-- Custom protocol (default)
local chatProtocol = "doggyChat"

-- Function to check if a file exists
local function fileExists(path)
    local file = fs.open(path, "r")
    if file then
        file.close()
        return true
    end
    return false
end

-- Function to download or create the XOR.key file
local function downloadOrCreateKey()
    local keyFilePath = "XOR.key"

    if fileExists(keyFilePath) then
        print("Encryption key found.")
    else
        print("Downloading encryption key...")
        local key = "x3A7rB8zD2L5qW4nH1"  -- Customize this key

        local file = fs.open(keyFilePath, "w")
        file.write(key)
        file.close()
        print("Encryption key downloaded and saved as XOR.key.")
    end

    local file = fs.open(keyFilePath, "r")
    local key = file.readAll()
    file.close()

    return key
end

-- XOR encryption function
local function xorEncryptDecrypt(message, key)
    local encrypted = {}
    for i = 1, #message do
        local char = string.byte(message, i)
        local keyChar = string.byte(key, (i - 1) % #key + 1)
        table.insert(encrypted, string.char(bit.bxor(char, keyChar)))
    end
    return table.concat(encrypted)
end

-- Function to list all connected modems
local function listModems()
    local modems = {}
    for _, side in ipairs(peripheral.getNames()) do
        if peripheral.getType(side) == "modem" then
            table.insert(modems, side)
        end
    end
    return modems
end

-- Function to setup the modem
local function setupModem()
    local modems = listModems()
    if #modems == 0 then
        print("No modems found! Please connect a modem and restart.")
        return nil
    end

    print("Connected modems:")
    for i, side in ipairs(modems) do
        print(i .. ": " .. side)
    end

    rednet.open(modems[1])
    print("Using modem on " .. modems[1])
    return modems[1]
end

-- Function to display a message in the chat
local function displayMessage(senderId, message, isOlderClient)
    term.setTextColor(colors.yellow) -- Set text color
    if isOlderClient then
        print("[Unknown User (" .. senderId .. ")]: " .. message) -- Show ID for older clients
    else
        print("[" .. senderId .. "]: " .. message)
    end
    term.setTextColor(colors.white) -- Reset text color
end

-- Function to handle incoming messages
local function handleIncomingMessages(encryptionKey)
    while true do
        local senderId, encryptedMessage, protocol = rednet.receive(chatProtocol)
        local decryptedMessage = xorEncryptDecrypt(encryptedMessage, encryptionKey)

        local username, chatMessage = decryptedMessage:match("^(.-): (.+)$")
        if username and chatMessage then
            displayMessage(username, chatMessage, false)
        else
            displayMessage(senderId, decryptedMessage, true)
        end
    end
end

-- Function to send a message
local function sendMessage(username, encryptionKey)
    while true do
        term.setCursorPos(1, 1)
        print("Type your message (or 'exit' to quit): ")
        local userInput = read()
        if userInput == "exit" then
            print("Exiting chat...")
            shell.run("/disk/os/gui")
            break
        end

        local formattedMessage = username .. ": " .. userInput
        local encryptedMessage = xorEncryptDecrypt(formattedMessage, encryptionKey)
        rednet.broadcast(encryptedMessage, chatProtocol)
        displayMessage(username, userInput, false)
    end
end

-- Function to create the chat GUI
local function createChatGUI()
    term.clear()
    term.setCursorPos(1, 1)
    print("======================================")
    print("     Welcome to Doggy OS Chatroom    ")
    print("======================================")

    -- Prompt for the username
    print("Enter your username:")
    local username = read()

    -- Ask the user to choose between public and private chatroom
    print("Join public (p) or private (c) chatroom?")
    local chatroomChoice = read():lower()

    if chatroomChoice == "p" then
        print("Joining public chatroom with protocol: " .. chatProtocol)
    else
        print("Enter a custom protocol name for the private chatroom:")
        chatProtocol = read()
        print("Using custom protocol: " .. chatProtocol)
    end

    return username
end

-- Main program
term.clear()
term.setCursorPos(1, 1)

local username = createChatGUI()

local encryptionKey = downloadOrCreateKey()
local modemSide = setupModem()
if modemSide == nil then return end

print("Type 'exit' to leave the chat.")

-- Start message handling
parallel.waitForAny(
    function() handleIncomingMessages(encryptionKey) end,
    function() sendMessage(username, encryptionKey) end
)