<?php

class IP
{
    private static $ip     = NULL;
    private static $fp     = NULL;
    private static $offset = NULL;
    private static $index  = NULL;
    private static $cached = array();
    public static function find($ip)
    {
        if (empty($ip) === TRUE)
        {
            return 'N/A';
        }
        $nip   = gethostbyname($ip);
        $ipdot = explode('.', $nip);
        if ($ipdot[0] < 0 || $ipdot[0] > 255 || count($ipdot) !== 4)
        {
            return 'N/A';
        }
        if (isset(self::$cached[$nip]) === TRUE)
        {
            return self::$cached[$nip];
        }
        if (self::$fp === NULL)
        {
            self::init();
        }
        $nip2 = pack('N', ip2long($nip));
        $tmp_offset = (int)$ipdot[0] * 4;
        $start      = unpack('Vlen', self::$index[$tmp_offset] . self::$index[$tmp_offset + 1] . self::$index[$tmp_offset + 2] . self::$index[$tmp_offset + 3]);
        $index_offset = $index_length = NULL;
        $max_comp_len = self::$offset['len'] - 1024 - 4;
        for ($start = $start['len'] * 8 + 1024; $start < $max_comp_len; $start += 8)
        {
            if (self::$index[$start] . self::$index[$start + 1] . self::$index[$start + 2] . self::$index[$start + 3] >= $nip2)
            {
                $index_offset = unpack('Vlen', self::$index[$start + 4] . self::$index[$start + 5] . self::$index[$start + 6] . "\x0");
                $index_length = unpack('Clen', self::$index[$start + 7]);
                break;
            }
        }
        if ($index_offset === NULL)
        {
            return 'N/A';
        }
        fseek(self::$fp, self::$offset['len'] + $index_offset['len'] - 1024);
        self::$cached[$nip] = explode("\t", fread(self::$fp, $index_length['len']));
        return self::$cached[$nip];
    }
    private static function init()
    {
        if (self::$fp === NULL)
        {
            self::$ip = new self();
            self::$fp = fopen(__DIR__ . '/17monipdb.dat', 'rb');
            if (self::$fp === FALSE)
            {
                throw new \Exception('Invalid 17monipdb.dat file!');
            }
            self::$offset = unpack('Nlen', fread(self::$fp, 4));
            if (self::$offset['len'] < 4)
            {
                throw new \Exception('Invalid 17monipdb.dat file!');
            }
            self::$index = fread(self::$fp, self::$offset['len'] - 4);
        }
    }
    public function __destruct()
    {
        if (self::$fp !== NULL)
        {
            fclose(self::$fp);
        }
    }
}