package common

import (
	"crypto/rand"
	"encoding/binary"
	"fmt"
	"math/big"
	"net"
)

func iptouint(ip net.IP) uint32 {
	ip = ip.To4()
	return uint32(ip[0])<<24 | uint32(ip[1])<<16 | uint32(ip[2])<<8 | uint32(ip[3])
}

func toip(num uint32) string {
	return fmt.Sprintf("%d.%d.%d.%d",
		(num>>24)&255,
		(num>>16)&255,
		(num>>8)&255,
		num&255)
}

func seed() int64 {
	var n int64
	if err := binary.Read(rand.Reader, binary.LittleEndian, &n); err != nil {
		return 1337
	}
	return n
}

// per-cidr linear congruential generator for efficient randomized target ip ordering, ty claude
func LCG(cidr string, out chan<- string) {
	// lcg constants
	const a uint64 = 1664525
	const c uint64 = 1013904223

	_, ipnet, _ := net.ParseCIDR(cidr)
	start := iptouint(ipnet.IP)
	ones, bits := ipnet.Mask.Size()
	addrcount := new(big.Int).Lsh(big.NewInt(1), uint(bits-ones))

	x := uint64(seed()) ^ uint64(start) // seed for unique randomization per execution
	m := uint64(addrcount.Uint64())

	for i := uint64(0); i < m; i++ {
		x = (a*x + c) % (1 << 32) // mod of full 32bit addr count
		ip := toip(uint32((x % m) + uint64(start)))
		out <- ip
	}
}