<?php

/**
 * Class MC4WP_Debug_Log_Reader
 */
class MC4WP_Debug_Log_Reader
{
    /**
     * @var resource|null
     */
    private $handle;

    /**
     * @var string
     */
    private static $regex = '/^(\[[\d \-\:]+\]) (\w+\:) (.*)$/S';

    /**
     * @var string
     */
    private static $html_template = '<span class="time">$1</span> <span class="level">$2</span> <span class="message">$3</span>';

    /**
     * @var string The log file location.
     */
    private $file;

    /**
     * MC4WP_Debug_Log_Reader constructor.
     *
     * @param $file
     */
    public function __construct($file)
    {
        $this->file = $file;
    }

    /**
     * @return string
     */
    public function all()
    {
        return file_get_contents($this->file);
    }

    /**
     * Sets file pointer to $n of lines from the end of file.
     *
     * @param int $n
     */
    private function seek_line_from_end($n)
    {
        $line_count = 0;

        // get line count
        while (! feof($this->handle)) {
            fgets($this->handle);
            ++$line_count;
        }

        // rewind to beginning
        rewind($this->handle);

        // calculate target
        $target  = $line_count - $n;
        $target  = $target > 1 ? $target : 1; // always skip first line because oh PHP header
        $current = 0;

        // keep reading until we're at target
        while ($current < $target) {
            fgets($this->handle);
            ++$current;
        }
    }

    /**
     * @return string|null
     */
    public function read()
    {

        // open file if not yet opened
        if (! is_resource($this->handle)) {
            // doesn't exist?
            if (! file_exists($this->file)) {
                return null;
            }

            $this->handle = @fopen($this->file, 'r'); // phpcs:ignore 

            // unable to read?
            if (! is_resource($this->handle)) {
                return null;
            }

            // set pointer to 1000 lines from EOF
            $this->seek_line_from_end(1000);
        }

        // stop reading once we're at the end
        if (feof($this->handle)) {
            fclose($this->handle); // phpcs:ignore 
            $this->handle = null;
            return null;
        }

        $text = fgets($this->handle);
        if ($text === false) {
            return null;
        }
        return trim($text);
    }

    /**
     * @return null|string
     */
    public function read_as_html()
    {
        $line = $this->read();

        // null means end of file
        if (null === $line) {
            return null;
        }

        // empty string means empty line, but not yet eof
        if ('' === $line) {
            return '';
        }

        return preg_replace(self::$regex, self::$html_template, $line);
    }
}