package com.ankurm.ssews;

import java.time.Instant;
import java.util.ArrayList;
import java.util.List;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.apache.tomcat.util.threads.ThreadPoolExecutor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.web.server.LocalServerPort;
import org.springframework.boot.tomcat.TomcatWebServer;
import org.springframework.boot.web.server.context.WebServerApplicationContext;

import static org.assertj.core.api.Assertions.assertThat;

/**
 * Forty open SSE streams on a ten-thread Tomcat.
 *
 * <p>This is the test that answers the objection people raise first &mdash; "doesn't SSE pin a
 * thread per client?" It does not. {@code SseEmitter} puts the request into asynchronous mode,
 * the request thread returns to the pool, and the response stays open with no thread attached to
 * it. Forty concurrent streams on a pool of ten is the cheapest way to show that; the same test
 * with a blocking handler deadlocks at the eleventh client.
 *
 * <p>What SSE does cost is a <em>socket</em> per stream, plus one serialise-and-write per stream
 * per broadcast, both of which the transcript makes visible.
 */
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT,
        properties = {"dashboard.broadcast.enabled=false", "server.tomcat.threads.max=10"})
class SseConcurrencyTest {

    private static final int CLIENTS = 40;

    @LocalServerPort
    int port;

    @Autowired
    EmitterRegistry registry;

    @Autowired
    WebServerApplicationContext context;

    @Test
    void fortyStreamsOnTenThreads() throws Exception {
        List<SseClient> clients = new ArrayList<>();
        try {
            for (int i = 0; i < CLIENTS; i++) {
                clients.add(new SseClient(port, "/sse/metrics"));
            }
            for (int i = 0; i < 200 && registry.open() < CLIENTS; i++) {
                Thread.sleep(25);
            }

            // Read the pool size off THIS context's own connector. Counting threads by name
            // does not work here: other @SpringBootTest contexts in the same JVM have their own
            // http-nio pools, and with a random port Tomcat names its threads http-nio-auto-N,
            // not http-nio-<actual port>. That mismatch made this assertion pass alone and fail
            // in the full suite.
            TomcatWebServer server = (TomcatWebServer) context.getWebServer();
            ThreadPoolExecutor pool = (ThreadPoolExecutor) server.getTomcat().getConnector()
                    .getProtocolHandler().getExecutor();

            System.out.println("=== server.tomcat.threads.max=10, clients=" + CLIENTS + " ===");
            System.out.println("emitters open        : " + registry.open());
            System.out.println("connector pool size  : " + pool.getPoolSize()
                    + " (max " + pool.getMaximumPoolSize() + ")");
            System.out.println("connector active     : " + pool.getActiveCount());

            assertThat(registry.open()).isEqualTo(CLIENTS);
            assertThat(pool.getMaximumPoolSize()).isEqualTo(10);
            assertThat(pool.getPoolSize()).isLessThanOrEqualTo(10);

            int delivered = registry.broadcast("metric",
                    new MetricSnapshot(1, "node-a", 0.5, 300, Instant.now()));
            System.out.println("one broadcast reached: " + delivered + " streams");
            assertThat(delivered).isEqualTo(CLIENTS);

            int received = 0;
            for (SseClient c : clients) {
                if (String.join("\n", c.read(12)).contains("event:metric")) {
                    received++;
                }
            }
            System.out.println("clients that read it : " + received);
            assertThat(received).isEqualTo(CLIENTS);
        }
        finally {
            for (SseClient c : clients) {
                try { c.close(); } catch (Exception ignored) { }
            }
        }
    }
}