package main

import (
	"errors"
	"fmt"
	"os"
	"os/exec"
	"os/signal"
	"syscall"
)

func main() {
	if len(os.Args) <= 1 {
		exitErr("Usage: parent <command> [<args>...]")
	}

	c := make(chan os.Signal, 1)
	signal.Notify(c)

	cmd := exec.Command(os.Args[1], os.Args[2:]...)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Env = os.Environ()

	if err := cmd.Start(); err != nil {
		exitErr(err)
	}

	go func() {
		for sig := range c {
			cmd.Process.Signal(sig)
		}
	}()

	if err := cmd.Wait(); err != nil {
		var e *exec.ExitError
		if errors.As(err, &e) {
			if e.ProcessState.Exited() {
				os.Exit(e.ProcessState.ExitCode())
			} else {
				status, ok := e.ProcessState.Sys().(syscall.WaitStatus)
				if ok && status.Signaled() {
					os.Exit(128 + int(status.Signal()))
				}
			}
		}
		exitErr(err)
	}
}

func exitErr(errs ...interface{}) {
	fmt.Fprintln(os.Stderr, errs...)
	os.Exit(1)
}