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cursor.go
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cursor.go
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// +build !windows
package terminal
import (
"bufio"
"bytes"
"fmt"
"io"
"regexp"
"strconv"
)
var COORDINATE_SYSTEM_BEGIN Short = 1
var dsrPattern = regexp.MustCompile(`\x1b\[(\d+);(\d+)R$`)
type Cursor struct {
In FileReader
Out FileWriter
}
// Up moves the cursor n cells to up.
func (c *Cursor) Up(n int) {
fmt.Fprintf(c.Out, "\x1b[%dA", n)
}
// Down moves the cursor n cells to down.
func (c *Cursor) Down(n int) {
fmt.Fprintf(c.Out, "\x1b[%dB", n)
}
// Forward moves the cursor n cells to right.
func (c *Cursor) Forward(n int) {
fmt.Fprintf(c.Out, "\x1b[%dC", n)
}
// Back moves the cursor n cells to left.
func (c *Cursor) Back(n int) {
fmt.Fprintf(c.Out, "\x1b[%dD", n)
}
// NextLine moves cursor to beginning of the line n lines down.
func (c *Cursor) NextLine(n int) {
c.Down(1)
c.HorizontalAbsolute(0)
}
// PreviousLine moves cursor to beginning of the line n lines up.
func (c *Cursor) PreviousLine(n int) {
c.Up(1)
c.HorizontalAbsolute(0)
}
// HorizontalAbsolute moves cursor horizontally to x.
func (c *Cursor) HorizontalAbsolute(x int) {
fmt.Fprintf(c.Out, "\x1b[%dG", x)
}
// Show shows the cursor.
func (c *Cursor) Show() {
fmt.Fprint(c.Out, "\x1b[?25h")
}
// Hide hide the cursor.
func (c *Cursor) Hide() {
fmt.Fprint(c.Out, "\x1b[?25l")
}
// Move moves the cursor to a specific x,y location.
func (c *Cursor) Move(x int, y int) {
fmt.Fprintf(c.Out, "\x1b[%d;%df", x, y)
}
// Save saves the current position
func (c *Cursor) Save() {
fmt.Fprint(c.Out, "\x1b7")
}
// Restore restores the saved position of the cursor
func (c *Cursor) Restore() {
fmt.Fprint(c.Out, "\x1b8")
}
// for comparability purposes between windows
// in unix we need to print out a new line on some terminals
func (c *Cursor) MoveNextLine(cur *Coord, terminalSize *Coord) {
if cur.Y == terminalSize.Y {
fmt.Fprintln(c.Out)
}
c.NextLine(1)
}
// Location returns the current location of the cursor in the terminal
func (c *Cursor) Location(buf *bytes.Buffer) (*Coord, error) {
// ANSI escape sequence for DSR - Device Status Report
// https://en.wikipedia.org/wiki/ANSI_escape_code#CSI_sequences
fmt.Fprint(c.Out, "\x1b[6n")
// There may be input in Stdin prior to CursorLocation so make sure we don't
// drop those bytes.
var loc []int
var match string
for loc == nil {
// Reports the cursor position (CPR) to the application as (as though typed at
// the keyboard) ESC[n;mR, where n is the row and m is the column.
reader := bufio.NewReader(c.In)
text, err := reader.ReadSlice(byte('R'))
if err != nil {
return nil, err
}
loc = dsrPattern.FindStringIndex(string(text))
if loc == nil {
// After reading slice to byte 'R', the bufio Reader may have read more
// bytes into its internal buffer which will be discarded on next ReadSlice.
// We create a temporary buffer to read the remaining buffered slice and
// write them to output buffer.
buffered := make([]byte, reader.Buffered())
_, err = io.ReadFull(reader, buffered)
if err != nil {
return nil, err
}
// Stdin contains R that doesn't match DSR, so pass the bytes along to
// output buffer.
buf.Write(text)
buf.Write(buffered)
} else {
// Write the non-matching leading bytes to output buffer.
buf.Write(text[:loc[0]])
// Save the matching bytes to extract the row and column of the cursor.
match = string(text[loc[0]:loc[1]])
}
}
matches := dsrPattern.FindStringSubmatch(string(match))
if len(matches) != 3 {
return nil, fmt.Errorf("incorrect number of matches: %d", len(matches))
}
col, err := strconv.Atoi(matches[2])
if err != nil {
return nil, err
}
row, err := strconv.Atoi(matches[1])
if err != nil {
return nil, err
}
return &Coord{Short(col), Short(row)}, nil
}
func (cur Coord) CursorIsAtLineEnd(size *Coord) bool {
return cur.X == size.X
}
func (cur Coord) CursorIsAtLineBegin() bool {
return cur.X == COORDINATE_SYSTEM_BEGIN
}
// Size returns the height and width of the terminal.
func (c *Cursor) Size(buf *bytes.Buffer) (*Coord, error) {
// the general approach here is to move the cursor to the very bottom
// of the terminal, ask for the current location and then move the
// cursor back where we started
// hide the cursor (so it doesn't blink when getting the size of the terminal)
c.Hide()
defer c.Show()
// save the current location of the cursor
c.Save()
defer c.Restore()
// move the cursor to the very bottom of the terminal
c.Move(999, 999)
// ask for the current location
bottom, err := c.Location(buf)
if err != nil {
return nil, err
}
// since the bottom was calculated in the lower right corner, it
// is the dimensions we are looking for
return bottom, nil
}