if not arg[1] then

    error("File not found.",2)

end

local file = io.open(arg[1], "r")

local map = textutils.unserialise(file:read("*a"))

file:close()

rednet.open("back")

print("Welcome to snap.")

print("To add new intersection stand in the middle and type name or leave blank and press enter.")

print("After adding new intersection you can add connections by typing index numbers of intersections to connect to. To leave connection mode type -1.")

print("To save and quit type \":q\".")

print("If you wish to abort saving just terminate the program.")

while true do

    local name

    local conn

    local x, z

    write("Name: ")

    name = read()

    x, _, z = gps.locate(2)

    if name == ":q" or x == nil then

        break

    elseif name == "" then

        name = nil

    end

    map.intersections[#map.intersections+1] = {x = x, y = z, name = name}

    print("Index: "..#map.intersections)

    while true do

        write("Connection: ")

        conn = tonumber(read())

        if conn == -1 then

            break

        end

        map.connections[#map.connections+1] = {#map.intersections, conn}

    end

end

file = io.open(arg[1],"w")

file:write(textutils.serialise(map))

file:close()