sos serv main

-- Stationary Computer: receiver.lua
-- By Gemini

-- CONFIGURATION --
local logFile = "gps_log.txt" -- The name of the file to save coordinates to.
local maxEntries = 10         -- The maximum number of coordinate entries to keep.

-- -- -- -- -- -- --

-- This table will hold the list of the last known coordinates.
local coordHistory = {}

-- Open the ender modem to receive messages.
-- Replace "top" with the side your modem is on.
rednet.open("top")

print("GPS Receiver is running.")
print("Listening for incoming coordinates...")
print("Log file: " .. logFile)
print("Press CTRL+T to terminate.")

-- Main loop to listen for messages.
while true do
    -- Wait for a message with the protocol "gps_coords".
    local senderId, message, protocol = rednet.receive("gps_coords")

    if message then
        -- Deserialize the message from a string back into a Lua table.
        local coordinates = textutils.unserialize(message)

        if coordinates and coordinates.x then
            local coordString = string.format("X: %d, Y: %d, Z: %d", coordinates.x, coordinates.y, coordinates.z)
            print("Received from " .. senderId .. ": " .. coordString)

            -- Add the new coordinate string to the beginning of our history table.
            table.insert(coordHistory, 1, coordString)

            -- If the history has more than the max number of entries, remove the oldest one.
            if #coordHistory > maxEntries then
                table.remove(coordHistory)
            end

            -- Now, save the updated history to the file.
            local file = fs.open(logFile, "w")
            if file then
                for i, entry in ipairs(coordHistory) do
                    file.writeLine(entry)
                end
                file.close()
            else
                print("Error: Could not open " .. logFile .. " for writing.")
            end
        end
    end
end