woocommerce/includes/abstracts/abstract-wc-log-handler.php

<?php
if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly
}

/**
 * Abstract WC Log Handler Class
 *
 * @version        1.0.0
 * @package        WooCommerce/Abstracts
 * @category       Abstract Class
 * @author         WooThemes
 */
abstract class WC_Log_Handler implements WC_Log_Handler_Interface {

	/**
	 * Formats a timestamp for use in log messages.
	 *
	 * @param int $timestamp Log timestamp.
	 * @return string Formatted time for use in log entry.
	 */
	protected static function format_time( $timestamp ) {
		return date( 'c', $timestamp );
	}

	/**
	 * Builds a log entry text from level, timestamp and message.
	 *
	 * @param int $timestamp Log timestamp.
	 * @param string $level emergency|alert|critical|error|warning|notice|info|debug
	 * @param string $message Log message.
	 * @param array $context Additional information for log handlers.
	 *
	 * @return string Formatted log entry.
	 */
	protected static function format_entry( $timestamp, $level, $message, $context ) {
		$time_string = self::format_time( $timestamp );
		$level_string = strtoupper( $level );
		$entry = "{$time_string} {$level_string} {$message}";

		return apply_filters( 'woocommerce_format_log_entry', $entry, array(
			'timestamp' => $timestamp,
			'level' => $level,
			'message' => $message,
			'context' => $context,
		) );
	}
}