package space.anyi.process;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.Optional;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 示例六：使用 ProcessHandle（JDK 9+）管理进程。
 *
 * 四个案例点各用一个 method 演示：
 * <ul>
 *   <li>handleFromProcess()     —— 从 Process 获取句柄，查询 pid / 元信息</li>
 *   <li>resolveByPid()          —— 通过 PID 解析句柄，处理不存在的 PID</li>
 *   <li>inspectProcessTree()    —— 遍历父子进程树，allProcesses() 统计</li>
 *   <li>terminateViaHandle()    —— 通过句柄 destroy，onExit() 等待退出</li>
 * </ul>
 * 子进程为 src/main/resources/code/processHandle/Main.java（打印 pid/args 后睡眠 30 秒）。
 */
public class ProcessHandleExample {
    private static final Logger log = LoggerFactory.getLogger(ProcessHandleExample.class);
    private static final File WORK_DIR = Paths.get(System.getProperty("user.dir"),
            "src", "main", "resources", "code", "processHandle").toFile();

    public static void main(String[] args) throws Exception {
        Jdk.compileFixture(WORK_DIR);
        handleFromProcess();
        resolveByPid();
        inspectProcessTree();
        terminateViaHandle();
    }

    /** 启动一个 processHandle 子进程程序（睡眠 30 秒，等待父进程检查/销毁） */
    private static Process startChild() throws IOException {
        return new ProcessBuilder(Jdk.java(), "-Dfile.encoding=UTF-8", "Main")
                .directory(WORK_DIR)
                .start();
    }

    /**
     * 案例点：从 Process 获取 ProcessHandle，查询 pid、元信息。
     * handle.pid() 应与 process.pid() 完全一致；
     * info() 返回 command / commandLine / startInstant / totalCpuDuration / user。
     */
    private static void handleFromProcess() throws Exception {
        log.info("== 从 Process 获取 ProcessHandle ==");
        Process process = startChild();
        Thread stdoutDrain = drain("stdout", process.getInputStream());
        Thread stderrDrain = drain("stderr", process.getErrorStream());
        // 稍等片刻，让 drain 线程先把子进程的启动横幅读走，再开始检查
        Thread.sleep(300);

        // 从 Process 取出进程句柄
        ProcessHandle handle = process.toHandle();

        // pid() 应与 process.pid() 一致
        log.info("process.pid()      = {}", process.pid());
        log.info("handle.pid()      = {}", handle.pid());
        log.info("pid 一致: {}", process.pid() == handle.pid());

        // isAlive —— 子进程此时正在睡眠，应为 true
        log.info("handle.isAlive()  = {}", handle.isAlive());

        // info() 返回进程元信息（均为 Optional，部分字段在进程退出后不再可读）
        ProcessHandle.Info info = handle.info();
        log.info("command()         = {}", info.command());
        log.info("commandLine()     = {}", info.commandLine());
        log.info("startInstant()    = {}", info.startInstant());
        log.info("totalCpuDuration()= {}", info.totalCpuDuration());
        log.info("user()            = {}", info.user());

        // supportsNormalTermination() —— Linux 返回 true，Windows 返回 false
        log.info("supportsNormalTermination() = {}", handle.supportsNormalTermination());

        // 销毁子进程，恢复环境
        handle.destroy();
        stdoutDrain.join();
        stderrDrain.join();
        process.waitFor();
        log.info("handleFromProcess 完成，退出码: {}", process.exitValue());
    }

    /**
     * 案例点：通过 PID 解析进程句柄。
     * ProcessHandle.of(pid) 返回 Optional，进程存在时有值，PID 不存在时为空。
     */
    private static void resolveByPid() throws Exception {
        log.info("== 通过 PID 解析 ProcessHandle ==");
        Process process = startChild();
        Thread stdoutDrain = drain("stdout", process.getInputStream());
        Thread stderrDrain = drain("stderr", process.getErrorStream());
        Thread.sleep(300);

        long pid = process.pid();
        log.info("子进程 PID: {}", pid);

        // 通过 PID 解析——应成功
        Optional<ProcessHandle> child = ProcessHandle.of(pid);
        log.info("ProcessHandle.of({}) 存在: {}", pid, child.isPresent());
        child.ifPresent(h -> {
            log.info("  pid     = {}", h.pid());
            log.info("  command = {}", h.info().command());
        });

        // 不存在的 PID——应返回空
        Optional<ProcessHandle> bogus = ProcessHandle.of(99999999L);
        log.info("ProcessHandle.of(99999999) 存在: {}", bogus.isPresent());

        // 恢复环境
        process.destroy();
        stdoutDrain.join();
        stderrDrain.join();
        process.waitFor();
        log.info("resolveByPid 完成，退出码: {}", process.exitValue());
    }

    /**
     * 案例点：遍历父子进程树。
     * current.children() 是当前 JVM 的直接子进程（应包含我们启动的子进程）；
     * child.parent() 应回溯到当前 JVM；
     * allProcesses() 统计当前用户可见的所有活跃进程。
     */
    private static void inspectProcessTree() throws Exception {
        log.info("== 进程树与 allProcesses ==");
        Process process = startChild();
        Thread stdoutDrain = drain("stdout", process.getInputStream());
        Thread stderrDrain = drain("stderr", process.getErrorStream());
        Thread.sleep(300);

        // 当前 JVM 进程句柄
        ProcessHandle current = ProcessHandle.current();
        log.info("当前 JVM pid: {}", current.pid());

        // 直接子进程——应包含我们刚启动的子进程
        log.info("当前 JVM 的直接子进程:");
        long[] childPids = current.children()
                .peek(h -> log.info("  子进程 pid: {}", h.pid()))
                .mapToLong(h -> h.pid())
                .toArray();
        log.info("子进程 PID {} 在 children() 中: {}", process.pid(),
                Arrays.binarySearch(childPids, process.pid()) >= 0);

        // 子进程的 parent——应指向当前 JVM
        ProcessHandle.of(process.pid()).ifPresent(child -> {
            Optional<ProcessHandle> parent = child.parent();
            log.info("子进程 parent 存在: {}", parent.isPresent());
            parent.ifPresent(p -> log.info("  parent pid = {}", p.pid()));
            log.info("  parent 就是当前 JVM: {}", parent.isPresent()
                    && parent.get().pid() == current.pid());
        });

        // descendants() 当前示例深度为 1，与 children() 内容一致
        log.info("descendants() 数量: {}", current.descendants().count());

        // allProcesses() 是静态方法，用接口名直接调用；统计当前用户可见的所有活跃进程
        try {
            long total = ProcessHandle.allProcesses().count();
            log.info("当前用户可见活跃进程总数: {}", total);
        } catch (Exception e) {
            // 部分平台/权限下可能受限
            log.info("allProcesses() 调用失败（权限受限）: {}", e.getMessage());
        }

        // 恢复环境
        process.destroy();
        stdoutDrain.join();
        stderrDrain.join();
        process.waitFor();
        log.info("inspectProcessTree 完成，退出码: {}", process.exitValue());
    }

    /**
     * 案例点：通过句柄销毁进程，对比 Process.destroy()。
     * handle.destroy() 发 SIGTERM（Linux）；
     * handle.onExit() 返回 CompletableFuture，join() 阻塞到进程真正退出；
     * 退出后通过 process.exitValue() 读取退出码。
     */
    private static void terminateViaHandle() throws Exception {
        log.info("== 通过句柄销毁进程 ==");
        Process process = startChild();
        Thread stdoutDrain = drain("stdout", process.getInputStream());
        Thread stderrDrain = drain("stderr", process.getErrorStream());
        Thread.sleep(300);
        ProcessHandle handle = process.toHandle();

        log.info("进程存活: {}", handle.isAlive());

        // 通过句柄发起终止（Linux 发 SIGTERM，Windows 走 TerminateProcess）
        boolean initiated = handle.destroy();
        log.info("destroy() 已发起: {}", initiated);

        // onExit() 阻塞到进程真正退出
        handle.onExit().join();
        log.info("进程已退出，handle.isAlive() = {}", handle.isAlive());

        // 回收输出流线程
        stdoutDrain.join();
        stderrDrain.join();

        // 读取退出码：被 SIGTERM 终止时通常为 143，Windows 为 1
        log.info("退出码 (process.exitValue()): {}", process.exitValue());
        log.info("terminateViaHandle 完成");
    }

    /** 起一个后台线程把给定输入流按行读取并打日志，读到 EOF（子进程退出）后结束 */
    private static Thread drain(String tag, InputStream in) {
        Thread thread = new Thread(() -> {
            try {
                new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8))
                        .lines()
                        .forEach(line -> log.info("[{}] {}", tag, line));
            } catch (java.io.UncheckedIOException e) {
                // 子进程被 destroy() 销毁时管道会立即关闭，读到一半抛 IOException 属预期行为
                log.info("[{}] 子进程被销毁，管道关闭（预期行为）", tag);
            }
        }, "drain-" + tag);
        thread.setDaemon(true);
        thread.start();
        return thread;
    }
}