# nim-eth - Node Discovery Protocol v5
# Copyright (c) 2020-2021 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
#
## Session cache as mentioned at
## https://github.com/ethereum/devp2p/blob/master/discv5/discv5-theory.md#session-cache
##

{.push raises: [Defect].}

import
  std/options,
  stint, stew/endians2, stew/shims/net,
  node, lru

export lru

const
  aesKeySize* = 128 div 8
  keySize = sizeof(NodeId) +
            16 + # max size of ip address (ipv6)
            2 # Sizeof port

type
  AesKey* = array[aesKeySize, byte]
  SessionKey* = array[keySize, byte]
  SessionValue* = array[sizeof(AesKey) + sizeof(AesKey), byte]
  Sessions* = LRUCache[SessionKey, SessionValue]

func makeKey(id: NodeId, address: Address): SessionKey =
  var pos = 0
  result[pos ..< pos+sizeof(id)] = toBytes(id)
  pos.inc(sizeof(id))
  case address.ip.family
  of IpAddressFamily.IpV4:
    result[pos ..< pos+sizeof(address.ip.address_v4)] = address.ip.address_v4
  of IpAddressFamily.IpV6:
    result[pos ..< pos+sizeof(address.ip.address_v6)] = address.ip.address_v6
  pos.inc(sizeof(address.ip.address_v6))
  result[pos ..< pos+sizeof(address.port)] = toBytes(address.port.uint16)

func store*(s: var Sessions, id: NodeId, address: Address, r, w: AesKey) =
  var value: array[sizeof(r) + sizeof(w), byte]
  value[0 .. 15] = r
  value[16 .. ^1] = w
  s.put(makeKey(id, address), value)

func load*(s: var Sessions, id: NodeId, address: Address, r, w: var AesKey): bool =
  let res = s.get(makeKey(id, address))
  if res.isSome():
    let val = res.get()
    copyMem(addr r[0], unsafeAddr val[0], sizeof(r))
    copyMem(addr w[0], unsafeAddr val[sizeof(r)], sizeof(w))
    return true
  else:
    return false

func del*(s: var Sessions, id: NodeId, address: Address) =
  s.del(makeKey(id, address))