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/*******************************************************************************
*
* Copyright 2017 Stefan Majewsky <majewsky@gmx.net>
*
* This program is free software: you can redistribute it and/or modify it under
* the terms of the GNU General Public License as published by the Free Software
* Foundation, either version 3 of the License, or (at your option) any later
* version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
* A PARTICULAR PURPOSE. See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along with
* this program. If not, see <http://www.gnu.org/licenses/>.
*
*******************************************************************************/
package cli
import (
"fmt"
"io"
"os"
"regexp"
"strings"
terminal "golang.org/x/crypto/ssh/terminal"
)
//Choice is a thing that the user can choose during Query().
type Choice struct {
//If given, the choice can be selected by pressing the key that
//produces this character.
Shortcut byte
//The display string that describes this choice.
Text string
}
func (c Choice) hasShortcut() bool {
return c.Shortcut != '\000'
}
//Query displays a question and a set of answers and allows the user to select
//one of the answers. Returns the selected Choice instance, as well as its
//index in the original choices list (starting from 0).
func Query(prompt string, choices ...Choice) (Choice, int) {
if len(choices) == 0 {
return Choice{}, -1
}
//disable line wrap; unexpected wrapping would confuse our cursor-moving code
os.Stdout.Write([]byte("\x1B[?7l"))
defer os.Stdout.Write([]byte("\x1B[?7h"))
//display question
os.Stdout.Write([]byte(strings.TrimSuffix(prompt, "\n") + "\n"))
selected := 0
buf := buffer{Input: os.Stdin}
OUTER:
for {
displayChoices(os.Stdout, choices, selected)
input := buf.getNextInput()
if len(input) == 1 {
//single character entered - check if a shortcut matches
for idx, choice := range choices {
if choice.Shortcut == input[0] {
selected = idx
break OUTER
}
}
}
switch string(input) {
case "\r", "\n":
break OUTER
case "\x1B[A": // Up arrow key
selected--
if selected < 0 {
selected = 0
}
case "\x1B[B": // Down arrow key
selected++
if selected >= len(choices) {
selected = len(choices) - 1
}
case "\x03": // Ctrl-C
fmt.Fprintf(os.Stderr, "Interrupted!")
os.Exit(255)
default:
fmt.Printf("%#v\n", string(input))
}
//prepare to re-render choices
removeDisplayLines(len(choices))
}
//clear query display
removeDisplayLines(len(choices) + 1)
//display question + chosen answer
fmt.Fprintf(os.Stdout, "%s -> %s\n",
strings.TrimSuffix(prompt, "\n"),
strings.TrimSpace(choices[selected].Text),
)
return choices[selected], selected
}
func removeDisplayLines(n int) {
for idx := 0; idx < n; idx++ {
os.Stdout.Write([]byte("\x1B[A\x1B[2K"))
}
}
func displayChoices(out io.Writer, choices []Choice, selectedIndex int) {
hasShortcuts := false
for _, choice := range choices {
if choice.hasShortcut() {
hasShortcuts = true
break
}
}
for idx, choice := range choices {
text := " " + strings.TrimSpace(choice.Text) + " \n"
if hasShortcuts {
shortcut := choice.Shortcut
if !choice.hasShortcut() {
shortcut = ' '
}
text = fmt.Sprintf(" [%c]%s", shortcut, text)
}
if idx == selectedIndex {
out.Write(Styled(text, AnsiInverse).DisplayString(true))
} else {
out.Write([]byte(text))
}
}
}
var ansiEscapeRx = regexp.MustCompile(`^\x1B\[[\x20-\x3F]*[\x40-\x7E]`)
type buffer struct {
Input io.Reader
buf [128]byte
fill int
}
func (b *buffer) getNextInput() []byte {
//do we have a simple input character?
if b.fill > 0 && b.buf[0] != '\x1B' {
result := append([]byte(nil), b.buf[0])
copy(b.buf[0:], b.buf[1:])
b.fill--
return result
}
//do we have a full ANSI escape sequence?
match := ansiEscapeRx.Find(b.buf[0:b.fill])
if match != nil {
result := append([]byte(nil), match...)
copy(b.buf[0:], b.buf[len(match):])
b.fill -= len(match)
return result
}
oldState, err := terminal.MakeRaw(0)
if err != nil {
panic(err)
}
defer terminal.Restore(0, oldState)
//fill buffer some more
n, err := os.Stdin.Read(b.buf[b.fill:])
if err != nil {
panic(err)
}
b.fill += n
return b.getNextInput() //restart
}
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