messenger.lua

local function syncMessages()
    local width, height = term.getSize()
    while  true do
        local sender, message = rednet.receive()
        if sender then
            term.setCursorPos(1, height)
            print(message)
            term.write(string.rep("-", width))
            term.scroll(1)
        end
    end
end

local function mainLoop()
    local width, height = term.getSize()
    while true do
        term.setCursorPos(1, height)
        term.write(string.rep("-", width))
        term.scroll(1)

        term.setCursorPos(1, height)
        local message = io.read()
        term.setCursorPos(1, height-1)
        print(message)

        rednet.broadcast(message)
    end
end


term.clear()
local modem = peripheral.find("modem")

if modem then
    rednet.open("back")
    parallel.waitForAny(syncMessages, mainLoop)
else
    print("Modem not found, no service")
end