package netsplit

import (
	"net/netip"

	"go4.org/netipx"
)

/*
	Split splits the network defined in a CIDRSplitter alongside its configuration and performs the subnetting.
	This strategy attempts to split a network into subnets of a single uniform explicit size.
*/
func (c *CIDRSplitter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {

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

	if c == nil || c.PrefixLength == 0 || c.BaseSplitter == nil || c.network == nil {
		return
	}

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

	if c.PrefixLength < uint8(base.Bits()) {
		err = ErrBigPrefix
		return
	}

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

	for {
		if sub, remaining, ok = remaining.RemoveFreePrefix(c.PrefixLength); !ok {
			if !sub.IsValid() {
				// No error; it's literally impossible since we network on boundaries.
				// We just hit the end of the prefix.
				break
			}
		}
		subPtr = new(netip.Prefix)
		*subPtr = sub
		nets = append(nets, subPtr)
	}

	return
}