From ef7b3e75f4dc6b4741e9d58108833c2828627fcf Mon Sep 17 00:00:00 2001
From: Jack Mordaunt <jackmordaunt@gmail.com>
Date: Thu, 17 Sep 2020 15:48:32 +0800
Subject: [PATCH] widget: delete whole words with key modifier

Delete entire words with key modifier, ie "ctrl + delete".

Signed-off-by: Jack Mordaunt <jackmordaunt@gmail.com>
---
 widget/editor.go      | 59 +++++++++++++++++++++++++++++++++++++++++--
 widget/editor_test.go | 55 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 112 insertions(+), 2 deletions(-)

diff --git a/widget/editor.go b/widget/editor.go
index 3399a2cd..69b87965 100644
--- a/widget/editor.go
+++ b/widget/editor.go
@@ -276,9 +276,17 @@ func (e *Editor) command(k key.Event) bool {
 	case key.NameReturn, key.NameEnter:
 		e.append("\n")
 	case key.NameDeleteBackward:
-		e.Delete(-1)
+		if k.Modifiers == modSkip {
+			e.deleteWord(-1)
+		} else {
+			e.Delete(-1)
+		}
 	case key.NameDeleteForward:
-		e.Delete(1)
+		if k.Modifiers == modSkip {
+			e.deleteWord(1)
+		} else {
+			e.Delete(1)
+		}
 	case key.NameUpArrow:
 		e.moveLines(-1)
 	case key.NameDownArrow:
@@ -824,6 +832,53 @@ func (e *Editor) moveWord(distance int) {
 	}
 }
 
+// deleteWord the next word(s) in the specified direction.
+// Unlike moveWord, deleteWord treats whitespace as a word itself.
+// Positive is forward, negative is backward.
+// Absolute values greater than one will delete that many words.
+func (e *Editor) deleteWord(distance int) {
+	e.makeValid()
+	// split the distance information into constituent parts to be
+	// used independently.
+	words, direction := distance, 1
+	if distance < 0 {
+		words, direction = distance*-1, -1
+	}
+	// atEnd if offset is at or beyond either side of the buffer.
+	atEnd := func(offset int) bool {
+		idx := e.rr.caret + offset*direction
+		return idx <= 0 || idx >= e.rr.len()
+	}
+	// next returns the appropriate rune given the direction and offset.
+	next := func(offset int) (r rune) {
+		idx := e.rr.caret + offset*direction
+		if idx < 0 {
+			idx = 0
+		} else if idx > e.rr.len() {
+			idx = e.rr.len()
+		}
+		if direction < 0 {
+			r, _ = e.rr.runeBefore(idx)
+		} else {
+			r, _ = e.rr.runeAt(idx)
+		}
+		return r
+	}
+	var runes = 1
+	for ii := 0; ii < words; ii++ {
+		if r := next(runes); unicode.IsSpace(r) {
+			for r := next(runes); unicode.IsSpace(r) && !atEnd(runes); r = next(runes) {
+				runes += 1
+			}
+		} else {
+			for r := next(runes); !unicode.IsSpace(r) && !atEnd(runes); r = next(runes) {
+				runes += 1
+			}
+		}
+	}
+	e.Delete(runes * direction)
+}
+
 func (e *Editor) scrollToCaret() {
 	e.makeValid()
 	l := e.lines[e.caret.line]
diff --git a/widget/editor_test.go b/widget/editor_test.go
index 6c9b9e8d..e670d273 100644
--- a/widget/editor_test.go
+++ b/widget/editor_test.go
@@ -92,6 +92,7 @@ const (
 	moveEnd
 	moveCoord
 	moveWord
+	deleteWord
 	moveLast // Mark end; never generated.
 )
 
@@ -143,6 +144,8 @@ func TestEditorCaretConsistency(t *testing.T) {
 				e.moveCoord(image.Pt(int(x), int(y)))
 			case moveWord:
 				e.moveWord(int(distance))
+			case deleteWord:
+				e.deleteWord(int(distance))
 			default:
 				return false
 			}
@@ -203,6 +206,58 @@ func TestEditorMoveWord(t *testing.T) {
 		}
 	}
 }
+
+func TestEditorDeleteWord(t *testing.T) {
+	type Test struct {
+		Text   string
+		Start  int
+		Delete int
+
+		Want   int
+		Result string
+	}
+	tests := []Test{
+		{"", 0, 0, 0, ""},
+		{"", 0, -1, 0, ""},
+		{"", 0, 1, 0, ""},
+		{"hello", 0, -1, 0, "hello"},
+		{"hello", 0, 1, 0, ""},
+		{"hello world", 3, 1, 3, "hel world"},
+		{"hello world", 3, -1, 0, "lo world"},
+		{"hello world", 8, -1, 6, "hello rld"},
+		{"hello world", 8, 1, 8, "hello wo"},
+		{"hello    world", 3, 1, 3, "hel    world"},
+		{"hello    world", 3, 2, 3, "helworld"},
+		{"hello    world", 8, 1, 8, "hello   "},
+		{"hello    world", 8, -1, 5, "hello world"},
+		{"hello brave new world", 0, 3, 0, " new world"},
+	}
+	setup := func(t string) *Editor {
+		e := new(Editor)
+		gtx := layout.Context{
+			Ops:         new(op.Ops),
+			Constraints: layout.Exact(image.Pt(100, 100)),
+		}
+		cache := text.NewCache(gofont.Collection())
+		fontSize := unit.Px(10)
+		font := text.Font{}
+		e.SetText(t)
+		e.Layout(gtx, cache, font, fontSize)
+		return e
+	}
+	for ii, tt := range tests {
+		e := setup(tt.Text)
+		e.Move(tt.Start)
+		e.deleteWord(tt.Delete)
+		if e.rr.caret != tt.Want {
+			t.Fatalf("[%d] deleteWord: bad caret position: got %d, want %d", ii, e.rr.caret, tt.Want)
+		}
+		if e.Text() != tt.Result {
+			t.Fatalf("[%d] deleteWord: invalid result: got %q, want %q", ii, e.Text(), tt.Result)
+		}
+	}
+}
+
 func TestEditorNoLayout(t *testing.T) {
 	var e Editor
 	e.SetText("hi!\n")