From 5e5cae83914c792e29f332322c49212381617a9c Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 6 Oct 2022 13:54:18 +0530
Subject: [PATCH] Code to move cursor right

---
 tools/tui/readline/actions.go      | 40 ++++++++++++++++++++++++++++++
 tools/tui/readline/actions_test.go | 28 +++++++++++++++++++--
 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/tools/tui/readline/actions.go b/tools/tui/readline/actions.go
index 3d782af94..9f155291c 100644
--- a/tools/tui/readline/actions.go
+++ b/tools/tui/readline/actions.go
@@ -120,3 +120,43 @@ func (self *Readline) move_cursor_left(amt uint, traverse_line_breaks bool) uint
 	}
 	return amt_moved
 }
+
+func (self *Readline) move_cursor_right(amt uint, traverse_line_breaks bool) uint {
+	var amt_moved uint
+	for ; amt > 0; amt -= 1 {
+		line := self.lines[self.cursor_line]
+		if self.cursor_pos_in_line >= len(line) {
+			if !traverse_line_breaks || self.cursor_line == len(self.lines)-1 {
+				return amt_moved
+			}
+			self.cursor_line += 1
+			self.cursor_pos_in_line = 0
+			amt_moved += 1
+			continue
+		}
+		// This is an extremely inefficient algorithm but it does not matter since
+		// lines are not large.
+		before_runes := []rune(line[:self.cursor_pos_in_line])
+		after_runes := []rune(line[self.cursor_pos_in_line:])
+		orig_width := wcswidth.Stringwidth(line[:self.cursor_pos_in_line])
+		current_width := orig_width
+		for current_width == orig_width && len(after_runes) > 0 {
+			before_runes = append(before_runes, after_runes[0])
+			current_width = wcswidth.Stringwidth(string(before_runes))
+			after_runes = after_runes[1:]
+		}
+		// soak up any more runes that dont affect width
+		for len(after_runes) > 0 {
+			q := append(before_runes, after_runes[0])
+			w := wcswidth.Stringwidth(string(q))
+			if w != current_width {
+				break
+			}
+			after_runes = after_runes[1:]
+			before_runes = q
+		}
+		self.cursor_pos_in_line = len(string(before_runes))
+		amt_moved += 1
+	}
+	return amt_moved
+}
diff --git a/tools/tui/readline/actions_test.go b/tools/tui/readline/actions_test.go
index a1b250f66..2bbeed1cc 100644
--- a/tools/tui/readline/actions_test.go
+++ b/tools/tui/readline/actions_test.go
@@ -83,7 +83,31 @@ func TestCursorMovement(t *testing.T) {
 	dt("one😀", func(rl *Readline) {
 		left(rl, 1, 1, false)
 	}, "one", "😀")
-	dt("oneä", func(rl *Readline) {
+	dt("oneà", func(rl *Readline) {
 		left(rl, 1, 1, false)
-	}, "one", "ä")
+	}, "one", "à")
+
+	right := func(rl *Readline, amt uint, moved_amt uint, traverse_line_breaks bool) {
+		rl.cursor_line = 0
+		rl.cursor_pos_in_line = 0
+		actual := rl.move_cursor_right(amt, traverse_line_breaks)
+		if actual != moved_amt {
+			t.Fatalf("Failed to move cursor by %#v\nactual != expected: %#v != %#v", amt, actual, moved_amt)
+		}
+	}
+	dt("one\ntwo", func(rl *Readline) {
+		right(rl, 2, 2, false)
+	}, "on", "e\ntwo")
+	dt("one\ntwo", func(rl *Readline) {
+		right(rl, 4, 3, false)
+	}, "one", "\ntwo")
+	dt("one\ntwo", func(rl *Readline) {
+		right(rl, 4, 4, true)
+	}, "one\n", "two")
+	dt("😀one", func(rl *Readline) {
+		right(rl, 1, 1, false)
+	}, "😀", "one")
+	dt("àb", func(rl *Readline) {
+		right(rl, 1, 1, false)
+	}, "à", "b")
 }