<?php

declare(strict_types=1);

class IpUtil
{

	public static function rangeToCidr(int $start, int $end): string
	{
		$value = $start ^ $end;
		if (!self::isAllOnes($value))
			return 'NOT SUBNET: ' . long2ip($start) . '-' . long2ip($end);
		$ones = self::bitLength($value);
		return long2ip($start) . '/' . (32 - $ones);
	}

	public static function isValidSubnetRange(int $start, int $end): bool
	{
		return self::isAllOnes($start ^ $end);
	}

	/**
	 * Return number of bits required to represent
	 * this number.
	 * !! Assumes given number is 2^n - 1 !!
	 */
	private static function bitLength(int $value): int
	{
		// This is log(value) / log(2)
		// It should actually be $value + 1, but floating point errors
		// start to happen either way at higher values, so with
		// the round() thrown in, it doesn't matter...
		return (int)round(log($value) / 0.69314718055995);
	}

	/**
	 * Is the given number just ones if converted to
	 * binary (ignoring leading zeros)?
	 */
	private static function isAllOnes(int $value): bool
	{
		return ($value & ($value + 1)) === 0;
	}

	/**
	 * Parse network range in CIDR notion, return
	 * ['start' => (int), 'end' => (int)] representing
	 * the according start and end addresses as integer
	 * values. Returns false on malformed input.
	 *
	 * @param string $cidr 192.168.101/24, 1.2.3.4/16, ...
	 * @return array{start: int, end: int}|null start and end address, false on error
	 */
	public static function parseCidr(string $cidr): ?array
	{
		$parts = explode('/', $cidr);
		if (count($parts) !== 2) {
			$ip = ip2long($cidr);
			if ($ip === false)
				return null;
			return ['start' => $ip, 'end' => $ip];
		}
		$ip = $parts[0];
		$bits = $parts[1];
		if (!is_numeric($bits) || $bits < 0 || $bits > 32)
			return null;
		$dots = substr_count($ip, '.');
		if ($dots < 3) {
			$ip .= str_repeat('.0', 3 - $dots);
		}
		$ip = ip2long($ip);
		if ($ip === false)
			return null;
		$bits = (int)((2 ** (32 - $bits)) - 1);
		return ['start' => $ip & ~$bits, 'end' => $ip | $bits];
	}

}