Lightweight Messaging System

local function update()
    local h = http.get "https://pastebin.com/raw/L0ZKLBRG"
    local f = fs.open(shell.getRunningProgram(), "w")
    f.write(h.readAll())
    f.close()
    h.close()
end

if ... == "update" then update() end

local m = peripheral.find "modem"
local s = peripheral.find "speaker"

local chan = 3636
print "Welcome to the Lightweight Messaging System (developed by GTech Potatronics)"

m.open(chan)

local username = settings.get "lms.username"
if username == nil then
    write "Username: "
    username = read()
end

local w, h = term.getSize()
local send_window = window.create(term.current(), 1, h, w, 1)
local message_window = window.create(term.current(), 1, 1, w, h - 1)

local function notification_sound()
    if s then
        for i = 4, 12, 4 do
            s.playNote("flute", 3, i)
            sleep(0.2)
        end
    end
end

local function exec_in_window(w, f)
    local x, y = term.getCursorPos()
    local last = term.redirect(w)
    f()
    term.redirect(last)
    w.redraw()
    term.setCursorPos(x, y)
end

local function print_message(txt)
    exec_in_window(message_window, function()
        print(txt)
    end)
end

local function trim(s)
   return s:match( "^%s*(.-)%s*$" )
end

local banned_text = {
    "yeet",
    "ecs dee",
    "dab",
}

if debug and debug.getmetatable then
    _G.getmetatable = debug.getmetatable
end

local function to_case_insensitive(text)
    return text:gsub("[a-zA-Z]", function(char) return ("[%s%s]"):format(char:lower(), char:upper()) end)
end

local function filter(text)
    local out = text
    for _, b in pairs(banned_text) do
        out = out:gsub(to_case_insensitive(b), "")
    end
    return out
end

local function strip_extraneous_spacing(text)
    return text:gsub("%s+", " ")
end

local function collapse_e_sequences(text)
    return text:gsub("ee+", "ee")
end

local function preproc(text)
    return trim(filter(strip_extraneous_spacing(collapse_e_sequences(text:sub(1, 128)))))
end

local function add_message(msg, usr)
    local msg, usr = preproc(msg), preproc(usr)
    if msg == "" or usr == "" then return end
    print_message(usr .. ": " .. msg)
end

local function send()
    term.redirect(send_window)
    term.setBackgroundColor(colors.white)
    term.setTextColor(colors.black)
    term.clear()
    local hist = {}
    while true do
        local msg = read(nil, hist)
        if msg == "!!exit" then return
        elseif msg == "!!update" then update() print_message "Updated. Please restart the program."
        else
            table.insert(hist, msg)
            if preproc(msg) == "" then
                print_message "Your message is considered spam."
            else
                add_message(msg, username)
                m.transmit(chan, chan, { message = msg, username = username })
            end
        end
    end
end

local function recv()
    while true do
        local _, _, channel, _, message = os.pullEvent "modem_message"
        if channel == chan and type(message) == "table" and message.message and message.username then
            notification_sound()
            add_message(message.message, message.username)
        end
    end
end

m.transmit(chan, chan, { username = username, message = "Connected." })
parallel.waitForAny(send, recv)