add "cli" package with a Query method

1 files changed, 186 insertions, 0 deletions

diff --git a/pkg/cli/query.go b/pkg/cli/query.go
new file mode 100644
index 0000000..a81d153
--- /dev/null
+++ b/pkg/cli/query.go
@@ -0,0 +1,186 @@
+/*******************************************************************************
+*
+* 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 during doQuery(); 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
+}