rednet

rednet.open("top")
term.clear()
term.setCursorPos(1,1)

local command = {"-quit", "-msg", "-users"}
local input = ""
local quit = false
CID = {0,1,2,3,4,5,6,7,8,9}
UID = {}
oldUID = {}
UID[os.computerID()+1] = CurrentUsername

function EraseLine()
  oldx, oldy = term.getCursorPos()
  term.clearLine()
  term.setCursorPos(1,oldy)
end

function GetUsers()
  for n=1,#UID do
    if n-1 ~= os.computerID() then
      rednet.send(n-1, "PING")
      idn, UID[n], distance = rednet.receive(0.5)
    end
  end
end

function Receive()
  GetUsers()
  local id, msg = rednet.receive()
  if msg == "PING" then
    rednet.send(id, CurrentUsername)
  elseif msg == "LOGIN" then
    GetUsers()
  elseif msg == "QUIT" then
    EraseLine()
    UID[id+1] = nil
  else
    EraseLine()
    print(msg)
  end
end

function Send()
  write(CurrentUsername.." > ")
  local iscommand = false
  local input = read()
  for i=1,#command do
    if input == command[i] then
      if i == 1 then
        iscommand = true
        rednet.broadcast("QUIT")
        rednet.broadcast("* * "..CurrentUsername.." has left RedNet.")
        term.clear()
        term.setCursorPos(1,1)
        rednet.close("top")
        quit = true
      elseif i == 2 then
        iscommand = true
        write("Send message to: ")
        local whisper = read()
        write("Message: ")
        local msg = read()
        rednet.send(tonumber(whisper), CurrentUsername.." whispers: "..msg, true)
      elseif i == 3 then
        iscommand = true
        for n=1, #UID do
          write(UID[n].." ")
        end
        write("\n")
      end
    end
  end
  if iscommand == false then
    rednet.broadcast("<"..CurrentUsername.."> "..input)
  end
end

print("-------------------------")
print("Welcome to RedNet, "..CurrentUsername.."!")
shell.run("realtime")
print("Current Realtime is "..Time)
print("Current Minecraft time is "..os.time())
GetUsers()
print("Current users online: ")
for key,value in pairs(UID) do
  write(value.." ")
end
write("\n")
print("-------------------------")
rednet.broadcast("LOGIN")
rednet.broadcast("* * "..CurrentUsername.." has joined RedNet.")

while quit == false do
  parallel.waitForAny(Receive, Send)
end