// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

//go:build !windows && !plan9

package container

import (
	"errors"
	"os"
	"syscall"
)

// processKiller terminates a step process together with its whole process
// group, which is the Unix counterpart of the Windows Job Object tree-kill.
//
// Background: a step often launches a process tree (a shell that starts a child
// which in turn spawns further background processes). The default
// exec.CommandContext cancellation only kills the direct child, so cancelling a
// job left the rest of the tree running. Because those orphans inherited the
// step's stdout/stderr pipe, cmd.Wait() also blocked forever and the runner
// hung.
//
// Steps are started with Setpgid (or Setsid for the PTY path, see
// getSysProcAttr), which makes the step process the leader of a new process
// group whose ID equals its PID. Signalling the negative PID delivers to every
// process still in that group, so we can tear down the whole tree atomically on
// cancellation, which also closes the inherited pipe handles so cmd.Wait() can
// return.
type processKiller struct {
	pgid int
}

// newProcessKiller captures the process group of p (an already-started
// process). Because the step is launched with Setpgid/Setsid, p is a group
// leader and its PGID equals its PID; children spawned afterwards stay in the
// same group unless they explicitly create their own.
func newProcessKiller(p *os.Process) (*processKiller, error) {
	return &processKiller{pgid: p.Pid}, nil
}

// Kill sends SIGKILL to the entire process group (the step process and every
// descendant that stayed in the group). A missing group (ESRCH) means the
// processes already exited and is not treated as an error.
func (k *processKiller) Kill() error {
	if k == nil || k.pgid <= 0 {
		return nil
	}
	if err := syscall.Kill(-k.pgid, syscall.SIGKILL); err != nil && !errors.Is(err, syscall.ESRCH) {
		return err
	}
	return nil
}

// Close is a no-op on Unix; there is no job handle to release.
func (k *processKiller) Close() error { return nil }