server

-- VARIABLES
local host_id = os.computerID()
local users = {}

-- FUNCTIONS
function user_joined(user_id)
  rednet.broadcast(user_id.." joined the server", "message")
  print(user_id.." joined the server")
  users[#users+1] = user_id
end

function user_left(user_id)
  local mess = user_id.." disconnected from the server"
  rednet.broadcast(mess, "message")
  print(user_id.." disconnected from the server")
  for i=1, #users do
    if users[i] == user_id then
      table.remove(users, i)
    end
  end
end

function id_request(user_id)
  rednet.send(user_id, host_id, "server_id_response")
  print(user_id.." requested server id")
end

function list_request(user_id)
  local mess = "Users on server: "
  for i=1, #users do
    mess = mess..users[i].." "
  end
  rednet.send(user_id, mess, "list_response")
  print(user_id.." requested user list")
end

function message_sent(user_id, message)
  rednet.broadcast(user_id.."- "..message, "message")
  print(user_id.."- "..message)
end
-- MAIN CODE
rednet.open("back")
rednet.broadcast("Server is online", "message")
print("Server is online")
while true do
  local event, param1, param2, param3 = os.pullEvent()
  if event == "rednet_message" then
    if param3 == "server_id" then
      id_request(param1)
    end
    if param3 == "join" then
      user_joined(param1)
    end
    if param3 == "leave" then
      user_left(param1)
    end
    if param3 == "list" then
      list_request(param1)
    end
    if param3 == "message" then
      message_sent(param1, param2)
    end
  end
  if event == "key" then
    write(">")
    local input = read()
    if input == "list" then
      if #users > 0 then
      local lista = "Users connected: "
      for i=1,#users do
        lista = lista..users[i].." "
      end
      print(lista)
      else
        print("There are no users")
      end
    elseif input == "exit" then
      rednet.broadcast("Server is offline", "message")
      textutils.slowPrint("Closing server . . .")
      break
    elseif input == "say" then
      write("Type your message: ")
      local messag = read()
      rednet.broadcast("server- "..messag, "message")
      print("server- "..messag)
    elseif input == "help" then
      print("list: shows user list")
      print("exit: closes server")
      print("say: allows you to say sth to chat")
    else
      print("Unknown command, type \"help\" for help")
    end
  end
end