-- 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"

    -- Check if the key file exists
    if fileExists(keyFilePath) then
        print("Encryption key found.")
        local file = fs.open(keyFilePath, "r")
        local keyData = file.readAll()
        file.close()
        return keyData
    else
        -- Simulate downloading the key by creating a new one
        print("Downloading encryption key...")
        local clientId = "Doggy.net/client_v2.0"  -- You can customize this ID
        local key = "x3A7rB8zD2L5qW4nH1"  -- You can customize this key

        -- Save the ID and key to the XOR.key file
        local file = fs.open(keyFilePath, "w")
        file.write(clientId .. "," .. key) -- Store ID and key separated by a comma
        file.close()
        print("Encryption key downloaded and saved as XOR.key.")

        return clientId .. "," .. key
    end
end

-- Function to get client ID and key
local function getClientIdAndKey(encryptionKey)
    local clientId, key = encryptionKey:match("^(.*),(.*)$")
    return clientId, 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

    -- Open the first modem found
    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 (with decryption and protocol)
local function handleIncomingMessages(encryptionKey)
    local clientId, key = getClientIdAndKey(encryptionKey)

    while true do
        -- Receive message only with the custom protocol
        local senderId, encryptedMessage, protocol = rednet.receive(chatProtocol)

        -- Decrypt the incoming message
        local decryptedMessage = xorEncryptDecrypt(encryptedMessage, key)

        -- Split the username and chat message
        local username, chatMessage = decryptedMessage:match("^(.-): (.+)$")
        if username and chatMessage then
            displayMessage(username, chatMessage, false)
        else
            displayMessage(senderId, decryptedMessage, true) -- Handle messages from older clients
        end
    end
end

-- Function to send a message (with encryption and protocol)
local function sendMessage(username, encryptionKey)
    local clientId, key = getClientIdAndKey(encryptionKey)

    while true do
        print("Type your message (or 'exit' to quit): ")
        local userInput = read() -- Get the user's input
        if userInput == "exit" then
            print("Exiting chat...")
            shell.run("/disk/os/gui") -- Run the GUI program on exit
            break
        end

        -- Format the message to include the username
        local formattedMessage = username .. ": " .. userInput

        -- Encrypt the message before broadcasting
        local encryptedMessage = xorEncryptDecrypt(formattedMessage, key)

        -- Broadcast the encrypted message to all users with the custom protocol
        rednet.broadcast(encryptedMessage, chatProtocol)

        -- Display the unencrypted message locally
        displayMessage(username, userInput, false)
    end
end

-- Function to verify the encryption key
local function verifyEncryptionKey(encryptionKey)
    local clientId, key = getClientIdAndKey(encryptionKey)

    -- Check if the client ID matches the expected value (you can customize this)
    if clientId ~= "Client123" then
        rednet.broadcast("Error: Invalid client ID or encryption key! Generating a new key...", chatProtocol)

        -- Regenerate the encryption key
        local newEncryptionKey = downloadOrCreateKey()
        return newEncryptionKey, false -- Return the new key and verification status
    end

    return encryptionKey, true -- Return the original key and verification status
end

-- Main program
term.clear() -- Clear the terminal
term.setCursorPos(1, 1) -- Set cursor position

print("Welcome to the Doggy OS Network Chatroom!")

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

-- Ask the user to choose between public and private chatroom
print("Would you like to join a public chatroom or a private chatroom? (p for public, c for private)")
local chatroomChoice = read()

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

-- Download or load the encryption key from XOR.key
local encryptionKey = downloadOrCreateKey()

-- Verify the encryption key and regenerate if necessary
encryptionKey, isVerified = verifyEncryptionKey(encryptionKey)

-- Setup the modem
local modemSide = setupModem()
if modemSide == nil then return end -- Exit if no modem was found

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

-- Start monitoring messages and detecting jamming in parallel
parallel.waitForAny(function()
    handleIncomingMessages(encryptionKey)
end, function()
    sendMessage(username, encryptionKey)
end)