/*
 Copyright 2022 The Hybridnet Authors.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
*/

package utils

import (
	"math/big"
	"net"
)

// NextIP returns IP incremented by 1, if IP is invalid, return nil
func NextIP(ip net.IP) net.IP {
	normalizedIP := normalizeIP(ip)
	if normalizedIP == nil {
		return nil
	}

	i := ipToInt(normalizedIP)
	return intToIP(i.Add(i, big.NewInt(1)), len(normalizedIP) == net.IPv6len)
}

// PrevIP returns IP decremented by 1, if IP is invalid, return nil
func PrevIP(ip net.IP) net.IP {
	normalizedIP := normalizeIP(ip)
	if normalizedIP == nil {
		return nil
	}

	i := ipToInt(normalizedIP)
	return intToIP(i.Sub(i, big.NewInt(1)), len(normalizedIP) == net.IPv6len)
}

// Cmp compares two IPs, returning the usual ordering:
// a < b : -1
// a == b : 0
// a > b : 1
// incomparable : -2
func Cmp(a, b net.IP) int {
	normalizedA := normalizeIP(a)
	normalizedB := normalizeIP(b)

	if len(normalizedA) == len(normalizedB) && len(normalizedA) != 0 {
		return ipToInt(normalizedA).Cmp(ipToInt(normalizedB))
	}

	return -2
}

// Capacity returns the absolute number of IPs between a and b.
// 0 is returned if a and b are of different IP families, or
// any of those two IPs is invalid.
func Capacity(a, b net.IP) *big.Int {
	normalizedA := normalizeIP(a)
	normalizedB := normalizeIP(b)

	if normalizedA == nil || normalizedB == nil || len(normalizedA) != len(normalizedB) {
		return big.NewInt(0)
	}

	ai := ipToInt(normalizedA)
	bi := ipToInt(normalizedB)

	return big.NewInt(0).Add(
		big.NewInt(0).Abs(
			big.NewInt(0).Sub(bi, ai),
		), big.NewInt(1),
	)
}

func ipToInt(ip net.IP) *big.Int {
	return big.NewInt(0).SetBytes(ip)
}

func intToIP(i *big.Int, isIPv6 bool) net.IP {
	intBytes := i.Bytes()

	if len(intBytes) == net.IPv4len || len(intBytes) == net.IPv6len {
		return intBytes
	}

	if isIPv6 {
		return append(make([]byte, net.IPv6len-len(intBytes)), intBytes...)
	}

	return append(make([]byte, net.IPv4len-len(intBytes)), intBytes...)
}

// normalizeIP will normalize IP by family,
// IPv4 : 4-byte form
// IPv6 : 16-byte form
// others : nil
func normalizeIP(ip net.IP) net.IP {
	if ipTo4 := ip.To4(); ipTo4 != nil {
		return ipTo4
	}
	return ip.To16()
}

// Network masks off the host portion of the IP, if IPNet is invalid,
// return nil
func Network(ipn *net.IPNet) *net.IPNet {
	if ipn == nil {
		return nil
	}

	maskedIP := ipn.IP.Mask(ipn.Mask)
	if maskedIP == nil {
		return nil
	}

	return &net.IPNet{
		IP:   maskedIP,
		Mask: ipn.Mask,
	}
}
