<?php

namespace Amp\Process;

use Amp\ByteStream\ResourceInputStream;
use Amp\ByteStream\ResourceOutputStream;
use Amp\Deferred;
use Amp\Delayed;
use Amp\Loop;
use Amp\Promise;
use function Amp\call;

class Process {
    /** @var bool */
    private static $onWindows;

    /** @var resource|null */
    private $process;

    /** @var string */
    private $command;

    /** @var string */
    private $cwd = "";

    /** @var array */
    private $env = [];

    /** @var array */
    private $options;

    /** @var \Amp\ByteStream\ResourceOutputStream|null */
    private $stdin;

    /** @var \Amp\ByteStream\ResourceInputStream|null */
    private $stdout;

    /** @var \Amp\ByteStream\ResourceInputStream|null */
    private $stderr;

    /** @var int */
    private $pid = 0;

    /** @var int */
    private $oid = 0;

    /** @var \Amp\Deferred|null */
    private $deferred;

    /** @var string */
    private $watcher;

    /** @var bool */
    private $running = false;

    /**
     * @param   string|array $command Command to run.
     * @param   string|null $cwd Working directory or use an empty string to use the working directory of the current
     *     PHP process.
     * @param   mixed[] $env Environment variables or use an empty array to inherit from the current PHP process.
     * @param   mixed[] $options Options for proc_open().
     */
    public function __construct($command, string $cwd = null, array $env = [], array $options = []) {
        if (self::$onWindows === null) {
            self::$onWindows = \strncasecmp(\PHP_OS, "WIN", 3) === 0;
        }

        if (\is_array($command)) {
            $command = \implode(" ", \array_map("escapeshellarg", $command));
        }
        $this->command = $command;
        $this->cwd = $cwd ?? "";

        foreach ($env as $key => $value) {
            if (\is_array($value)) {
                throw new \Error("\$env cannot accept array values");
            }

            $this->env[(string) $key] = (string) $value;
        }

        $this->options = $options;
    }

    /**
     * Stops the process if it is still running.
     */
    public function __destruct() {
        if (\getmypid() === $this->oid) {
            $this->kill(); // Will only terminate if the process is still running.
        }

        if ($this->watcher !== null) {
            Loop::cancel($this->watcher);
        }

        if ($this->stdin) {
            $this->stdin->close();
        }

        if ($this->stdout) {
            $this->stdout->close();
        }

        if ($this->stderr) {
            $this->stderr->close();
        }

        if (\is_resource($this->process)) {
            \proc_close($this->process);
        }
    }

    /**
     * Resets process values.
     */
    public function __clone() {
        $this->process = null;
        $this->deferred = null;
        $this->watcher = null;
        $this->pid = 0;
        $this->oid = 0;
        $this->stdin = null;
        $this->stdout = null;
        $this->stderr = null;
        $this->running = false;
    }

    /**
     * @throws \Amp\Process\ProcessException If starting the process fails.
     * @throws \Amp\Process\StatusError If the process is already running.
     */
    public function start() {
        if ($this->deferred !== null) {
            throw new StatusError("The process has already been started");
        }

        $this->deferred = $deferred = new Deferred;

        $fd = [
            ["pipe", "r"], // stdin
            ["pipe", "w"], // stdout
            ["pipe", "w"], // stderr
            ["pipe", "w"], // exit code pipe
        ];

        if (self::$onWindows) {
            $command = $this->command;
        } else {
            $command = \sprintf(
                '{ (%s) <&3 3<&- 3>/dev/null & } 3<&0;' .
                'pid=$!; echo $pid >&3; wait $pid; RC=$?; echo $RC >&3; exit $RC',
                $this->command
            );
        }

        $this->process = @\proc_open($command, $fd, $pipes, $this->cwd ?: null, $this->env ?: null, $this->options);

        if (!\is_resource($this->process)) {
            $message = "Could not start process";
            if ($error = \error_get_last()) {
                $message .= \sprintf(" Errno: %d; %s", $error["type"], $error["message"]);
            }
            $deferred->fail(new ProcessException($message));
            return;
        }

        $this->oid = \getmypid();
        $status = \proc_get_status($this->process);

        if (!$status) {
            \proc_close($this->process);
            $this->process = null;
            $deferred->fail(new ProcessException("Could not get process status"));
            return;
        }

        if (self::$onWindows) {
            $this->pid = $status["pid"];
            $exitcode = $status["exitcode"];
        } else {
            // This blocking read will only block until the process scheduled, generally a few microseconds.
            $pid = \rtrim(@\fgets($pipes[3]));
            $exitcode = -1;

            if (!$pid || !\is_numeric($pid)) {
                $deferred->fail(new ProcessException("Could not determine PID"));
                return;
            }

            $this->pid = (int) $pid;
        }

        $this->stdin = new ResourceOutputStream($pipes[0]);
        $this->stdout = new ResourceInputStream($pipes[1]);
        $this->stderr = new ResourceInputStream($pipes[2]);
        \stream_set_blocking($pipes[3], false);

        $this->running = true;

        $process = &$this->process;
        $running = &$this->running;
        $this->watcher = Loop::onReadable($pipes[3], static function ($watcher, $resource) use (
            &$process, &$running, $exitcode, $deferred
        ) {
            Loop::cancel($watcher);
            $running = false;

            try {
                try {
                    if (self::$onWindows) {
                        // Avoid a generator on Unix
                        $code = call(function () use ($exitcode, $process) {
                            $status = \proc_get_status($process);

                            while ($status["running"]) {
                                yield new Delayed(10);
                                $status = \proc_get_status($process);
                            }

                            $code = $exitcode !== -1 ? $exitcode : $status["exitcode"];
                            return (int) $code;
                        });
                    } elseif (!\is_resource($resource) || \feof($resource)) {
                        throw new ProcessException("Process ended unexpectedly");
                    } else {
                        $code = (int) \rtrim(@\stream_get_contents($resource));
                    }
                } finally {
                    if (\is_resource($resource)) {
                        \fclose($resource);
                    }
                }
            } catch (\Throwable $exception) {
                $deferred->fail($exception);
                return;
            }

            $deferred->resolve($code);
        });

        Loop::unreference($this->watcher);
    }

    /**
     * @return \Amp\Promise<int> Succeeds with exit code of the process or fails if the process is killed.
     */
    public function join(): Promise {
        if ($this->deferred === null) {
            throw new StatusError("The process is not running");
        }

        if ($this->watcher !== null && $this->running) {
            Loop::reference($this->watcher);
        }

        return $this->deferred->promise();
    }

    /**
     * {@inheritdoc}
     */
    public function kill() {
        if ($this->running && \is_resource($this->process)) {
            $this->running = false;

            // Forcefully kill the process using SIGKILL.
            \proc_terminate($this->process, 9);

            Loop::cancel($this->watcher);

            $this->deferred->fail(new ProcessException("The process was killed"));
        }
    }

    /**
     * Sends the given signal to the process.
     *
     * @param int $signo Signal number to send to process.
     *
     * @throws \Amp\Process\StatusError If the process is not running.
     */
    public function signal(int $signo) {
        if (!$this->isRunning()) {
            throw new StatusError("The process is not running");
        }

        \proc_terminate($this->process, $signo);
    }

    /**
     * Returns the PID of the child process. Value is only meaningful if PHP was not compiled with --enable-sigchild.
     *
     * @return int
     *
     * @throws \Amp\Process\StatusError
     */
    public function getPid(): int {
        if ($this->pid === 0) {
            throw new StatusError("The process has not been started");
        }

        return $this->pid;
    }

    /**
     * Returns the command to execute.
     *
     * @return string The command to execute.
     */
    public function getCommand(): string {
        return $this->command;
    }

    /**
     * Gets the current working directory.
     *
     * @return string The current working directory an empty string if inherited from the current PHP process.
     */
    public function getWorkingDirectory(): string {
        if ($this->cwd === "") {
            return \getcwd() ?: "";
        }

        return $this->cwd;
    }

    /**
     * Gets the environment variables array.
     *
     * @return string[] Array of environment variables.
     */
    public function getEnv(): array {
        return $this->env;
    }

    /**
     * Gets the options to pass to proc_open().
     *
     * @return mixed[] Array of options.
     */
    public function getOptions(): array {
        return $this->options;
    }

    /**
     * Determines if the process is still running.
     *
     * @return bool
     */
    public function isRunning(): bool {
        return $this->running;
    }

    /**
     * Gets the process input stream (STDIN).
     *
     * @return \Amp\ByteStream\ResourceOutputStream
     *
     * @throws \Amp\Process\StatusError If the process is not running.
     */
    public function getStdin(): ResourceOutputStream {
        if ($this->stdin === null) {
            throw new StatusError("The process has not been started");
        }

        return $this->stdin;
    }

    /**
     * Gets the process output stream (STDOUT).
     *
     * @return \Amp\ByteStream\ResourceInputStream
     *
     * @throws \Amp\Process\StatusError If the process is not running.
     */
    public function getStdout(): ResourceInputStream {
        if ($this->stdout === null) {
            throw new StatusError("The process has not been started");
        }

        return $this->stdout;
    }

    /**
     * Gets the process error stream (STDERR).
     *
     * @return \Amp\ByteStream\ResourceInputStream
     *
     * @throws \Amp\Process\StatusError If the process is not running.
     */
    public function getStderr(): ResourceInputStream {
        if ($this->stderr === null) {
            throw new StatusError("The process has not been started");
        }

        return $this->stderr;
    }
}