package inbound

import (
	"crypto/rand"
	"errors"
	"git.openprivacy.ca/openprivacy/libricochet-go/channels"
	"git.openprivacy.ca/openprivacy/libricochet-go/identity"
	"git.openprivacy.ca/openprivacy/libricochet-go/log"
	"git.openprivacy.ca/openprivacy/libricochet-go/utils"
	"git.openprivacy.ca/openprivacy/libricochet-go/wire/auth/3edh"
	"git.openprivacy.ca/openprivacy/libricochet-go/wire/control"
	"github.com/golang/protobuf/proto"
	"golang.org/x/crypto/ed25519"
	"golang.org/x/crypto/nacl/secretbox"
	"golang.org/x/crypto/pbkdf2"
	"golang.org/x/crypto/sha3"
)

// Server3DHAuthChannel wraps implementation of im.ricochet.auth.hidden-service"
type Server3DHAuthChannel struct {
	// PrivateKey must be set for client-side authentication channels
	ServerIdentity identity.Identity

	// Callbacks
	ServerAuthValid   func(hostname string, publicKey ed25519.PublicKey) (allowed, known bool)
	ServerAuthInvalid func(err error)

	// Internal state
	clientPubKey, clientEphmeralPublicKey, serverEphemeralPublicKey ed25519.PublicKey
	serverEphemeralPrivateKey                                       ed25519.PrivateKey
	channel                                                         *channels.Channel
}

// Type returns the type string for this channel, e.g. "im.ricochet.chat".
func (ah *Server3DHAuthChannel) Type() string {
	return "im.ricochet.auth.3dh"
}

// Singleton Returns whether or not the given channel type is a singleton
func (ah *Server3DHAuthChannel) Singleton() bool {
	return true
}

// OnlyClientCanOpen ...
func (ah *Server3DHAuthChannel) OnlyClientCanOpen() bool {
	return true
}

// Bidirectional Returns whether or not the given channel allows anyone to send messages
func (ah *Server3DHAuthChannel) Bidirectional() bool {
	return false
}

// RequiresAuthentication Returns whether or not the given channel type requires authentication
func (ah *Server3DHAuthChannel) RequiresAuthentication() string {
	return "none"
}

// Closed is called when the channel is closed for any reason.
func (ah *Server3DHAuthChannel) Closed(err error) {

}

// OpenInbound is the first method called for an inbound channel request.
// Infof an error is returned, the channel is rejected. Infof a RawMessage is
// returned, it will be sent as the ChannelResult message.
// Remote -> [Open Authentication Channel] -> Local
func (ah *Server3DHAuthChannel) OpenInbound(channel *channels.Channel, oc *Protocol_Data_Control.OpenChannel) ([]byte, error) {
	ah.channel = channel
	clientPublicKey, _ := proto.GetExtension(oc, Protocol_Data_Auth_TripleEDH.E_ClientPublicKey)
	clientEphmeralPublicKey, _ := proto.GetExtension(oc, Protocol_Data_Auth_TripleEDH.E_ClientEphmeralPublicKey)
	clientPubKeyBytes := clientPublicKey.([]byte)
	ah.clientPubKey = ed25519.PublicKey(clientPubKeyBytes[:])

	clientEphmeralPublicKeyBytes := clientEphmeralPublicKey.([]byte)
	ah.clientEphmeralPublicKey = ed25519.PublicKey(clientEphmeralPublicKeyBytes[:])

	clientHostname := utils.GetTorV3Hostname(clientPubKeyBytes)
	log.Debugf("Received inbound auth 3DH request from %v", clientHostname)

	// Generate Ephemeral Keys
	pubkey, privkey, _ := ed25519.GenerateKey(rand.Reader)
	ah.serverEphemeralPublicKey = pubkey
	ah.serverEphemeralPrivateKey = privkey

	var serverPubKeyBytes, serverEphemeralPubKeyBytes [32]byte
	copy(serverPubKeyBytes[:], ah.ServerIdentity.PublicKeyBytes()[:])
	copy(serverEphemeralPubKeyBytes[:], ah.serverEphemeralPublicKey[:])

	messageBuilder := new(utils.MessageBuilder)
	channel.Pending = false
	return messageBuilder.Confirm3EDHAuthChannel(ah.channel.ID, serverPubKeyBytes, serverEphemeralPubKeyBytes), nil
}

// OpenOutbound is the first method called for an outbound channel request.
// Infof an error is returned, the channel is not opened. Infof a RawMessage is
// returned, it will be sent as the OpenChannel message.
// Local -> [Open Authentication Channel] -> Remote
func (ah *Server3DHAuthChannel) OpenOutbound(channel *channels.Channel) ([]byte, error) {
	return nil, errors.New("server is not allowed to open 3dh channels")
}

// OpenOutboundResult is called when a response is received for an
// outbound OpenChannel request. Infof `err` is non-nil, the channel was
// rejected and Closed will be called immediately afterwards. `raw`
// contains the raw protocol message including any extension data.
// Input: Remote -> [ChannelResult] -> {Client}
// Output: {Client} -> [Proof] -> Remote
func (ah *Server3DHAuthChannel) OpenOutboundResult(err error, crm *Protocol_Data_Control.ChannelResult) {
	//
}

// Packet is called for each raw packet received on this channel.
// Input: Client -> [Proof] -> Remote
// OR
// Input: Remote -> [Result] -> Client
func (ah *Server3DHAuthChannel) Packet(data []byte) {
	res := new(Protocol_Data_Auth_TripleEDH.Packet)
	err := proto.Unmarshal(data[:], res)

	if err != nil {
		ah.channel.CloseChannel()
		return
	}

	if res.GetProof() != nil && ah.channel.Direction == channels.Inbound {

		// Server Identity <-> Client Ephemeral
		secret1 := ah.ServerIdentity.EDH(ah.clientEphmeralPublicKey)

		// Server Ephemeral <-> Client Identity
		secret2 := utils.EDH(ah.serverEphemeralPrivateKey, ah.clientPubKey)

		// Ephemeral <-> Ephemeral
		secret3 := utils.EDH(ah.serverEphemeralPrivateKey, ah.clientEphmeralPublicKey)

		var secret [96]byte
		copy(secret[0:32], secret1[:])
		copy(secret[32:64], secret2[:])
		copy(secret[64:96], secret3[:])

		pkey := pbkdf2.Key(secret[:], secret[:], 4096, 32, sha3.New512)
		var key [32]byte
		copy(key[:], pkey[:])
		var decryptNonce [24]byte
		ciphertext := res.GetProof().GetProof()

		if len(ciphertext) > 24 {
			copy(decryptNonce[:], ciphertext[:24])
			decrypted, ok := secretbox.Open(nil, ciphertext[24:], &decryptNonce, &key)

			if ok && string(decrypted) == "Hello World" {
				allowed, known := ah.ServerAuthValid(utils.GetTorV3Hostname(ah.clientPubKey), ah.clientPubKey)
				ah.channel.DelegateAuthorization()
				ah.channel.DelegateEncryption(key)
				log.Debugf("3DH Session Decrypted OK. Authenticating Connection!")
				messageBuilder := new(utils.MessageBuilder)
				result := messageBuilder.AuthResult3DH(allowed, known)
				ah.channel.SendMessage(result)
				ah.channel.CloseChannel()

				return
			}
		}

		messageBuilder := new(utils.MessageBuilder)
		result := messageBuilder.AuthResult3DH(false, false)
		ah.channel.SendMessage(result)
	}

	// Any other combination of packets is completely invalid
	// Fail the Authorization right here.
	ah.channel.CloseChannel()
}