/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *--------------------------------------------------------------------------------------------*/

package com.github.copilot.sdk;

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.Socket;
import java.util.concurrent.CompletableFuture;

import org.junit.jupiter.api.Test;

import com.github.copilot.sdk.events.AssistantMessageEvent;
import com.github.copilot.sdk.json.MessageOptions;

/**
 * Tests for timeout edge cases in {@link CopilotSession#sendAndWait}.
 * <p>
 * These tests prove two defects in the current per-call
 * {@code ScheduledExecutorService} approach:
 * <ol>
 * <li>A timeout fires after {@code close()}, leaking a {@code TimeoutException}
 * onto the returned future.</li>
 * <li>Each {@code sendAndWait} call spawns a new OS thread (~1 MB stack),
 * instead of reusing a shared scheduler thread.</li>
 * </ol>
 */
public class TimeoutEdgeCaseTest {

    /**
     * Creates a {@link JsonRpcClient} whose {@code invoke()} returns futures that
     * never complete. The reader thread blocks forever on the input stream, and
     * writes go to a no-op output stream.
     */
    private JsonRpcClient createHangingRpcClient() throws Exception {
        InputStream blockingInput = new InputStream() {
            @Override
            public int read() throws IOException {
                try {
                    Thread.sleep(Long.MAX_VALUE);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    return -1;
                }
                return -1;
            }
        };
        ByteArrayOutputStream sinkOutput = new ByteArrayOutputStream();

        var ctor = JsonRpcClient.class.getDeclaredConstructor(InputStream.class, java.io.OutputStream.class,
                Socket.class, Process.class);
        ctor.setAccessible(true);
        return (JsonRpcClient) ctor.newInstance(blockingInput, sinkOutput, null, null);
    }

    /**
     * After {@code close()}, the future returned by {@code sendAndWait} must NOT be
     * completed by a stale timeout.
     * <p>
     * Current buggy behavior: the per-call scheduler is not cancelled by
     * {@code close()}, so its 2-second timeout fires during the 5-second
     * {@code session.destroy} RPC wait, completing the future with
     * {@code TimeoutException}.
     * <p>
     * Expected behavior after fix: {@code close()} cancels pending timeouts before
     * the blocking RPC call, so the future remains incomplete.
     */
    @Test
    void testTimeoutDoesNotFireAfterSessionClose() throws Exception {
        JsonRpcClient rpc = createHangingRpcClient();
        try {
            CopilotSession session = new CopilotSession("test-timeout-id", rpc);

            CompletableFuture<AssistantMessageEvent> result = session
                    .sendAndWait(new MessageOptions().setPrompt("hello"), 2000);

            assertFalse(result.isDone(), "Future should be pending before timeout fires");

            // close() blocks up to 5s on session.destroy RPC. The 2s timeout
            // fires during that window with the current per-call scheduler.
            session.close();

            assertFalse(result.isDone(), "Future should not be completed by a timeout after session is closed. "
                    + "The per-call ScheduledExecutorService leaked a TimeoutException.");
        } finally {
            rpc.close();
        }
    }

    /**
     * A shared scheduler should reuse a single thread across multiple
     * {@code sendAndWait} calls, rather than spawning a new OS thread per call.
     * <p>
     * Current buggy behavior: two calls create two {@code sendAndWait-timeout}
     * threads.
     * <p>
     * Expected behavior after fix: two calls still use only one scheduler thread.
     */
    @Test
    void testSendAndWaitReusesTimeoutThread() throws Exception {
        JsonRpcClient rpc = createHangingRpcClient();
        try {
            CopilotSession session = new CopilotSession("test-thread-count-id", rpc);

            long baselineCount = countTimeoutThreads();

            CompletableFuture<AssistantMessageEvent> result1 = session
                    .sendAndWait(new MessageOptions().setPrompt("hello1"), 30000);

            Thread.sleep(100);
            long afterFirst = countTimeoutThreads();
            assertTrue(afterFirst >= baselineCount + 1,
                    "Expected at least one new sendAndWait-timeout thread after first call. " + "Baseline: "
                            + baselineCount + ", after: " + afterFirst);

            CompletableFuture<AssistantMessageEvent> result2 = session
                    .sendAndWait(new MessageOptions().setPrompt("hello2"), 30000);

            Thread.sleep(100);
            long afterSecond = countTimeoutThreads();
            assertTrue(afterSecond == afterFirst,
                    "Shared scheduler should reuse the same thread — no new threads after second call. "
                            + "After first: " + afterFirst + ", after second: " + afterSecond);

            result1.cancel(true);
            result2.cancel(true);
            session.close();
        } finally {
            rpc.close();
        }
    }

    /**
     * Counts the number of live threads whose name contains "sendAndWait-timeout".
     */
    private long countTimeoutThreads() {
        return Thread.getAllStackTraces().keySet().stream().filter(t -> t.getName().contains("sendAndWait-timeout"))
                .filter(Thread::isAlive).count();
    }
}