package zones

import (
	"fmt"
	"io/fs"
	"net/netip"

	"git.jpi.io/amery/jpictl/pkg/wireguard"
)

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
	// RingsCount indicates how many wireguard rings we have
	RingsCount = 2
	// RingZeroPort is the port wireguard uses for ring0
	RingZeroPort = 51800
	// RingOnePort is the port wireguard uses for ring1
	RingOnePort = 51810
)

// RingInfo contains represents the Wireguard endpoint details
// for a Machine on a particular ring
type RingInfo struct {
	Ring    int               `toml:"ring"`
	Enabled bool              `toml:"enabled,omitempty"`
	Keys    wireguard.KeyPair `toml:"keys,omitempty"`
}

// Merge attempts to combine two RingInfo structs
func (ri *RingInfo) Merge(alter *RingInfo) error {
	switch {
	case alter == nil:
		return nil
	case ri.Ring != alter.Ring:
		// different ring
		return fmt.Errorf("invalid %s: %v ≠ %v", "ring", ri.Ring, alter.Ring)
	case ri.Enabled && !alter.Enabled:
		// can't disable via Merge
		return fmt.Errorf("invalid %s: %v → %v", "enabled", ri.Enabled, alter.Enabled)
	case !canMergeKeyPairs(ri.Keys, alter.Keys):
		// incompatible keypairs
		return fmt.Errorf("invalid %s: %s ≠ %s", "keys", ri.Keys, alter.Keys)
	}

	return ri.unsafeMerge(alter)
}

func (ri *RingInfo) unsafeMerge(alter *RingInfo) error {
	// enable via Merge
	if alter.Enabled {
		ri.Enabled = true
	}

	// fill the gaps on our keypair
	if ri.Keys.PrivateKey.IsZero() {
		ri.Keys.PrivateKey = alter.Keys.PrivateKey
	}
	if ri.Keys.PublicKey.IsZero() {
		ri.Keys.PublicKey = alter.Keys.PublicKey
	}

	return nil
}

func canMergeKeyPairs(p1, p2 wireguard.KeyPair) bool {
	switch {
	case !p1.PrivateKey.IsZero() && !p2.PrivateKey.IsZero() && !p1.PrivateKey.Equal(p2.PrivateKey):
		return false
	case !p1.PublicKey.IsZero() && !p2.PublicKey.IsZero() && !p1.PublicKey.Equal(p2.PublicKey):
		return false
	default:
		return true
	}
}

// RingAddressEncoder provides encoder/decoder access for a particular
// Wireguard ring
type RingAddressEncoder struct {
	ID     int
	Port   uint16
	Encode func(zoneID, nodeID int) (netip.Addr, bool)
	Decode func(addr netip.Addr) (zoneID, nodeID int, ok bool)
}

var (
	// RingZero is a wg0 address encoder/decoder
	RingZero = RingAddressEncoder{
		ID:     0,
		Port:   RingZeroPort,
		Decode: ParseRingZeroAddress,
		Encode: RingZeroAddress,
	}
	// RingOne is a wg1 address encoder/decoder
	RingOne = RingAddressEncoder{
		ID:     1,
		Port:   RingOnePort,
		Decode: ParseRingOneAddress,
		Encode: RingOneAddress,
	}
	// Rings provides indexed access to the ring address encoders
	Rings = [RingsCount]RingAddressEncoder{
		RingZero,
		RingOne,
	}
)

// 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, uint8(zoneID << 4), 0, uint8(nodeID)}
		return netip.AddrFrom4(a4), true
	}
}

var (
	_ MachineIterator = (*Ring)(nil)
	_ ZoneIterator    = (*Ring)(nil)
)

// A Ring describes all peers on a ring
type Ring struct {
	RingAddressEncoder
	ZoneIterator

	Peers []*RingPeer
}

// AddPeer adds a [Machine] to the ring
func (r *Ring) AddPeer(p *Machine) bool {
	ri, ok := p.getRingInfo(r.ID)
	if !ok {
		return false
	}

	nodeID := p.ID
	zoneID := p.Zone()
	addr, _ := r.Encode(zoneID, nodeID)

	rp := &RingPeer{
		Node:       p,
		Address:    addr,
		PrivateKey: ri.Keys.PrivateKey,
		PeerConfig: wireguard.PeerConfig{
			PublicKey: ri.Keys.PublicKey,
			Endpoint: wireguard.EndpointAddress{
				Host: p.FullName(),
				Port: r.Port,
			},
		},
	}

	switch {
	case r.ID == 0:
		r.setRingZeroAllowedIPs(rp)
	case p.IsGateway():
		r.setRingOneGatewayAllowedIPs(rp)
	default:
		r.setRingOneNodeAllowedIPs(rp)
	}

	r.Peers = append(r.Peers, rp)
	return true
}

func (r *Ring) setRingZeroAllowedIPs(rp *RingPeer) {
	zoneID, _, _ := r.Decode(rp.Address)

	// everyone on ring0 is a gateway to ring1
	addr, _ := RingOneAddress(zoneID, 0)
	rp.AllowCIDR(addr, 12)

	// peer
	rp.AllowCIDR(rp.Address, 32)
}

func (r *Ring) setRingOneGatewayAllowedIPs(rp *RingPeer) {
	zoneID, _, _ := r.Decode(rp.Address)

	// peer
	rp.AllowCIDR(rp.Address, 32)

	// ring1 gateways connect to all other ring1 networks
	r.ForEachZone(func(z *Zone) bool {
		if z.ID != zoneID {
			addr, _ := r.Encode(z.ID, 0)
			rp.AllowCIDR(addr, 12)
		}
		return false
	})

	// ring1 gateways also connect to all ring0 addresses
	r.ForEachZone(func(z *Zone) bool {
		z.ForEachMachine(func(p *Machine) bool {
			if p.IsGateway() {
				addr, _ := RingZeroAddress(z.ID, p.ID)
				rp.AllowCIDR(addr, 32)
			}
			return false
		})
		return false
	})
}

func (*Ring) setRingOneNodeAllowedIPs(rp *RingPeer) {
	// only to the peer itself
	rp.AllowCIDR(rp.Address, 32)
}

// ForEachMachine calls a function for each Machine in the ring
// until instructed to terminate the loop
func (r *Ring) ForEachMachine(fn func(*Machine) bool) {
	for _, pp := range r.Peers {
		if fn(pp.Node) {
			return
		}
	}
}

// ExportConfig builds a wgN.conf for the specified machine on the ring
func (r *Ring) ExportConfig(p *Machine) (*wireguard.Config, error) {
	var found bool

	out := &wireguard.Config{
		Interface: wireguard.InterfaceConfig{
			ListenPort: r.Port,
		},
	}

	for _, pp := range r.Peers {
		switch {
		case pp.Node == p:
			// current
			found = true
			out.Interface.Address = pp.Address
			out.Interface.PrivateKey = pp.PrivateKey
		default:
			// peer
			pc := pp.PeerConfig
			out.Peer = append(out.Peer, pc)
		}
	}

	if !found {
		return nil, fs.ErrNotExist
	}

	return out, nil
}

// A RingPeer is a node on a [Ring]
type RingPeer struct {
	Node *Machine

	Address    netip.Addr
	PrivateKey wireguard.PrivateKey
	PeerConfig wireguard.PeerConfig
}

// AllowCIDR allows an IP range via this peer
func (rp *RingPeer) AllowCIDR(addr netip.Addr, bits int) {
	cidr := netip.PrefixFrom(addr, bits)
	rp.PeerConfig.AllowedIPs = append(rp.PeerConfig.AllowedIPs, cidr)
}

// NewRing composes a new Ring for Wireguard setup
func NewRing(z ZoneIterator, m MachineIterator, ring int) (*Ring, error) {
	r := &Ring{
		RingAddressEncoder: Rings[ring],
		ZoneIterator:       z,
	}

	m.ForEachMachine(func(p *Machine) bool {
		r.AddPeer(p)
		return false
	})

	return r, nil
}