local protocol = "sync_protocol"
local clientPath = "/disk/users/"

-- Get sync mode from arguments
local args = {...}
local syncMode = args[1] or "full" -- Default to full sync if no argument provided

if syncMode ~= "upload" and syncMode ~= "download" and syncMode ~= "full" then
    print("Invalid mode! Use: 'upload', 'download', or leave empty for full sync.")
    return
end

-- Check if the DomainServiceEnabled directory exists
local domainServicePath = "/disk/config/domain/DomainServiceEnabled.cfg/"
if not fs.exists(domainServicePath) then
    print("Error: " .. domainServicePath .. " does not exist. Sync process will be ignored.")
    return
end

-- Read the server ID from .domaincontrollerID file
local function getServerID()
    local filePath = ".domaincontrollerID"
    if not fs.exists(filePath) then
        print("Error: .domaincontrollerID file not found.")
        return nil
    end
    local file = fs.open(filePath, "r")
    local serverID = tonumber(file.readAll())
    file.close()
    return serverID
end

local serverID = getServerID()
if not serverID then
    print("Invalid server ID.")
    return
end

-- Open the modem
rednet.open(peripheral.getName(peripheral.find("modem") or error("No modem found")))

-- Function to compute file hashes
local function getFileHash(filePath)
    if not fs.exists(filePath) then return nil end
    local f = fs.open(filePath, "r")
    local content = f.readAll()
    f.close()
    return textutils.serialize(content)
end

-- Get file list with hashes
local function getFileList(path)
    local files = {}
    local function scan(dir)
        for _, file in pairs(fs.list(dir)) do
            local fullPath = dir .. file
            if fs.isDir(fullPath) then
                scan(fullPath .. "/")
            else
                files[fullPath:sub(#clientPath + 1)] = getFileHash(fullPath)
            end
        end
    end
    scan(path)
    return files
end

-- Delete files that no longer exist on the server
local function deleteMissingFiles(missingFiles)
    for _, file in pairs(missingFiles) do
        local filePath = clientPath .. file
        if fs.exists(filePath) then
            fs.delete(filePath)
            print("Deleted missing file:", file)
        end
    end
end

-- Perform sync
local function syncFiles()
    print("Connecting to server " .. serverID .. "...")

    -- Send file list with hashes to server
    rednet.send(serverID, { action = "sync_request", mode = syncMode, files = getFileList(clientPath) }, protocol)

    local id, response = rednet.receive(protocol, 5)
    if id == serverID and response.action == "sync_response" then
        if syncMode == "download" or syncMode == "full" then
            -- Download missing/updated files from server
            print("Downloading files from server...")
            for file, content in pairs(response.files_to_client) do
                local filePath = clientPath .. file
                local f = fs.open(filePath, "w")
                f.write(content)
                f.close()
                print("Updated from server:", file)
            end
        end

        if syncMode == "upload" or syncMode == "full" then
            -- Send missing/updated files to server
            rednet.send(serverID, { action = "sync_upload", files_to_server = {} }, protocol)
            local id2, clientResponse = rednet.receive(protocol, 5)
            if id2 == serverID and clientResponse.action == "sync_upload_request" then
                for _, file in pairs(clientResponse.files_needed) do
                    local filePath = clientPath .. file
                    if fs.exists(filePath) then
                        local f = fs.open(filePath, "r")
                        local content = f.readAll()
                        f.close()
                        clientResponse.files_to_server[file] = content
                    end
                end
                rednet.send(serverID, clientResponse, protocol)
            end
        end

        -- If files were deleted on the client side (missing from server), delete them locally
        if response.files_to_delete then
            deleteMissingFiles(response.files_to_delete)
        end
    else
        print("No response from server.")
    end
end

syncFiles()
print("Sync complete.")