package io.trygvis.rules.network;

import java.util.regex.Pattern;

public class IpCalc {
    private static final Pattern pattern = Pattern.compile("([0-9]{1,3})\\.([0-9]{1,3})\\.([0-9]{1,3})\\.([0-9]{1,3})/([0-9]{1,3})");

    public static Ipv4Cidr cidr(String cidr) {
        var matcher = pattern.matcher(cidr);
        if (!matcher.matches()) {
            throw new IllegalArgumentException("Not a CIDR: " + cidr);
        }

        var b1 = matcher.group(1);
        var b2 = matcher.group(2);
        var b3 = matcher.group(3);
        var b4 = matcher.group(4);

        int network = parse(b1) << 24 |
                parse(b2) << 16 |
                parse(b3) << 8 |
                parse(b4);

//        System.out.printf("network = %x%n", network);

        var l = matcher.group(5);
        var bits = Integer.parseInt(l);
        var hostBits = 32 - bits;
        int size = 1 << hostBits;

        int netmask = (-1 >> hostBits) << hostBits;
//        System.out.printf("netmask = %08x%n", netmask);

        int x = network & ~netmask;

        if (x != 0) {
            throw new IllegalArgumentException("Not a CIDR: " + cidr);
        }

        return new Ipv4Cidr(network, netmask, size, bits);
    }

    private static int parse(String s) {
        var i = Integer.parseInt(s);
        if (i > 255) {
            throw new IllegalArgumentException("Not a CIDR");
        }

        return i;
    }
}