editbox.go

package jiraui

import (
	"unicode/utf8"
)

const tabstop_length = 8

type EditBox struct {
	text           []byte
	line_voffset   int
	cursor_boffset int // cursor offset in bytes
	cursor_voffset int // visual cursor offset in termbox cells
	cursor_coffset int // cursor offset in unicode code points
}

func byte_slice_grow(s []byte, desired_cap int) []byte {
	if cap(s) < desired_cap {
		ns := make([]byte, len(s), desired_cap)
		copy(ns, s)
		return ns
	}
	return s
}

func byte_slice_remove(text []byte, from, to int) []byte {
	size := to - from
	copy(text[from:], text[to:])
	text = text[:len(text)-size]
	return text
}

func byte_slice_insert(text []byte, offset int, what []byte) []byte {
	n := len(text) + len(what)
	text = byte_slice_grow(text, n)
	text = text[:n]
	copy(text[offset+len(what):], text[offset:])
	copy(text[offset:], what)
	return text
}

func decodeTermuiKbdStringToRune(str string) rune {
	r, _ := utf8.DecodeRuneInString(str) // should be a single rune
	return r
}

func (eb *EditBox) InsertRune(r rune) {
	var buf [utf8.UTFMax]byte
	n := utf8.EncodeRune(buf[:], r)
	eb.text = byte_slice_insert(eb.text, eb.cursor_boffset, buf[:n])
	eb.MoveCursorOneRuneForward()
}

func (eb *EditBox) DeleteRuneBackward() {
	if eb.cursor_boffset == 0 {
		return
	}
	eb.MoveCursorOneRuneBackward()
	_, size := eb.RuneUnderCursor()
	eb.text = byte_slice_remove(eb.text, eb.cursor_boffset, eb.cursor_boffset+size)
}

func (eb *EditBox) MoveCursorOneRuneBackward() {
	if eb.cursor_boffset == 0 {
		return
	}
	_, size := eb.RuneBeforeCursor()
	eb.MoveCursorTo(eb.cursor_boffset - size)
}

func (eb *EditBox) MoveCursorOneRuneForward() {
	if eb.cursor_boffset == len(eb.text) {
		return
	}
	_, size := eb.RuneUnderCursor()
	eb.MoveCursorTo(eb.cursor_boffset + size)
}

func (eb *EditBox) RuneUnderCursor() (rune, int) {
	return utf8.DecodeRune(eb.text[eb.cursor_boffset:])
}

func (eb *EditBox) RuneBeforeCursor() (rune, int) {
	return utf8.DecodeLastRune(eb.text[:eb.cursor_boffset])
}

func (eb *EditBox) MoveCursorTo(boffset int) {
	eb.cursor_boffset = boffset
	eb.cursor_voffset, eb.cursor_coffset = voffset_coffset(eb.text, boffset)
}

func (eb *EditBox) MoveCursorToEnd() {
	eb.MoveCursorTo(len(eb.text))
}

func rune_advance_len(r rune, pos int) int {
	if r == '\t' {
		return tabstop_length - pos%tabstop_length
	}
	return 1
}

func voffset_coffset(text []byte, boffset int) (voffset, coffset int) {
	text = text[:boffset]
	for len(text) > 0 {
		r, size := utf8.DecodeRune(text)
		text = text[size:]
		coffset += 1
		voffset += rune_advance_len(r, voffset)
	}
	return
}