import com.google.cloud.NoCredentials;
import com.google.cloud.spanner.DatabaseClient;
import com.google.cloud.spanner.DatabaseId;
import com.google.cloud.spanner.Spanner;
import com.google.cloud.spanner.SpannerOptions;

import java.lang.reflect.Field;
import java.util.Map;

/**
 * Demonstrates that MultiplexedSessionDatabaseClient.CHANNEL_USAGE
 * leaks SpannerImpl instances on close().
 *
 * No emulator or credentials required — the leak occurs during
 * client construction, before any RPCs are made.
 */
public class SpannerChannelUsageLeak {
    public static void main(String[] args) throws Exception {
        Class<?> clazz = Class.forName(
            "com.google.cloud.spanner.MultiplexedSessionDatabaseClient");
        Field field = clazz.getDeclaredField("CHANNEL_USAGE");
        field.setAccessible(true);
        Map<?, ?> channelUsage = (Map<?, ?>) field.get(null);

        DatabaseId dbId = DatabaseId.of("test-project", "test-instance", "test-db");

        System.out.println("Creating and closing 100 Spanner clients...\n");

        for (int i = 1; i <= 100; i++) {
            Spanner spanner = SpannerOptions.newBuilder()
                .setProjectId("test-project")
                .setCredentials(NoCredentials.getInstance())
                .build()
                .getService();

            DatabaseClient client = spanner.getDatabaseClient(dbId);
            spanner.close();

            if (i % 10 == 0) {
                System.gc();
                long usedMb = (Runtime.getRuntime().totalMemory()
                    - Runtime.getRuntime().freeMemory()) / (1024 * 1024);
                System.out.printf(
                    "Iteration %3d: CHANNEL_USAGE size = %d, heap used = %d MB%n",
                    i, channelUsage.size(), usedMb);
            }
        }

        System.out.println("\nExpected CHANNEL_USAGE size after 100 create/close cycles: 0");
        System.out.println("Actual CHANNEL_USAGE size: " + channelUsage.size());
    }
}