<?php

class DebugLog
{
    const DEBUG_FILE = '/tmp/debug.log';

    protected static $_instance;

    protected $_handle = NULL;

    protected function __construct() {
        $this->_handle = fopen($this::DEBUG_FILE, 'a+');

        if ($this->_handle === FALSE) {
            throw new Exception('Failed to open debug log!');
        }
    }

    public function __destruct() {
        //fclose($this->_handle);
    }

    public static function getInstance() {
        if(!self::$_instance instanceof self) {
            self::$_instance = new self();
        }

        return self::$_instance;
    }

    public function log($msg, $tag='')
    {
        // retrieve the backtrace and set the file & line
        $backtrace = debug_backtrace();

        $formattedBacktrace = '';
        foreach ($backtrace as $i=>$entry) {
            $formattedBacktrace.= sprintf('#%-2d | %-4s | %-30s | %s'. PHP_EOL, $i, $entry['line'], $entry['function'], $entry['file']);
        }

        // get the currently formatted time
        $time = date('Ymd H:i:s');

        // format the tags
        if (!empty($tag)) {
            if (is_array($tag)) {
                $tag = implode(',', $tag);
            }
        }

        // format the start line
        $preamble = sprintf('-------------- %s tags(%s) --------------', $time, $tag);

        // format the message
        if (is_array($msg) || is_object($msg)) {
            $msg = print_r($msg, TRUE);
        }

        $hr = '----------';

        // log the message
        if (fwrite($this->_handle, $preamble. PHP_EOL. $msg. PHP_EOL. $hr. PHP_EOL. $formattedBacktrace) === FALSE) {
            throw new Exception('Failed to write to debug log.');
        }

        return $this;
    }

}