:i:s', time() - $wpide_mlog_days * DAY_IN_SECONDS ) ) );
    }
} );

add_action( 'admin_menu', function () {
    add_management_page( 'Mail Log', 'Mail Log', 'manage_options', 'wpide-mail-log', function () {
        global $wpdb;
        $table = $wpdb->prefix . 'wpide_mail_log';
        $base  = admin_url( 'tools.php?page=wpide-mail-log' );

        echo '<div class="wrap"><h1>Mail Log</h1>';

        if ( '1' !== get_option( 'wpide_mail_log_db' ) ) {
            echo '<p>The log table is being created. Reload this page.</p></div>';
            return;
        }

        // Actions.
        if ( isset( $_GET['resend'] ) && check_admin_referer( 'wpide_mlog_resend' ) ) {
            $row = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM {$table} WHERE id = %d", absint( $_GET['resend'] ) ) );
            if ( $row ) {
                $ok = wp_mail( array_map( 'trim', explode( ',', $row->to_addr ) ), $row->subject, $row->message, array_filter( explode( "\n", $row->headers ) ) );
                printf( '<div class="notice notice-%s"><p>%s</p></div>', $ok ? 'success' : 'error', $ok ? 'Email resent.' : 'The email could not be resent.' );
            }
        }
        if ( isset( $_POST['wpide_mlog_clear'] ) && check_admin_referer( 'wpide_mlog_clear' ) ) {
            $wpdb->query( "DELETE FROM {$table}" ); // phpcs:ignore
            echo '<div class="notice notice-success"><p>Log cleared.</p></div>';
        }

        // Single message view.
        if ( isset( $_GET['view'] ) ) {
            $row = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM {$table} WHERE id = %d", absint( $_GET['view'] ) ) );
            if ( $row ) {
                printf( '<p><a href="%s">← Back to the log</a></p>', esc_url( $base ) );
                printf( '<table class="widefat striped"><tbody><tr><th>To</th><td>%s</td></tr><tr><th>Subject</th><td>%s</td></tr><tr><th>Date (UTC)</th><td>%s</td></tr><tr><th>Status</th><td>%s %s</td></tr><tr><th>Headers</th><td><pre style="white-space:pre-wrap">%s</pre></td></tr></tbody></table>', esc_html( $row->to_addr ), esc_html( $row->subject ), esc_html( $row->sent_at ), esc_html( $row->status ), esc_html( $row->error ), esc_html( $row->headers ) );
                echo '<h2>Message</h2><iframe sandbox="" style="width:100%;min-height:420px;background:#fff;border:1px solid #c3c4c7" srcdoc="' . esc_attr( false !== stripos( $row->message, '<html' ) || false !== stripos( $row->headers, 'text/html' ) ? $row->message : '<pre style="white-space:pre-wrap;font:14px/1.5 sans-serif">' . esc_html( $row->message ) . '</pre>' ) . '"></iframe>';
                printf( '<p><a class="button" href="%s">Resend this email</a></p></div>', esc_url( wp_nonce_url( add_query_arg( 'resend', (int) $row->id, $base ), 'wpide_mlog_resend' ) ) );
                return;
            }
        }

        $search = isset( $_GET['s'] ) ? sanitize_text_field( wp_unslash( $_GET['s'] ) ) : '';
        $paged  = max( 1, isset( $_GET['paged'] ) ? absint( $_GET['paged'] ) : 1 );
        $where  = $search ? $wpdb->prepare( 'WHERE to_addr LIKE %s OR subject LIKE %s', '%' . $wpdb->esc_like( $search ) . '%', '%' . $wpdb->esc_like( $search ) . '%' ) : '';
        $rows   = $wpdb->get_results( "SELECT id, sent_at, to_addr, subject, status FROM {$table} {$where} ORDER BY id DESC LIMIT 50 OFFSET " . ( ( $paged - 1 ) * 50 ) ); // phpcs:ignore

        printf( '<form method="get"><input type="hidden" name="page" value="wpide-mail-log"><p class="search-box"><input type="search" name="s" value="%s" placeholder="Recipient or subject"> <button class="button">Search</button></p></form>', esc_attr( $search ) );
        echo '<table class="widefat striped"><thead><tr><th>Date (UTC)</th><th>To</th><th>Subject</th><th>Status</th><th></th></tr></thead><tbody>';
        if ( ! $rows ) {
            echo '<tr><td colspan="5">No emails logged yet.</td></tr>';
        }
        foreach ( $rows as $row ) {
            printf( '<tr><td>%s</td><td>%s</td><td>%s</td><td>%s</td><td><a href="%s">View</a></td></tr>', esc_html( $row->sent_at ), esc_html( $row->to_addr ), esc_html( $row->subject ), esc_html( $row->status ), esc_url( add_query_arg( 'view', (int) $row->id, $base ) ) );
        }
        echo '</tbody></table>';
        if ( 50 === count( $rows ) ) {
            printf( '<p><a class="button" href="%s">Older emails →</a></p>', esc_url( add_query_arg( array( 'paged' => $paged + 1, 's' => $search ), $base ) ) );
        }
        echo '<form method="post" style="margin-top:1em">';
        wp_nonce_field( 'wpide_mlog_clear' );
        echo '<button class="button button-link-delete" name="wpide_mlog_clear" value="1" onclick="return confirm(\'Delete all log entries?\')">Clear the log</button></form></div>';
    } );
} );