-- Function to check if DNS is locked by the existence of the lock file
local function isLocked()
    return fs.exists("/DNS/locked.cfg")
end

-- Function to get the correct password from a file (stored on DNS side)
local function getPassword()
    if not fs.exists("/DNS/password.txt") then
        return nil  -- If no password is set, return nil
    end
    local file = fs.open("/DNS/password.txt", "r")
    local password = file.readAll()
    file.close()
    return password
end

-- Function to load URL mappings from file
local function loadMappings()
    local mappings = {}
    if fs.exists("/DNS/URLS/") then
        for _, file in ipairs(fs.list("/DNS/URLS/")) do
            local f = fs.open("/DNS/URLS/" .. file, "r")
            local ip = f.readAll()
            f.close()
            mappings[file] = ip
        end
    end
    return mappings
end

-- Function to handle incoming requests
local function handleRequest(senderID, message)
    local url = message.url
    local password = message.password

    -- Check if DNS is locked and a password is required
    if isLocked() then
        local correctPassword = getPassword()
        if password ~= correctPassword then
            rednet.send(senderID, "ACCESS_DENIED")
            return
        end
    end

    local mappings = loadMappings()
    if mappings[url] then
        rednet.send(senderID, mappings[url])
    else
        rednet.send(senderID, "404_NOT_FOUND")
    end
end

-- Function to add a new URL mapping
local function addMapping(url, ip)
    local filePath = "/DNS/URLS/" .. url
    local file = fs.open(filePath, "w")
    file.write(ip)
    file.close()
end

-- Function to delete a URL mapping
local function deleteMapping(url)
    local filePath = "/DNS/URLS/" .. url
    if fs.exists(filePath) then
        fs.delete(filePath)
    else
        print("URL mapping does not exist.")
    end
end

-- UI for managing mappings (add/delete)
local function manageMappingsUI()
    while true do
        term.clear()
        print("Manage URL Mappings:")
        print("1. Add a new mapping")
        print("2. Delete an existing mapping")
        print("3. Exit")
        local choice = tonumber(read())

        if choice == 1 then
            print("Enter URL:")
            local url = read()
            print("Enter IP address:")
            local ip = read()
            addMapping(url, ip)
            print("Mapping added successfully!")
            sleep(2)
        elseif choice == 2 then
            print("Enter URL to delete:")
            local url = read()
            deleteMapping(url)
            print("Mapping deleted successfully!")
            sleep(2)
        elseif choice == 3 then
            break
        else
            print("Invalid option. Try again.")
            sleep(2)
        end
    end
end

-- Main loop to listen for DNS requests
local function runDNS()
    -- Automatically find and open the first available modem
    local sides = {"top", "bottom", "left", "right", "front", "back"}
    for _, side in ipairs(sides) do
        if peripheral.isPresent(side) and peripheral.getType(side) == "modem" then
            rednet.open(side)
            print("Modem opened on side " .. side)
            break
        end
    end

    print("DNS server is running... Press F1 for management.")

    while true do
        local event = os.pullEvent()

        -- Check if F1 is pressed to open the management UI
        if event == "key" and keys.getName(os.pullEvent("key")) == "f1" then
            manageMappingsUI()
        elseif event == "rednet_message" then
            local senderID, message = rednet.receive()

            -- Check if the message is a table (should contain `url` and `password`)
            if type(message) == "table" and message.url and message.password then
                handleRequest(senderID, message)
            else
                print("Invalid message received from ID " .. senderID)
                rednet.send(senderID, "INVALID_REQUEST")
            end
        end
    end
end

-- Run the DNS server
runDNS()