PHP INI parser with environment based reading

Config.php

<?php

class Config
{
    private static $environments = ['dev', 'qa', 'prod'];
    private static $filenames    = ['assets', 'libraries'];
    private static $filepath     = "/";
    private static $environment  = NULL;
    private static $file_data    = NULL;

    /**
     * Get current Environment (default 'dev')
     *
     * @return string Environment
     */
    public static function getEnvironment()
    {
        if (!isset($_SERVER['APPLICATION_ENV'])) {
            $_SERVER['APPLICATION_ENV'] = "dev";
        }

        if (!in_array($_SERVER['APPLICATION_ENV'], self::$environments)) {
            $_SERVER['APPLICATION_ENV'] = "dev";
        }

        return self::$environment = $_SERVER['APPLICATION_ENV'];
    }

    /**
     * Check the environment
     *
     * @param  string  $env Environment to check
     *
     * @return boolean
     */
    public static function isEnvironment($env)
    {
        return (self::getEnvironment() === $env) ? TRUE : FALSE;
    }

    /**
     * Read / Parse the ini file
     *
     * @param  string $filename
     *
     * @return array
     */
    public static function read($filename)
    {
        if (is_null(self::$environment)) {
            self::getEnvironment();
        }

        return self::$file_data[$filename] = parse_ini_file(self::$filepath . "$filename." . self::$environment . ".ini", TRUE);
    }

    /**
     * Get value for the key searched for
     *
     * @param  string $search_key
     *
     * @return string value
     */
    public static function get($search_key)
    {
        $search_key_array = explode('.', $search_key);

        if (count($search_key_array) != 3) {
            throw new Exception("Invalid search key");
        }

        list($filename, $section, $key) = $search_key_array;

        if (!in_array($filename, self::$filenames)) {
            throw new Exception("Invalid file to search");
        }

        if (is_null(self::$file_data) || !isset(self::$file_data[$filename])) {
            self::read($filename);
        }

        if (self::$file_data === FALSE) {
            throw new Exception("File read error");
        }

        return isset(self::$file_data[$filename][$section][$key]) ? self::$file_data[$filename][$section][$key] : NULL;
    }
}