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<?php
class UserAgentStringParser
{
    /**
     * Extracts information from the user agent string.
     *
     * @param string $string The user agent string
     * @return array Returns the user agent information.
     */
    public function parse($string)
    {
        $userAgent = array(
            'string' => $this->cleanUserAgentString($string),
            'browser_name' => null,
            'browser_version' => null
        );

        if (empty($userAgent['string'])) {
            return $userAgent;
        }

        // Find the right name/version phrase (or return empty array if none found)
        foreach ($this->getKnownBrowsers() as $browser => $regex) {
            // Build regex that matches phrases for known browsers (e.g. "Firefox/2.0" or "MSIE 6.0").
            // This only matches the major and minor version numbers (e.g. "2.0.0.6" is parsed as simply "2.0").
            $pattern = '#'.$regex.'[/ ]+([0-9]+(?:\.[0-9]+)?)#';

            if (preg_match($pattern, $userAgent['string'], $matches)) {
                $userAgent['browser_name'] = $browser;

                if (isset($matches[1])) {
                    $userAgent['browser_version'] = $matches[1];
                }

                break;
            }
        }

        return $userAgent;
    }

    /**
     * Gets known browsers. Since some UAs have more than one phrase we use an ordered array to define the precedence.
     *
     * @return string[]
     */
    protected function getKnownBrowsers()
    {
        return array(
            'firefox' => 'firefox',
            'opera' => 'opera',
            'edge' => 'edge',
            'msie' => 'msie',
            'chrome' => 'chrome',
            'safari' => 'safari',
            // ...
        );
    }

    /**
     * Gets known browser aliases.
     *
     * @return array
     */
    protected function getKnownBrowserAliases()
    {
        return array(
            'opr' => 'opera',
            'iceweasel' => 'firefox',
            // ...
        );
    }

    /**
     * Make user agent string lowercase, and replace browser aliases.
     *
     * @param string $string The dirty user agent string
     * @return string Returns the clean user agent string.
     */
    protected function cleanUserAgentString($string)
    {
        // clean up the string
        $string = trim(strtolower($string));

        // replace browser names with their aliases
        $string = strtr($string, $this->getKnownBrowserAliases());

        return $string;
    }
}