App.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.time.Instant;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class App {

    static class PricePoint {
        String price;
        String timestamp;

        PricePoint(String price, String timestamp) {
            this.price = price;
            this.timestamp = timestamp;
        }

        @Override
        public String toString() {
            return "price=" + price + ", timestamp=" + timestamp;
        }
    }

    private static final Queue<PricePoint> priceQueue = new ConcurrentLinkedQueue<>();

    public static void main(String[] args) throws InterruptedException {
        String apiKey = System.getenv("TWELVE_DATA_API_KEY");

        if (apiKey == null || apiKey.isBlank()) {
            System.out.println("No API key found!");
            return;
        }

        ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();

        Runnable pollTask = () -> {
            try {
                String json = fetchJson(apiKey);
                String price = extractPrice(json);
                String timestamp = Instant.now().toString();

                PricePoint point = new PricePoint(price, timestamp);
                priceQueue.add(point);

                System.out.println("Added data point: " + point);
                System.out.println("Current queue size: " + priceQueue.size());
            } catch (Exception e) {
                System.out.println("Error fetching price: " + e.getMessage());
            }
        };

        // run immediately, then every 15 seconds
        scheduler.scheduleAtFixedRate(pollTask, 0, 15, TimeUnit.SECONDS);

        // let it run for 5 polls (75 seconds) then stop, so it doesn't run forever
        Thread.sleep(75000);
        scheduler.shutdown();
        System.out.println("Done. Total data points collected: " + priceQueue.size());
    }

    private static String fetchJson(String apiKey) throws Exception {
        String urlStr = "https://api.twelvedata.com/price?symbol=DIA&apikey=" + apiKey;
        URL url = new URL(urlStr);

        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");

        BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        StringBuilder response = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            response.append(line);
        }
        reader.close();
        conn.disconnect();

        return response.toString();
    }

    private static String extractPrice(String json) {
        String key = "\"price\"";
        int keyIndex = json.indexOf(key);
        int colonIndex = json.indexOf(':', keyIndex);
        int firstQuote = json.indexOf('"', colonIndex);
        int secondQuote = json.indexOf('"', firstQuote + 1);
        return json.substring(firstQuote + 1, secondQuote);
    }
}