package netsplit

import (
	`net`
	"net/netip"

	`github.com/projectdiscovery/mapcidr`
	"go4.org/netipx"
)

/*
	Split splits the network defined in a SubnetSplitter alongside its configuration and performs the subnetting.
	This strategy allows for splitting a network into exactly evenly sized specified number of subnets.

	remaining may or may not be nil depending on if the specified number of subnets fit cleanly into the network boundaries.

	An ErrNoNetSpace error will be returned if subnetting size exhaustion occurs before the specified number of subnets is reached
	(but nets will be populated and remaining will contain any left over subnets).
*/
func (s *SubnetSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {

	var ok bool
	var pfxLen int
	var base netip.Prefix
	var sub netip.Prefix
	var subPtr *netip.Prefix
	var split []*net.IPNet
	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)

	if s == nil || s.BaseSplitter == nil || s.network == nil || s.NumberSubnets == 0 {
		return
	}

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

	if split, err = mapcidr.SplitIPNetIntoN(s.network, int(s.NumberSubnets)); err != nil {
		return
	}

	for _, n := range split {
		if sub, ok = netipx.FromStdIPNet(n); !ok {
			// We bail early on this error.
			err = &SplitErr{
				Wrapped:            ErrBadBoundary,
				Nets:               nets,
				Remaining:          remaining,
				LastSubnet:         subPtr,
				RequestedPrefixLen: 0,
			}
			err = ErrBadBoundary
			return
		}
		if sub.String() == base.String() {
			continue
		}
		if pfxLen == 0 {
			pfxLen = sub.Bits()
			if nets == nil {
				nets = make([]*netip.Prefix, 0)
			}
			subPtr = new(netip.Prefix)
			*subPtr = sub
			nets = append(nets, subPtr)
		} else {
			if sub.Bits() != pfxLen {
				if err == nil {
					// Return this err but don't return early; wait for the populate.
					err = &SplitErr{
						Wrapped:            ErrNoNetSpace,
						Nets:               nets,
						Remaining:          remaining,
						LastSubnet:         subPtr,
						RequestedPrefixLen: uint8(pfxLen),
					}
				}
				ipsb.AddPrefix(sub)
			} else {
				subPtr = new(netip.Prefix)
				*subPtr = sub
				nets = append(nets, subPtr)
			}
		}
	}

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

	if len(nets) < int(s.NumberSubnets) {
		err = &SplitErr{
			Wrapped:   ErrNoNetSpace,
			Nets:      nets,
			Remaining: remaining,
		}
		return
	}

	return
}