-- module to access linux ARP cache

config = require "config"

_arpcache = {}
_ARPCACHE4 = '/sbin/ip -4 n'
_PING6     = '/bin/ping6 -c 1 -W 1'
_ARPCACHE6 = '/sbin/ip -6 n'

function _match_v4(ip)
  return string.match(ip,"%d*%.%d*%.%d*%.%d*")
end

_arpcache.cache = {}

function _arpcache.get_mac(ip)

  local rec = _arpcache.cache[ip]
  if rec and rec.timestamp+config.arp_ttl > os.time() then
    return rec["mac"]
  end

  local cmd
  if _match_v4(ip) then
    cmd = _ARPCACHE4
  else
    os.execute(_PING6..' '..ip)
    cmd = _ARPCACHE6
  end

  local f = io.popen(cmd)
  local res = nil
  local line, w
  
  while true do

    line = f:read()
    if not line then 
      break
    end

    w = {}

    for k in string.gmatch(line, "(%S+)") do
      table.insert(w, k)
    end

    if w[1]==ip then
      res = w[5]
      
      break
    end

  end 

  if res then
    _arpcache.cache[ip] = { mac = res, timestamp = os.time() }
  end

  f:close()
  return res 

end

return _arpcache