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// Copyright 2011 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 linux

// Package terminal provides support functions for dealing with terminals, as
// commonly found on UNIX systems.
//
// Putting a terminal into raw mode is the most common requirement:
//
//      oldState, err := terminal.MakeRaw(0)
//      if err != nil {
//              panic(err)
//      }
//      defer terminal.Restore(0, oldState)
package terminal

import (
        "io"
        "syscall"
        "unsafe"
)

// State contains the state of a terminal.
type State struct {
        termios syscall.Termios
}

// IsTerminal returns true if the given file descriptor is a terminal.
func IsTerminal(fd int) bool {
        var termios syscall.Termios
        err := syscall.Tcgetattr(fd, &termios)
        return err == nil
}

// MakeRaw put the terminal connected to the given file descriptor into raw
// mode and returns the previous state of the terminal so that it can be
// restored.
func MakeRaw(fd int) (*State, error) {
        var oldState State
        if err := syscall.Tcgetattr(fd, &oldState.termios); err != nil {
                return nil, err
        }

        newState := oldState.termios
        newState.Iflag &^= syscall.ISTRIP | syscall.INLCR | syscall.ICRNL | syscall.IGNCR | syscall.IXON | syscall.IXOFF
        newState.Lflag &^= syscall.ECHO | syscall.ICANON | syscall.ISIG
        if err := syscall.Tcsetattr(fd, syscall.TCSANOW, &newState); err != nil {
                return nil, err
        }

        return &oldState, nil
}

// Restore restores the terminal connected to the given file descriptor to a
// previous state.
func Restore(fd int, state *State) error {
        err := syscall.Tcsetattr(fd, syscall.TCSANOW, &state.termios)
        return err
}

//extern ioctl
func ioctl(int, int, unsafe.Pointer) int

// GetSize returns the dimensions of the given terminal.
func GetSize(fd int) (width, height int, err error) {
        var dimensions [4]uint16

        if ioctl(fd, syscall.TIOCGWINSZ, unsafe.Pointer(&dimensions)) < 0 {
                return -1, -1, syscall.GetErrno()
        }
        return int(dimensions[1]), int(dimensions[0]), nil
}

// ReadPassword reads a line of input from a terminal without local echo.  This
// is commonly used for inputting passwords and other sensitive data. The slice
// returned does not include the \n.
func ReadPassword(fd int) ([]byte, error) {
        var oldState syscall.Termios
        if err := syscall.Tcgetattr(fd, &oldState); err != nil {
                return nil, err
        }

        newState := oldState
        newState.Lflag &^= syscall.ECHO
        if err := syscall.Tcsetattr(fd, syscall.TCSANOW, &newState); err != nil {
                return nil, err
        }

        defer func() {
                syscall.Tcsetattr(fd, syscall.TCSANOW, &oldState)
        }()

        var buf [16]byte
        var ret []byte
        for {
                n, err := syscall.Read(fd, buf[:])
                if err != nil {
                        return nil, err
                }
                if n == 0 {
                        if len(ret) == 0 {
                                return nil, io.EOF
                        }
                        break
                }
                if buf[n-1] == '\n' {
                        n--
                }
                ret = append(ret, buf[:n]...)
                if n < len(buf) {
                        break
                }
        }

        return ret, nil
}