Enhancing the editor to correctly handle unicode.

widgets/textinput/editor.go

@@ -60,6 +60,7 @@ func (fd *fieldData) cellsBefore(cells, endIdx int) int {
 	for i := endIdx; i > 0; i-- {
 		prev := (*fd)[i-1]
 		width := runewidth.RuneWidth(prev)
+
 		if usedCells+width > cells {
 			return i
 		}
@@ -88,165 +89,131 @@ func (fd *fieldData) cellsAfter(cells, startIdx int) int {
 	return len(*fd)
 }
 
-// startVisible asserts whether the first rune is within the visible range.
-func (fd *fieldData) startVisible(vr *visibleRange) bool {
-	return vr.startIdx == 0
-}
-
-// endVisible asserts whether the last rune is within the visible range.
-// The last position in the visible range is reserved for the cursor or an
-// arrow.
-func (fd *fieldData) endVisible(vr *visibleRange) bool {
-	return vr.endIdx-1 >= len(*fd)
-}
-
 // minForArrows is the smallest number of cells in the window where we can
 // indicate hidden text with left and right arrow.
 const minForArrows = 3
 
+// curMinIdx returns the lowest acceptable index for cursor position that is
+// still within the visible range.
+func curMinIdx(start, cells int) int {
+	if start == 0 || cells < minForArrows {
+		// The very first rune is visible, so the cursor can go all the way to
+		// the start.
+		return start
+	}
+
+	// When the first rune isn't visible, the cursor cannot go on the first
+	// cell in the visible range since it contains the left arrow.
+	return start + 1
+}
+
+// curMaxIdx returns the highest acceptable index for cursor position that is
+// still within the visible range given the number of runes in data.
+func curMaxIdx(start, end, cells, runeCount int) int {
+	if end == runeCount+1 || cells < minForArrows {
+		// The last rune is visible, so the cursor can go all the way to the
+		// end.
+		return end - 1
+	}
+
+	// When the last rune isn't visible, the cursor cannot go on the last cell
+	// in the window that is reserved for appending text, since it contains the
+	// right arrow.
+	return end - 2
+}
+
+// shiftLeft shifts the visible range left so that it again contains the
+// cursor.
+func (fd *fieldData) shiftLeft(start, end, cells, curDataPos int) (int, int) {
+	var startIdx int
+	switch {
+	case curDataPos == 0 || cells < minForArrows:
+		startIdx = curDataPos
+
+	default:
+		startIdx = curDataPos - 1
+	}
+	forRunes := cells - 1
+	endIdx := fd.cellsAfter(forRunes, startIdx)
+	endIdx++ // Space for the cursor.
+
+	return startIdx, endIdx
+}
+
+// shiftRight shifts the visible range right so that it again contains the
+// cursor.
+func (fd *fieldData) shiftRight(start, end, cells, curDataPos int) (int, int) {
+	var endIdx int
+	switch dataLen := len(*fd); {
+	case curDataPos == dataLen:
+		// Cursor is in the empty space after the data.
+		// Print all runes until the end of data.
+		endIdx = dataLen
+
+	default:
+		// Cursor is within the data, print all runes including the one the
+		// cursor is on.
+		endIdx = curDataPos + 1
+	}
+
+	forRunes := cells - 1
+	startIdx := fd.cellsBefore(forRunes, endIdx)
+	endIdx = fd.cellsAfter(forRunes, startIdx)
+	endIdx++ // Space for the cursor.
+
+	return startIdx, endIdx
+}
+
 // runesIn returns runes that are in the visible range.
-func (fd *fieldData) runesIn(vr *visibleRange) string {
+// This might return smaller number of runes than the size of the range,
+// depending on the width of the individual runes.
+func (fd *fieldData) runesIn(firstRune, curPos, cells int) (string, int) {
+	forRunes := cells - 1 // One cell reserved for the cursor when appending.
+
+	start := firstRune
+	end := fd.cellsAfter(forRunes, start)
+	end++
+
+	if start > 0 && end-1 >= len(*fd) {
+		end = len(*fd)
+		start = fd.cellsBefore(forRunes, end)
+		end++ // Space for the cursor within the visible range.
+	}
+
+	if curPos < curMinIdx(start, cells) {
+		start, end = fd.shiftLeft(start, end, cells, curPos)
+	} else if curPos > curMaxIdx(start, end, cells, len(*fd)) {
+		start, end = fd.shiftRight(start, end, cells, curPos)
+	}
+
 	var runes []rune
-	for i, r := range (*fd)[vr.startIdx:] {
-		if i+vr.startIdx > vr.endIdx-2 {
+	for i, r := range (*fd)[start:] {
+		if i+start > end-2 {
 			break
 		}
 		runes = append(runes, r)
 	}
+	//log.Printf("runes: %v", string(runes))
 
-	useArrows := vr.cells() >= minForArrows
+	useArrows := cells >= minForArrows
 	var b strings.Builder
 	for i, r := range runes {
 		switch {
-		case useArrows && i == 0 && !fd.startVisible(vr):
+		case useArrows && i == 0 && start > 0:
 			b.WriteRune('⇦')
+			if rw := runewidth.RuneWidth(r); rw == 2 {
+				b.WriteRune('⇦')
+			}
 
 		default:
 			b.WriteRune(r)
 		}
 	}
 
-	if useArrows && !fd.endVisible(vr) {
+	if useArrows && end-1 < len(*fd) {
 		b.WriteRune('⇨')
 	}
-	return b.String()
-}
-
-// visibleRange represents a range of currently visible cells.
-// Visible cells are all cells whose index falls within:
-//   startIdx <= idx < endIdx
-// Not all of these cells are available for runes, the last cell is reserved
-// for the cursor to append data or for an arrow indicating that the text is
-// scrolling. See forRunes().
-type visibleRange struct {
-	startIdx int
-	endIdx   int
-}
-
-// forRunes returns the number of cells that are usable for runes.
-// Part of the visible range is reserved for the cursor at the end of the data.
-func (vr *visibleRange) forRunes() int {
-	cells := vr.cells()
-	if cells < 1 {
-		return 0
-	}
-	return cells - 1 // One cell reserved for the cursor at the end.
-}
-
-// cells returns the number of cells in the range.
-func (vr *visibleRange) cells() int {
-	return vr.endIdx - vr.startIdx
-}
-
-// contains asserts whether the provided index is in the range.
-func (vr *visibleRange) contains(idx int) bool {
-	return idx >= vr.startIdx && idx < vr.endIdx
-}
-
-// set sets the visible range from the start to the end index.
-func (vr *visibleRange) set(startIdx, endIdx int) {
-	vr.startIdx = startIdx
-	vr.endIdx = endIdx
-}
-
-// curMinIdx returns the lowest acceptable index for cursor position that is
-// still within the visible range.
-func (vr *visibleRange) curMinIdx() int {
-	if vr.cells() == 0 {
-		return vr.startIdx
-	}
-
-	if vr.startIdx == 0 || vr.cells() < minForArrows {
-		// The very first rune is visible, so the cursor can go all the way to
-		// the start.
-		return vr.startIdx
-	}
-
-	// When the first rune isn't visible, the cursor cannot go on the first
-	// cell in the visible range since it contains the left arrow.
-	return vr.startIdx + 1
-}
-
-// curMaxIdx returns the highest acceptable index for cursor position that is
-// still within the visible range given the number of runes in data.
-func (vr *visibleRange) curMaxIdx(runeCount int) int {
-	if vr.cells() == 0 {
-		return vr.startIdx
-	}
-
-	if vr.endIdx == runeCount || vr.endIdx == runeCount+1 || vr.cells() < minForArrows {
-		// The last rune is visible, so the cursor can go all the way to the
-		// end.
-		return vr.endIdx - 1
-	}
-
-	// When the last rune isn't visible, the cursor cannot go on the last cell
-	// in the window that is reserved for appending text, since it contains the
-	// right arrow.
-	return vr.endIdx - 2
-}
-
-// normalizeToWidth normalizes the visible range, handles cases where the width of the
-// text input field changed (terminal resize).
-func (vr *visibleRange) normalizeToWidth(width int) {
-	switch {
-	case width < vr.cells():
-		diff := vr.cells() - width
-		vr.startIdx += diff
-
-	case width > vr.cells():
-		diff := width - vr.cells()
-		vr.startIdx -= diff
-	}
-
-	if vr.startIdx < 0 {
-		vr.endIdx += -1 * vr.startIdx
-		vr.startIdx = 0
-	}
-}
-
-// normalizeToiData normalizes the visible range, handles cases where the
-// length of the data decreased due to deletion of some runes.
-func (vr *visibleRange) normalizeToData(fd fieldData) {
-	if vr.endIdx <= len(fd) || vr.startIdx == 0 {
-		// Nothing to do when data fills the range or the range already starts
-		// all the way left.
-		return
-	}
-
-	endIdx := len(fd)
-	startIdx := fd.cellsBefore(vr.forRunes(), endIdx)
-	endIdx++ // Space for the cursor within the visible range.
-	vr.set(startIdx, endIdx)
-}
-
-// curRelative returns the relative position of the cursor within the visible
-// range. Returns an error if the cursos isn't inside the visible range.
-func (vr *visibleRange) curRelative(curDataPos int) (int, error) {
-	if !vr.contains(curDataPos) {
-		return 0, fmt.Errorf("curDataPos %d isn't inside %#v", curDataPos, *vr)
-	}
-	return curDataPos - vr.startIdx, nil
+	return b.String(), start
 }
 
 // fieldEditor maintains the cursor position and allows editing of the data in
@@ -261,93 +228,51 @@ type fieldEditor struct {
 	// possible.
 	curDataPos int
 
-	// visible is the currently visible range.
-	visible *visibleRange
+	// firstRune is the index of the first displayed rune in the text input
+	// field.
+	firstRune int
 }
 
 // newFieldEditor returns a new fieldEditor instance.
 func newFieldEditor() *fieldEditor {
-	return &fieldEditor{
-		visible: &visibleRange{},
-	}
-}
-
-// shiftLeft shifts the visible range left so that it again contains the
-// cursor.
-func (fe *fieldEditor) shiftLeft() {
-	var startIdx int
-	switch {
-	case fe.curDataPos == 0 || fe.visible.cells() < minForArrows:
-		startIdx = fe.curDataPos
-
-	default:
-		startIdx = fe.curDataPos - 1
-	}
-	endIdx := fe.data.cellsAfter(fe.visible.forRunes(), startIdx)
-	endIdx++ // Space for the cursor.
-
-	gotCells := endIdx - startIdx
-	if fe.visible.cells() >= minForArrows && gotCells < minForArrows {
-		// The plan was to hide the first rune under an arrow.
-		// However after looking at the actual runes in the range, some took
-		// more space than one cell (full-width runes) and we have lost the
-		// space for the arrow, so shift the range by one.
-		startIdx++
-		endIdx++
-	}
-	fe.visible.set(startIdx, endIdx)
-}
-
-// shiftRight shifts the visible range right so that it again contains the
-// cursor.
-func (fe *fieldEditor) shiftRight() {
-	var endIdx int
-	switch dataLen := len(fe.data); {
-	case fe.curDataPos == dataLen:
-		// Cursor is in the empty space after the data.
-		// Print all runes until the end of data.
-		endIdx = dataLen
-
-	default:
-		// Cursor is within the data, print all runes including the one the
-		// cursor is on.
-		endIdx = fe.curDataPos + 1
-	}
-
-	startIdx := fe.data.cellsBefore(fe.visible.forRunes(), endIdx)
-	endIdx++ // Space for the cursor within the visible range.
-	fe.visible.set(startIdx, endIdx)
-}
-
-// toCursor shifts the visible range to the cursor if it scrolled out of view.
-// This is a no-op if the cursor is inside the range.
-func (fe *fieldEditor) toCursor() {
-	switch {
-	case fe.curDataPos < fe.visible.curMinIdx():
-		fe.shiftLeft()
-	case fe.curDataPos > fe.visible.curMaxIdx(len(fe.data)):
-		fe.shiftRight()
-	}
+	return &fieldEditor{}
 }
 
 // minFieldWidth is the minimum supported width of the text input field.
 const minFieldWidth = 4
 
+// curCell returns the index of the cell the cursor is in within the text input field.
+func (fe *fieldEditor) curCell(width int) int {
+	if width == 0 {
+		return 0
+	}
+	// The index of rune within the visible range the cursor is at.
+	runeNum := fe.curDataPos - fe.firstRune
+
+	cellNum := 0
+	rn := 0
+	for i, r := range fe.data {
+		if i < fe.firstRune {
+			continue
+		}
+		if rn >= runeNum {
+			break
+		}
+		rn++
+		cellNum += runewidth.RuneWidth(r)
+	}
+	return cellNum
+}
+
 // viewFor returns the currently visible data inside a text field with the
 // specified width and the cursor position within the field.
 func (fe *fieldEditor) viewFor(width int) (string, int, error) {
 	if min := minFieldWidth; width < min { // One for left arrow, two for one full-width rune and one for the cursor.
 		return "", -1, fmt.Errorf("width %d is too small, the minimum is %d", width, min)
 	}
-	fe.visible.normalizeToWidth(width)
-	fe.visible.normalizeToData(fe.data)
-	fe.toCursor()
-
-	cur, err := fe.visible.curRelative(fe.curDataPos)
-	if err != nil {
-		return "", 0, err
-	}
-	return fe.data.runesIn(fe.visible), cur, nil
+	runes, start := fe.data.runesIn(fe.firstRune, fe.curDataPos, width)
+	fe.firstRune = start
+	return runes, fe.curCell(width), nil
 }
 
 // content returns the string content in the field editor.
@@ -368,7 +293,7 @@ func (fe *fieldEditor) insert(r rune) {
 		return
 	}
 	fe.data.insertAt(fe.curDataPos, r)
-	fe.curDataPos += rw
+	fe.curDataPos++
 }
 
 // delete deletes the rune at the current position of the cursor.