-- 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.")
    else
        -- Simulate downloading the key by creating a new one
        print("Downloading encryption key...")
        local key = "defaultEncryptionKey123"  -- You can customize this key

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

    -- Read and return the key from the file
    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

    -- 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)
    term.setTextColor(colors.yellow) -- Set text color
    print("[" .. senderId .. "]: " .. message)
    term.setTextColor(colors.white) -- Reset text color
end

-- Function to handle incoming messages (with decryption and protocol)
local function handleIncomingMessages(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, encryptionKey)

        -- Display the decrypted message
        displayMessage(senderId, decryptedMessage)
    end
end

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

print("Doggy OS Network Chatroom Server!")

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

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

print("Server is running...")

-- Start handling incoming messages
handleIncomingMessages(encryptionKey)