package cidr

import (
	"bytes"
	"fmt"
	"math"
	"net"
	"sort"
)

// SuperNetting 合并网段
func SuperNetting(ns []string) (*cidr, error) {
	num := len(ns)
	if num < 1 || (num&(num-1)) != 0 {
		return nil, fmt.Errorf("子网数量必须是2的次方")
	}

	mask := ""
	var cidrs []*cidr
	for _, n := range ns {
		// 检查子网CIDR有效性
		c, err := ParseCIDR(n)
		if err != nil {
			return nil, fmt.Errorf("网段%v格式错误", n)
		}
		cidrs = append(cidrs, c)

		// TODO 暂只考虑相同子网掩码的网段合并
		if len(mask) == 0 {
			mask = c.Mask()
		} else if c.Mask() != mask {
			return nil, fmt.Errorf("子网掩码不一致")
		}
	}
	AscSortCIDRs(cidrs)

	// 检查网段是否连续
	var network net.IP
	for _, c := range cidrs {
		if len(network) > 0 {
			if !network.Equal(c.ipNet.IP) {
				return nil, fmt.Errorf("必须是连续的网段")
			}
		}
		network = net.ParseIP(c.Broadcast())
		IncrIP(network)
	}

	// 子网掩码左移，得到共同的父网段
	c := cidrs[0]
	ones, bits := c.MaskSize()
	ones = ones - int(math.Log2(float64(num)))
	c.ipNet.Mask = net.CIDRMask(ones, bits)
	c.ipNet.IP.Mask(c.ipNet.Mask)

	return c, nil
}

// IncrIP IP地址自增
func IncrIP(ip net.IP) {
	for i := len(ip) - 1; i >= 0; i-- {
		ip[i]++
		if ip[i] > 0 {
			break
		}
	}
}

// DecrIP IP地址自减
func DecrIP(ip net.IP) {
	length := len(ip)
	for i := length - 1; i >= 0; i-- {
		ip[length-1]--
		if ip[length-1] < 0xFF {
			break
		}
		for j := 1; j < length; j++ {
			ip[length-j-1]--
			if ip[length-j-1] < 0xFF {
				return
			}
		}
	}
}

// Compare 比较IP大小 a等于b，返回0; a大于b，返回+1; a小于b，返回-1
func Compare(a, b net.IP) int {
	return bytes.Compare(a, b)
}

// AscSortCIDRs 升序
func AscSortCIDRs(cs []*cidr) {
	sort.Slice(cs, func(i, j int) bool {
		if n := bytes.Compare(cs[i].ipNet.IP, cs[j].ipNet.IP); n != 0 {
			return n < 0
		}

		if n := bytes.Compare(cs[i].ipNet.Mask, cs[j].ipNet.Mask); n != 0 {
			return n < 0
		}

		return false
	})
}

// DescSortCIDRs 降序
func DescSortCIDRs(cs []*cidr) {
	sort.Slice(cs, func(i, j int) bool {
		if n := bytes.Compare(cs[i].ipNet.IP, cs[j].ipNet.IP); n != 0 {
			return n >= 0
		}

		if n := bytes.Compare(cs[i].ipNet.Mask, cs[j].ipNet.Mask); n != 0 {
			return n >= 0
		}

		return false
	})
}