package shared

import "encoding/binary"

const PROTO_VERSION uint16 = 1

// pubKey - public key generated by the client
// privKey - private key generated by the client
// sessionKey - key established between two peers
// multicastKey - key shared between everyone for encrypting multicast pkts
// authSecret - secret given during registration for authenticating subsequent requests

const (
	_ uint16 = iota
	// (client -> server) requests a challenge to prove the ownership of the privKey
	// [ pubKey - 1216 bytes ]
	REQ_GET_CHALLENGE
	// (server -> client) provides a pubKey-encrypted authSecret
	// [ ciphertext - 1168 bytes ]
	RESP_GET_CHALLENGE
	// (client -> server) requests an IP
	// [ HMAC(authSecret, pubKey) - 32 bytes ] [ pubKey - 1216 bytes ]
	REQ_REGISTER
	// (server -> client) returns the assigned IP and pubKey-encrypted multicastKey
	// [ ip - 16 bytes ] [ ciphertext - 1168 bytes ]
	RESP_REGISTER
	// (client -> server -> client2) relays an encrypted packet to a specified peer
	// [ HMAC(authSecret, rest) - 32 bytes ] [ destIP - 16 bytes ] [ srcIP - 16 bytes ] [ encryptedPkt ]
	ENC_PKT
	// (client -> server -> *) broadcasts an encrypted packet
	// [ HMAC(authSecret, rest) - 32 bytes ] [ encryptedPkt ]
	BROADCAST_PKT
	// (client -> server) requests peer's pubKey from the server for encapsulation
	// [ ip - 16 bytes ]
	REQ_GET_PUBKEY
	// (server -> client) provides requested pubKey
	// [ ip - 16 bytes ] [ pubKey - 1216 bytes ]
	RESP_GET_PUBKEY
	// (client -> server -> client2) establishes a sessionKey with another peer
	// [ HMAC(authSecret, rest) - 32 bytes ] [ destIP - 16 bytes ] [ srcIP - 16 bytes ] [ ciphertext - 1120 bytes ]
	REQ_ESTABLISH
	// (client2 -> server -> client) acknowledges the sessionKey was established
	// [ HMAC(authSecret, rest) - 32 bytes ] [ destIP - 16 bytes ] [ srcIP - 16 bytes ]
	RESP_ESTABLISH
)

func BuildPkt(pktType uint16, parts ...[]byte) []byte {
	var total int
	for _, p := range parts {
		total += len(p)
	}

	out := make([]byte, 4, 4+total)
	binary.LittleEndian.PutUint16(out[0:], PROTO_VERSION)
	binary.LittleEndian.PutUint16(out[2:], pktType)

	for _, p := range parts {
		out = append(out, p...)
	}
	return out
}