from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.kdf.hkdf import HKDF
from cryptography.fernet import Fernet
import vendor.umsgpack as umsgpack
import base64
import time
import RNS

import traceback

class LinkCallbacks:
	def __init__(self):
		self.link_established = None
		self.link_closed = None
		self.packet = None
		self.resource_started = None
		self.resource_concluded = None

class Link:
	CURVE = ec.SECP256R1()
	ECPUBSIZE = 91
	BLOCKSIZE = 16

	PENDING   = 0x00
	HANDSHAKE = 0x01
	ACTIVE    = 0x02
	STALE     = 0x03
	CLOSED    = 0x04

	ACCEPT_NONE = 0x00
	ACCEPT_APP = 0x01
	ACCEPT_ALL = 0x02
	resource_strategies = [ACCEPT_NONE, ACCEPT_APP, ACCEPT_ALL]

	@staticmethod
	def validateRequest(owner, data, packet):
		if len(data) == (Link.ECPUBSIZE):
			try:
				link = Link(owner = owner, peer_pub_bytes = data[:Link.ECPUBSIZE])
				link.setLinkID(packet)
				RNS.log("Validating link request "+RNS.prettyhexrep(link.link_id), RNS.LOG_VERBOSE)
				link.handshake()
				link.attached_interface = packet.receiving_interface
				link.prove()
				link.request_time = time.time()
				RNS.Transport.registerLink(link)
				if link.owner.callbacks.link_established != None:
					link.owner.callbacks.link_established(link)
				RNS.log("Incoming link request "+str(link)+" accepted", RNS.LOG_VERBOSE)

			except Exception as e:
				RNS.log("Validating link request failed", RNS.LOG_VERBOSE)
				traceback.print_exc()
				return None

		else:
			RNS.log("Invalid link request payload size, dropping request", RNS.LOG_VERBOSE)
			return None


	def __init__(self, destination=None, owner=None, peer_pub_bytes = None):
		if destination != None and destination.type != RNS.Destination.SINGLE:
			raise TypeError("Links can only be established to the \"single\" destination type")
		self.rtt = None
		self.callbacks = LinkCallbacks()
		self.resource_strategy = Link.ACCEPT_NONE
		self.outgoing_resources = []
		self.incoming_resources = []
		self.status = Link.PENDING
		self.type = RNS.Destination.LINK
		self.owner = owner
		self.destination = destination
		self.attached_interface = None
		self.__encryption_disabled = False
		if self.destination == None:
			self.initiator = False
		else:
			self.initiator = True
		
		self.prv = ec.generate_private_key(Link.CURVE, default_backend())
		self.pub = self.prv.public_key()
		self.pub_bytes = self.pub.public_bytes(
			encoding=serialization.Encoding.DER,
			format=serialization.PublicFormat.SubjectPublicKeyInfo
		)

		if peer_pub_bytes == None:
			self.peer_pub = None
			self.peer_pub_bytes = None
		else:
			self.loadPeer(peer_pub_bytes)

		if (self.initiator):
			self.request_data = self.pub_bytes
			self.packet = RNS.Packet(destination, self.request_data, packet_type=RNS.Packet.LINKREQUEST)
			self.packet.pack()
			self.setLinkID(self.packet)
			RNS.Transport.registerLink(self)
			self.request_time = time.time()
			self.packet.send()
			RNS.log("Link request "+RNS.prettyhexrep(self.link_id)+" sent to "+str(self.destination), RNS.LOG_VERBOSE)


	def loadPeer(self, peer_pub_bytes):
		self.peer_pub_bytes = peer_pub_bytes
		self.peer_pub = serialization.load_der_public_key(peer_pub_bytes, backend=default_backend())
		self.peer_pub.curce = Link.CURVE

	def setLinkID(self, packet):
		self.link_id = RNS.Identity.truncatedHash(packet.raw)
		self.hash = self.link_id

	def handshake(self):
		self.status = Link.HANDSHAKE
		self.shared_key = self.prv.exchange(ec.ECDH(), self.peer_pub)
		self.derived_key = HKDF(
			algorithm=hashes.SHA256(),
			length=32,
			salt=self.getSalt(),
			info=self.getContext(),
			backend=default_backend()
		).derive(self.shared_key)

	def prove(self):
		signed_data = self.link_id+self.pub_bytes
		signature = self.owner.identity.sign(signed_data)

		proof_data = self.pub_bytes+signature
		proof = RNS.Packet(self, proof_data, packet_type=RNS.Packet.PROOF, context=RNS.Packet.LRPROOF)
		proof.send()

	def validateProof(self, packet):
		peer_pub_bytes = packet.data[:Link.ECPUBSIZE]
		signed_data = self.link_id+peer_pub_bytes
		signature = packet.data[Link.ECPUBSIZE:RNS.Identity.KEYSIZE/8+Link.ECPUBSIZE]

		if self.destination.identity.validate(signature, signed_data):
			self.loadPeer(peer_pub_bytes)
			self.handshake()
			self.rtt = time.time() - self.request_time
			self.attached_interface = packet.receiving_interface
			RNS.Transport.activateLink(self)
			RNS.log("Link "+str(self)+" established with "+str(self.destination)+", RTT is "+str(self.rtt), RNS.LOG_VERBOSE)
			rtt_data = umsgpack.packb(self.rtt)
			rtt_packet = RNS.Packet(self, rtt_data, context=RNS.Packet.LRRTT)
			rtt_packet.send()

			self.status = Link.ACTIVE
			if self.callbacks.link_established != None:
				self.callbacks.link_established(self)
		else:
			RNS.log("Invalid link proof signature received by "+str(self), RNS.LOG_VERBOSE)
			# TODO: should we really do this, or just wait
			# for a valid one? Needs analysis.
			self.teardown()


	def rtt_packet(self, packet):
		try:
			# TODO: This is crude, we should use the delta
			# to model a more representative per-bit round
			# trip time, and use that to set a sensible RTT
			# expectancy for the link. This will have to do
			# for now though.
			measured_rtt = time.time() - self.request_time
			plaintext = self.decrypt(packet.data)
			rtt = umsgpack.unpackb(plaintext)
			#RNS.log("Measured RTT is "+str(measured_rtt)+", received RTT is "+str(rtt))
			self.rtt = max(measured_rtt, rtt)
			self.status = Link.ACTIVE
		except Exception as e:
			self.teardown()

	def getSalt(self):
		return self.link_id

	def getContext(self):
		return None

	def teardown(self):
		if self.status != Link.PENDING:
			teardown_packet = RNS.Packet(self, self.link_id, context=RNS.Packet.LINKCLOSE)
			teardown_packet.send()
		self.status = Link.CLOSED
		self.link_closed()

	def teardown_packet(self, packet):
		try:
			plaintext = self.decrypt(packet.data)
			if plaintext == self.link_id:
				self.status = Link.CLOSED
				self.link_closed()
		except Exception as e:
			pass

	def link_closed(self):
		self.prv = None
		self.pub = None
		self.pub_bytes = None
		self.shared_key = None
		self.derived_key = None

		if self.callbacks.link_closed != None:
			self.callbacks.link_closed(self)


	def receive(self, packet):
		if not self.status == Link.CLOSED:
			if packet.receiving_interface != self.attached_interface:
				RNS.log("Link-associated packet received on unexpected interface! Someone might be trying to manipulate your communication!", RNS.LOG_ERROR)
			else:
				if packet.packet_type == RNS.Packet.DATA:
					if packet.context == RNS.Packet.NONE:
						plaintext = self.decrypt(packet.data)
						if (self.callbacks.packet != None):
							self.callbacks.packet(plaintext, packet)

					elif packet.context == RNS.Packet.LRRTT:
						if not self.initiator:
							self.rtt_packet(packet)

					elif packet.context == RNS.Packet.LINKCLOSE:
						self.teardown_packet(packet)

					elif packet.context == RNS.Packet.RESOURCE_ADV:
						packet.plaintext = self.decrypt(packet.data)
						if self.resource_strategy == Link.ACCEPT_NONE:
							pass
						elif self.resource_strategy == Link.ACCEPT_APP:
							if self.callbacks.resource != None:
								self.callbacks.resource(packet)
						elif self.resource_strategy == Link.ACCEPT_ALL:
							RNS.Resource.accept(packet, self.callbacks.resource_concluded)

					elif packet.context == RNS.Packet.RESOURCE_REQ:
						plaintext = self.decrypt(packet.data)
						if ord(plaintext[:1]) == RNS.Resource.HASHMAP_IS_EXHAUSTED:
							resource_hash = plaintext[1+RNS.Resource.MAPHASH_LEN:RNS.Identity.HASHLENGTH/8+1+RNS.Resource.MAPHASH_LEN]
						else:
							resource_hash = plaintext[1:RNS.Identity.HASHLENGTH/8+1]
						for resource in self.outgoing_resources:
							if resource.hash == resource_hash:
								resource.request(plaintext)

					elif packet.context == RNS.Packet.RESOURCE_HMU:
						plaintext = self.decrypt(packet.data)
						resource_hash = plaintext[:RNS.Identity.HASHLENGTH/8]
						for resource in self.incoming_resources:
							if resource_hash == resource.hash:
								resource.hashmap_update_packet(plaintext)

					elif packet.context == RNS.Packet.RESOURCE_ICL:
						plaintext = self.decrypt(packet.data)
						resource_hash = plaintext[:RNS.Identity.HASHLENGTH/8]
						for resource in self.incoming_resources:
							if resource_hash == resource.hash:
								resource.cancel()

					# TODO: find the most efficient way to allow multiple
					# transfers at the same time, sending resource hash on
					# each packet is a huge overhead. Probably some kind
					# of hash -> sequence map
					elif packet.context == RNS.Packet.RESOURCE:
						for resource in self.incoming_resources:
							resource.receive_part(packet)

				elif packet.packet_type == RNS.Packet.PROOF:
					if packet.context == RNS.Packet.RESOURCE_PRF:
						resource_hash = packet.data[0:RNS.Identity.HASHLENGTH/8]
						for resource in self.outgoing_resources:
							if resource_hash == resource.hash:
								resource.validateProof(packet.data)


	def encrypt(self, plaintext):
		if self.__encryption_disabled:
			return plaintext
		try:
			fernet = Fernet(base64.urlsafe_b64encode(self.derived_key))
			ciphertext = base64.urlsafe_b64decode(fernet.encrypt(plaintext))
			return ciphertext
		except Exception as e:
			RNS.log("Encryption on link "+str(self)+" failed. The contained exception was: "+str(e), RNS.LOG_ERROR)


	def decrypt(self, ciphertext):
		if self.__encryption_disabled:
			return ciphertext
		try:
			fernet = Fernet(base64.urlsafe_b64encode(self.derived_key))
			plaintext = fernet.decrypt(base64.urlsafe_b64encode(ciphertext))
			return plaintext
		except Exception as e:
			RNS.log("Decryption failed on link "+str(self)+". The contained exception was: "+str(e), RNS.LOG_ERROR)

	def link_established_callback(self, callback):
		self.callbacks.link_established = callback

	def link_closed_callback(self, callback):
		self.callbacks.link_closed = callback

	def packet_callback(self, callback):
		self.callbacks.packet = callback

	# Called when an incoming resource transfer is started
	def resource_started_callback(self, callback):
		self.callbacks.resource_started = callback

	# Called when a resource transfer is concluded
	def resource_concluded_callback(self, callback):
		self.callbacks.resource_concluded = callback

	def setResourceStrategy(self, resource_strategy):
		if not resource_strategy in Link.resource_strategies:
			raise TypeError("Unsupported resource strategy")
		else:
			self.resource_strategy = resource_strategy

	def register_outgoing_resource(self, resource):
		self.outgoing_resources.append(resource)

	def register_incoming_resource(self, resource):
		self.incoming_resources.append(resource)

	def cancel_outgoing_resource(self, resource):
		if resource in self.outgoing_resources:
			self.outgoing_resources.remove(resource)
		else:
			RNS.log("Attempt to cancel a non-existing incoming resource", RNS.LOG_ERROR)

	def cancel_incoming_resource(self, resource):
		if resource in self.incoming_resources:
			self.incoming_resources.remove(resource)
		else:
			RNS.log("Attempt to cancel a non-existing incoming resource", RNS.LOG_ERROR)

	def ready_for_new_resource(self):
		if len(self.outgoing_resources) > 0:
			return False
		else:
			return True

	def disableEncryption(self):
		if (RNS.Reticulum.should_allow_unencrypted()):
			RNS.log("The link "+str(self)+" was downgraded to an encryptionless link", RNS.LOG_NOTICE)
			self.__encryption_disabled = True
		else:
			RNS.log("Attempt to disable encryption on link, but encryptionless links are not allowed by config.", RNS.LOG_CRITICAL)
			RNS.log("Shutting down Reticulum now!", RNS.LOG_CRITICAL)
			RNS.panic()

	def encryption_disabled(self):
		return self.__encryption_disabled

	def __str__(self):
		return RNS.prettyhexrep(self.link_id)