package netsplit

import (
	"go4.org/netipx"
	"net/netip"
	"sort"
)

// Split splits the network defined in a VLSMSplitter alongside its configuration and performs the subnetting.
func (v *VLSMSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {

	var ok bool
	var pfxLen int
	var pfxLen8 uint8
	var base netip.Prefix
	var sub netip.Prefix
	var subPtr *netip.Prefix
	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)

	if err = ValidateSizes(v.network, v.PrefixLengths...); err != nil {
		return
	}

	/*
		I thought about using the following:

			* https://pkg.go.dev/net/netip
			* https://pkg.go.dev/github.com/sacloud/packages-go/cidr
			* https://pkg.go.dev/github.com/projectdiscovery/mapcidr
			* https://pkg.go.dev/github.com/EvilSuperstars/go-cidrman

		But, as I expected, netipx ftw again.
	*/

	if v == nil || v.PrefixLengths == nil || len(v.PrefixLengths) == 0 || v.BaseSplitter == nil || v.network == nil {
		return
	}

	sort.SliceStable(
		v.PrefixLengths,
		func(i, j int) (isBefore bool) { // We use a reverse sorting by default so we get larger prefixes at the beginning.
			if v.Ascending {
				isBefore = v.PrefixLengths[i] > v.PrefixLengths[j]
			} else {
				isBefore = v.PrefixLengths[i] < v.PrefixLengths[j]
			}
			return
		},
	)

	pfxLen, _ = v.network.Mask.Size()
	pfxLen8 = uint8(pfxLen)

	if base, ok = netipx.FromStdIPNet(v.network); !ok {
		err = ErrBadBoundary
		return
	}
	if !base.IsValid() {
		err = ErrBadBoundary
		return
	}

	ipsb.AddPrefix(base)
	if remaining, err = ipsb.IPSet(); err != nil {
		return
	}

	for _, size := range v.PrefixLengths {
		if size < pfxLen8 {
			err = &SplitErr{
				Wrapped:            ErrBigPrefix,
				Nets:               nets,
				Remaining:          remaining,
				LastSubnet:         &sub,
				RequestedPrefixLen: size,
			}
			return
		}

		if sub, remaining, ok = remaining.RemoveFreePrefix(size); !ok {
			err = &SplitErr{
				Wrapped:            ErrNoNetSpace,
				Nets:               nets,
				Remaining:          remaining,
				LastSubnet:         &sub,
				RequestedPrefixLen: size,
			}
			return
		}

		subPtr = new(netip.Prefix)
		*subPtr = sub
		nets = append(nets, subPtr)
	}

	return
}