// Copyright 2012 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.

package os

import "time"

// FindProcess looks for a running process by its pid.
//
// The Process it returns can be used to obtain information
// about the underlying operating system process.
//
// On Unix systems, FindProcess always succeeds and returns a Process
// for the given pid, regardless of whether the process exists.
func FindProcess(pid int) (*Process, error) {
	return findProcess(pid)
}

// 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) (*Process, error) {
	return startProcess(name, argv, attr)
}

// Release releases any resources associated with the Process p,
// rendering it unusable in the future.
// Release only needs to be called if Wait is not.
func (p *Process) Release() error {
	return p.release()
}

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

// Wait waits for the Process to exit, and then returns a
// ProcessState describing its status and an error, if any.
// Wait releases any resources associated with the Process.
// On most operating systems, the Process must be a child
// of the current process or an error will be returned.
func (p *Process) Wait() (*ProcessState, error) {
	return p.wait()
}

// Signal sends a signal to the Process.
// Sending Interrupt on Windows is not implemented.
func (p *Process) Signal(sig Signal) error {
	return p.signal(sig)
}

// UserTime returns the user CPU time of the exited process and its children.
func (p *ProcessState) UserTime() time.Duration {
	return p.userTime()
}

// SystemTime returns the system CPU time of the exited process and its children.
func (p *ProcessState) SystemTime() time.Duration {
	return p.systemTime()
}

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

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

// 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.sys()
}

// 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.
// (On Unix, *syscall.Rusage matches struct rusage as defined in the
// getrusage(2) manual page.)
func (p *ProcessState) SysUsage() interface{} {
	return p.sysUsage()
}

// Hostname returns the host name reported by the kernel.
func Hostname() (name string, err error) {
	return hostname()
}

// Readdir reads the contents of the directory associated with file and
// returns a slice of up to n FileInfo values, as would be returned
// by Lstat, in directory order. Subsequent calls on the same file will yield
// further FileInfos.
//
// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
// Readdir returns an empty slice, it will return a non-nil error
// explaining why. At the end of a directory, the error is io.EOF.
//
// If n <= 0, Readdir returns all the FileInfo from the directory in
// a single slice. In this case, if Readdir succeeds (reads all
// the way to the end of the directory), it returns the slice and a
// nil error. If it encounters an error before the end of the
// directory, Readdir returns the FileInfo read until that point
// and a non-nil error.
func (f *File) Readdir(n int) ([]FileInfo, error) {
	if f == nil {
		return nil, ErrInvalid
	}
	return f.readdir(n)
}

// Readdirnames reads and returns a slice of names from the directory f.
//
// If n > 0, Readdirnames returns at most n names. In this case, if
// Readdirnames returns an empty slice, it will return a non-nil error
// explaining why. At the end of a directory, the error is io.EOF.
//
// If n <= 0, Readdirnames returns all the names from the directory in
// a single slice. In this case, if Readdirnames succeeds (reads all
// the way to the end of the directory), it returns the slice and a
// nil error. If it encounters an error before the end of the
// directory, Readdirnames returns the names read until that point and
// a non-nil error.
func (f *File) Readdirnames(n int) (names []string, err error) {
	if f == nil {
		return nil, ErrInvalid
	}
	return f.readdirnames(n)
}