absprompt.go

package terminal

import (
	"bytes"
	"fmt"
	"io"
	"strings"
)

// AbsPrompt is a wrapper around a Reader which will write a prompt, wait for a
// user's input, and return it.  It will print whatever needs to be printed on
// demand to an io.Writer, using ANSI to ensure the cursor is always at the
// right screen location, allowing the AbsPrompt to be used concurrently with
// other screen writing.  AbsPrompt stores the Reader's prior state in order to
// avoid unnecessary writes.
type AbsPrompt struct {
	*Reader
	prompt      string
	Out         io.Writer
	buf         bytes.Buffer
	x, y        int
	promptWidth int
	line        string
	pos         int
	prompted    bool
}

// NewAbsPrompt returns an AbsPrompt which will read lines from r, write its
// prompt and current line to w, and use p as the prompt string.
func NewAbsPrompt(r io.Reader, w io.Writer, p string) *AbsPrompt {
	var prompt = &AbsPrompt{Reader: NewReader(r), Out: w, buf: bytes.Buffer{}, x: 1, y: 1}
	prompt.SetPrompt(p)
	return prompt
}

// ReadLine delegates to the reader's ReadLine function
func (p *AbsPrompt) ReadLine() (string, error) {
	line, err := p.Reader.ReadLine()
	return line, err
}

// SetPrompt changes the current prompt.  This shouldn't be called while a
// ReadLine is in progress.
func (p *AbsPrompt) SetPrompt(s string) {
	p.prompt = s
	p.promptWidth = VisualLength(p.prompt)
}

// SetLocation changes the internal x and y coordinates.  If this is called
// while a ReadLine is in progress, you won't be happy.
func (p *AbsPrompt) SetLocation(x, y int) {
	p.x = x + 1
	p.y = y + 1
}

// NeedWrite returns true if there are any pending changes to the line or
// cursor position
func (p *AbsPrompt) NeedWrite() bool {
	line, pos := p.LinePos()
	return line != p.line || pos != p.pos
}

// WriteAll forces a write of the entire prompt
func (p *AbsPrompt) WriteAll() {
	line, pos := p.LinePos()

	p.printAt(0, p.prompt+p.line)
	p.pos = len(p.line)

	if p.line != line {
		prevLine := p.line

		lpl := len(prevLine)
		ll := len(line)
		bigger := lpl - ll
		if bigger > 0 {
			fmt.Fprintf(p.Out, strings.Repeat(" ", bigger))
			p.pos += bigger
		}
	}

	if p.pos != pos {
		p.pos = pos
		p.PrintCursorMovement()
	}
}

// WriteChanges attempts to only write to the console when something has
// changed (line text or the cursor position).  It will also print the prompt
// if that hasn't yet been printed.
func (p *AbsPrompt) WriteChanges() {
	line, pos := p.LinePos()

	if !p.prompted {
		p.PrintPrompt()
		p.prompted = true
	}

	if p.line != line {
		prevLine := p.line
		p.line = line
		p.PrintLine()

		lpl := len(prevLine)
		ll := len(line)
		bigger := lpl - ll
		if bigger > 0 {
			fmt.Fprintf(p.Out, strings.Repeat(" ", bigger))
			p.pos += bigger
		}
	}

	if p.pos != pos {
		p.pos = pos
		p.PrintCursorMovement()
	}
}

// WriteChangesNoCursor prints prompt and line if necessary, but doesn't
// reposition the cursor in order to allow a frequently-updating app to write
// the cursor change where it makes sense, regardless of changes to the user's
// input.
func (p *AbsPrompt) WriteChangesNoCursor() {
	line, pos := p.LinePos()
	p.pos = pos

	if !p.prompted {
		p.PrintPrompt()
		p.prompted = true
	}

	if p.line != line {
		prevLine := p.line
		p.line = line
		p.PrintLine()

		lpl := len(prevLine)
		ll := len(line)
		bigger := lpl - ll
		if bigger > 0 {
			fmt.Fprintf(p.Out, strings.Repeat(" ", bigger))
			p.pos += bigger
		}
	}
}

// printAt moves to the position dx spaces from the start of the prompt's X
// location and prints a string
func (p *AbsPrompt) printAt(dx int, s string) {
	fmt.Fprintf(p.Out, "\x1b[%d;%dH%s", p.y, p.x+dx, s)
}

// PrintPrompt moves to the x/y coordinates of the prompt and prints the
// prompt string
func (p *AbsPrompt) PrintPrompt() {
	p.printAt(0, p.prompt)
	p.pos = 0
}

// PrintLine gets the current line and prints it to the screen just after the
// prompt location
func (p *AbsPrompt) PrintLine() {
	p.line, _ = p.LinePos()
	p.printAt(p.promptWidth, p.line)
	p.pos = len(p.line)
}

// PrintCursorMovement sends the ANSI escape sequence for moving the cursor
func (p *AbsPrompt) PrintCursorMovement() {
	p.pos = p.Pos()
	p.printAt(p.promptWidth+p.pos, "")
}