import java.io.*;
import javax.microedition.io.*;

/**
 * Batches status updates and sends them in one HTTP request to minimise
 * radio wake-ups on battery-constrained devices.
 */
public class BatchSender {
    private final Vector  pending  = new Vector();
    private final String  serverUrl;
    private final int     maxBatch;

    public BatchSender(String serverUrl, int maxBatch) {
        this.serverUrl = serverUrl;
        this.maxBatch  = maxBatch;
    }

    public synchronized void add(String ip, String status) {
        pending.addElement(ip + "=" + status);
        if (pending.size() >= maxBatch) flush();
    }

    public synchronized void flush() {
        if (pending.isEmpty()) return;
        StringBuffer body = new StringBuffer();
        for (int i = 0; i < pending.size(); i++) {
            if (i > 0) body.append('&');
            body.append(pending.elementAt(i));
        }
        pending.removeAllElements();
        sendHttp(body.toString());
    }

    private void sendHttp(String body) {
        HttpConnection conn = null;
        try {
            conn = (HttpConnection) Connector.open(serverUrl);
            conn.setRequestMethod(HttpConnection.POST);
            conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            OutputStream out = conn.openOutputStream();
            out.write(body.getBytes("UTF-8"));
            out.flush();
            out.close();
            conn.getResponseCode(); // wait for response
        } catch (Exception e) {
            // log; updates dropped — acceptable for status telemetry
        } finally {
            if (conn != null) try { conn.close(); } catch (Exception ignored) {}
        }
    }
}