package zones

import "net/netip"

const (
	// MaxZoneID indicates the highest ID allowed for a Zone
	MaxZoneID = 0xf
	// MaxNodeID indicates the highest Machine ID allowed within a Zone
	MaxNodeID = 0xff - 1
)

// ValidZoneID checks if the given zoneID is a valid 4 bit zone number.
//
// 0 is reserved, and only allowed when composing CIDRs.
func ValidZoneID(zoneID int) bool {
	switch {
	case zoneID < 0 || zoneID > MaxZoneID:
		return false
	default:
		return true
	}
}

// ValidNodeID checks if the given nodeID is a valid 8 bit number.
// nodeID is unique within a Zone.
// 0 is reserved, and only allowed when composing CIDRs.
func ValidNodeID(nodeID int) bool {
	switch {
	case nodeID < 0 || nodeID > MaxNodeID:
		return false
	default:
		return true
	}
}

// ParseRingZeroAddress extracts zone and node ID from a wg0 [netip.Addr]
// wg0 addresses are of the form `10.0.{{zoneID}}.{{nodeID}}`
func ParseRingZeroAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
	if addr.IsValid() {
		a4 := addr.As4()

		if a4[0] == 10 && a4[1] == 0 {
			return int(a4[2]), int(a4[3]), true
		}
	}
	return 0, 0, false
}

// RingZeroAddress returns a wg0 IP address
func RingZeroAddress(zoneID, nodeID int) (netip.Addr, bool) {
	switch {
	case !ValidZoneID(zoneID) || !ValidNodeID(nodeID):
		return netip.Addr{}, false
	default:
		a4 := [4]uint8{10, 0, uint8(zoneID), uint8(nodeID)}
		return netip.AddrFrom4(a4), true
	}
}

// ParseRingOneAddress extracts zone and node ID from a wg1 [netip.Addr]
// wg1 addresses are of the form `10.{{zoneID << 4}}.{{nodeID}}`
func ParseRingOneAddress(addr netip.Addr) (zoneID int, nodeID int, ok bool) {
	if addr.IsValid() {
		a4 := addr.As4()

		if a4[0] == 10 && a4[2] == 0 {
			zoneID = int(a4[1] >> 4)
			nodeID = int(a4[3])
			return zoneID, nodeID, true
		}
	}
	return 0, 0, false
}

// RingOneAddress returns a wg1 IP address
func RingOneAddress(zoneID, nodeID int) (netip.Addr, bool) {
	switch {
	case !ValidZoneID(zoneID) || !ValidNodeID(nodeID):
		return netip.Addr{}, false
	default:
		a4 := [4]uint8{10, 0, uint8(zoneID << 4), uint8(nodeID)}
		return netip.AddrFrom4(a4), true
	}
}