Simple static logger class for logging errors. Provides convenience logging methods, date stamping the log file, getting call source and specifying log location.

logger.php

<?php

class Logger {
	private static $timestamp = 'Y-m-d H:i:s';
	
	private static $logFileNameFormat = 'Y-m-d';
	private static $logDirLocation = __DIR__;
	
	private static $logLevels = ['DEBUG', 'INFO', 'WARN', 'ERROR'];
	private static $minLogLevel = 'INFO';
	

	private function __construct() {
		// Prevent instantiation
	}


	/**
	 * Easy accessor functions
	 */
	public static function logDebug($message) {
		self::log($message, self::$logLevels[0]);
	}


	public static function logInfo($message) {
		self::log($message, self::$logLevels[1]);
	}


	public static function logWarning($message) {
		self::log($message, self::$logLevels[2]);
	}


	public static function logError($message) {
		self::log($message, self::$logLevels[3]);
	}


	/**
	 * Get the name of the file that is calling on the log functionality and return it. 
	 * This might directly calling the log() function or one of the helper methods so we have
	 * to look for the first file that is not the local file.
	 *
	 * @return string
	 */
	private static function getCallSource() {
        $backtrace = debug_backtrace(FALSE, 3);
        $levelsDeep = count($backtrace);

		if ($levelsDeep > 0) {
			foreach ($backtrace as $traceLevel) {
                if (isset($traceLevel['file']) && strtolower($traceLevel['file']) != strtolower(__FILE__)) {
                    return $traceLevel['file'];
                }
            }
		}

		return '';
	}


	private static function getLogLevel($level) {
		if (($level != null) && in_array(strtoupper($level), self::$logLevels)) {
			return $level;
		} else {
			return self::$minLogLevel;
		}
	}


	private static function isLocationWritable() {
		return is_writable(self::$logDirLocation);
	}


	public static function setDirectoryLocation($dirPath) {
		if (is_string($dirPath)) {
			$path = realpath($dirPath);

			if (is_dir($path)) {
				self::$logDirLocation = $path;
				return true;
			}
		}

		return false;
	}


	private static function openLog($filePath) {
		$f = fopen($filePath, 'a');

		if ($f !== false) {
			return $f;
		}

		return false;
	}


	public static function log($message, $level = null) {
		if (is_string($message) && (trim($message) != '')) {
			if (self::isLocationWritable()) {
				$logTimestamp = date(self::$timestamp);
				$callingSource = self::getCallSource();
				$logLevel = self::getLogLevel($level);
				$filePath = self::$logDirLocation . '/' . date(self::$logFileNameFormat) . '.log';

				$handle = self::openLog($filePath);

				if ($handle !== false) {
					fwrite($handle, "[{$logLevel}]\t[{$logTimestamp}] {$message} - Source: {$callingSource}" . PHP_EOL);
					fclose($handle);
				} else {
					throw new Exception('Unable to open log file for writing.');
				}
			} else {
				throw new Exception('Unable to write to log file. Write permission to this file location is denied.');
			}
		}
	}
}