local modem = peripheral.find("modem")
local PORT = 1

local function start()
    if modem then
        modem.open(PORT)
        modem.transmit(PORT, PORT, "User connected")
    end
    print("Chat program started.")
end

local function stop()
    if modem then
        modem.transmit(PORT, PORT, "User disconnected")
        modem.close(PORT)
    end
    print("Chat program stopped.")
end

local function restart()
    stop()
    start()
end

local function receiveLoop()
    while true do
        local event, side, channel, replyChannel, message, distance = os.pullEvent("modem_message")
        if channel == PORT then
            local x, y = term.getCursorPos()
            term.setCursorPos(1, y)
            term.clearLine()
            print("Received: " .. tostring(message))
            write("> ")
        end
    end
end

local function sendLoop()
    while true do
        write("> ")
        local input = read()
        if modem then
            modem.transmit(PORT, PORT, input)
        end
    end
end

local function main()
    if not modem then
        print("No modem attached")
        while true do os.pullEvent() end
    end
    
    parallel.waitForAny(receiveLoop, sendLoop)
end

return { start = start, stop = stop, restart = restart, main = main }