/*
 * Copyright 2020-2020 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example;

import java.io.*;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import com.google.cloud.functions.invoker.runner.Invoker;

import org.springframework.cloud.function.adapter.gcp.GcfJarLauncher;

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

/**
 * Test support class for running tests on the local Cloud Function server.
 *
 * @author Daniel Zou
 * @author Mike Eltsufin
 */
final public class LocalServerTestSupport {

	private static final ExecutorService EXECUTOR = Executors.newCachedThreadPool();

	private static final String SERVER_READY_STRING = "Started ServerConnector";

	private static AtomicInteger nextPort = new AtomicInteger(8080);

	private LocalServerTestSupport() {
	}

	public static ServerProcess startServer(Class<?> springApplicationMainClass)
			throws InterruptedException, IOException {

		// Get the Java class path.
		String myClassPath = System.getProperty("java.class.path");
		assertThat(myClassPath).isNotNull();

		// Setup the Java Process command line string
		List<String> command = Arrays.asList(getJavaCommand(), "-classpath", myClassPath, Invoker.class.getName());
		ProcessBuilder processBuilder = new ProcessBuilder().command(command).redirectErrorStream(true);

		// Set environment variables.
		Map<String, String> environment = new HashMap<>();
		environment.put("PORT", String.valueOf(nextPort.getAndIncrement()));
		environment.put("K_SERVICE", "test-function");
		environment.put("FUNCTION_SIGNATURE_TYPE", "http");
		environment.put("FUNCTION_TARGET", GcfJarLauncher.class.getCanonicalName());
		environment.put("MAIN_CLASS", springApplicationMainClass.getCanonicalName());
		processBuilder.environment().putAll(environment);

		// Start the process and monitor the output logs in a separate thread.
		// Once the SERVER_READY_STRING is found in the logs, we know we are ready.
		Process serverProcess = processBuilder.start();
		CountDownLatch ready = new CountDownLatch(1);

		EXECUTOR.submit(() -> monitorOutput(serverProcess.getInputStream(), ready));
		boolean serverReady = ready.await(5, TimeUnit.SECONDS);
		if (!serverReady) {
			serverProcess.destroy();
			throw new AssertionError("Server never became ready");
		}

		return new ServerProcess(serverProcess);
	}

	private static void monitorOutput(InputStream processOutput, CountDownLatch ready) {
		try (BufferedReader reader = new BufferedReader(new InputStreamReader(processOutput))) {
			String line;
			while ((line = reader.readLine()) != null) {
				if (line.contains(SERVER_READY_STRING)) {
					ready.countDown();
				}

				System.out.println(line);

				if (line.contains("WARNING")) {
					throw new AssertionError("Found warning in server output:\n" + line);
				}
			}
		}
		catch (IOException e) {
			throw new UncheckedIOException(e);
		}
	}

	/**
	 * Returns the path to the java executable.
	 */
	private static String getJavaCommand() {
		File javaHome = new File(System.getProperty("java.home"));
		assertThat(javaHome.exists()).isTrue();

		File javaBin = new File(javaHome, "bin");
		File javaCommand = new File(javaBin, "java");
		assertThat(javaCommand.exists()).isTrue();

		return javaCommand.toString();
	}

	static class ServerProcess implements AutoCloseable {

		private final Process process;

		ServerProcess(Process process) {
			this.process = process;
		}

		Process process() {
			return process;
		}

		@Override
		public void close() {
			process().destroy();
		}
	}
}