// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build darwin freebsd linux netbsd openbsd windows

package os

import (
	"syscall"
)

// StartProcess starts a new process with the program, arguments and attributes
// specified by name, argv and attr.
//
// StartProcess is a low-level interface. The os/exec package provides
// higher-level interfaces.
//
// If there is an error, it will be of type *PathError.
func StartProcess(name string, argv []string, attr *ProcAttr) (p *Process, err error) {
	// Double-check existence of the directory we want
	// to chdir into.  We can make the error clearer this way.
	if attr != nil && attr.Dir != "" {
		if _, err := Stat(attr.Dir); err != nil {
			pe := err.(*PathError)
			pe.Op = "chdir"
			return nil, pe
		}
	}

	sysattr := &syscall.ProcAttr{
		Dir: attr.Dir,
		Env: attr.Env,
		Sys: attr.Sys,
	}
	if sysattr.Env == nil {
		sysattr.Env = Environ()
	}
	for _, f := range attr.Files {
		sysattr.Files = append(sysattr.Files, f.Fd())
	}

	pid, h, e := syscall.StartProcess(name, argv, sysattr)
	if e != nil {
		return nil, &PathError{"fork/exec", name, e}
	}
	return newProcess(pid, h), nil
}

// Kill causes the Process to exit immediately.
func (p *Process) Kill() error {
	return p.Signal(Kill)
}

// ProcessState stores information about process as reported by Wait.
type ProcessState struct {
	pid    int                // The process's id.
	status syscall.WaitStatus // System-dependent status info.
	rusage *syscall.Rusage
}

// Pid returns the process id of the exited process.
func (p *ProcessState) Pid() int {
	return p.pid
}

// Exited returns whether the program has exited.
func (p *ProcessState) Exited() bool {
	return p.status.Exited()
}

// Success reports whether the program exited successfully,
// such as with exit status 0 on Unix.
func (p *ProcessState) Success() bool {
	return p.status.ExitStatus() == 0
}

// Sys returns system-dependent exit information about
// the process.  Convert it to the appropriate underlying
// type, such as syscall.WaitStatus on Unix, to access its contents.
func (p *ProcessState) Sys() interface{} {
	return p.status
}

// SysUsage returns system-dependent resource usage information about
// the exited process.  Convert it to the appropriate underlying
// type, such as *syscall.Rusage on Unix, to access its contents.
func (p *ProcessState) SysUsage() interface{} {
	return p.rusage
}

// Convert i to decimal string.
func itod(i int) string {
	if i == 0 {
		return "0"
	}

	u := uint64(i)
	if i < 0 {
		u = -u
	}

	// Assemble decimal in reverse order.
	var b [32]byte
	bp := len(b)
	for ; u > 0; u /= 10 {
		bp--
		b[bp] = byte(u%10) + '0'
	}

	if i < 0 {
		bp--
		b[bp] = '-'
	}

	return string(b[bp:])
}

func (p *ProcessState) String() string {
	if p == nil {
		return "<nil>"
	}
	status := p.Sys().(syscall.WaitStatus)
	res := ""
	switch {
	case status.Exited():
		res = "exit status " + itod(status.ExitStatus())
	case status.Signaled():
		res = "signal " + itod(int(status.Signal()))
	case status.Stopped():
		res = "stop signal " + itod(int(status.StopSignal()))
		if status.StopSignal() == syscall.SIGTRAP && status.TrapCause() != 0 {
			res += " (trap " + itod(status.TrapCause()) + ")"
		}
	case status.Continued():
		res = "continued"
	}
	if status.CoreDump() {
		res += " (core dumped)"
	}
	return res
}