Code to move cursor left

tools/tui/readline/actions.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"kitty/tools/utils"
+	"kitty/tools/wcswidth"
 )
 
 var _ = fmt.Print
@@ -90,3 +91,32 @@ func (self *Readline) add_text(text string) {
 	}
 	self.lines = new_lines
 }
+
+func (self *Readline) move_cursor_left(amt uint, traverse_line_breaks bool) uint {
+	var amt_moved uint
+	for ; amt > 0; amt -= 1 {
+		if self.cursor_pos_in_line == 0 {
+			if !traverse_line_breaks || self.cursor_line == 0 {
+				return amt_moved
+			}
+			self.cursor_line -= 1
+			self.cursor_pos_in_line = len(self.lines[self.cursor_pos_in_line])
+			amt_moved += 1
+			continue
+		}
+		// This is an extremely inefficient algorithm but it does not matter since
+		// lines are not large.
+		line := self.lines[self.cursor_line]
+		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(runes) > 0 {
+			runes = runes[:len(runes)-1]
+			s := string(runes)
+			current_width = wcswidth.Stringwidth(s)
+		}
+		self.cursor_pos_in_line = len(string(runes))
+		amt_moved += 1
+	}
+	return amt_moved
+}

tools/tui/readline/actions_test.go

@@ -10,10 +10,9 @@ import (
 
 var _ = fmt.Print
 
-func TestAddText(t *testing.T) {
-	lp, _ := loop.New()
-
-	dt := func(initial string, prepare func(rl *Readline), expected ...string) {
+func test_func(t *testing.T) func(string, func(*Readline), ...string) *Readline {
+	return func(initial string, prepare func(rl *Readline), expected ...string) *Readline {
+		lp, _ := loop.New()
 		rl := New(lp, RlInit{})
 		rl.add_text(initial)
 		if prepare != nil {
@@ -34,8 +33,13 @@ func TestAddText(t *testing.T) {
 				t.Fatalf("Text not as expected for: %#v\n%#v != %#v", initial, expected[2], rl.all_text())
 			}
 		}
+		return rl
 	}
 
+}
+
+func TestAddText(t *testing.T) {
+	dt := test_func(t)
 	dt("test", nil, "test", "", "test")
 	dt("1234\n", nil, "1234\n", "", "1234\n")
 	dt("abcd", func(rl *Readline) {
@@ -50,5 +54,36 @@ func TestAddText(t *testing.T) {
 		rl.cursor_pos_in_line = 2
 		rl.add_text("12\n34")
 	}, "abcd\nxy12\n34", "z", "abcd\nxy12\n34z")
-
+}
+
+func TestCursorMovement(t *testing.T) {
+	dt := test_func(t)
+
+	left := func(rl *Readline, amt uint, moved_amt uint, traverse_line_breaks bool) {
+		actual := rl.move_cursor_left(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) {
+		left(rl, 2, 2, false)
+	}, "one\nt", "wo")
+	dt("one\ntwo", func(rl *Readline) {
+		left(rl, 4, 3, false)
+	}, "one\n", "two")
+	dt("one\ntwo", func(rl *Readline) {
+		left(rl, 4, 4, true)
+	}, "one", "\ntwo")
+	dt("one\ntwo", func(rl *Readline) {
+		left(rl, 7, 7, true)
+	}, "", "one\ntwo")
+	dt("one\ntwo", func(rl *Readline) {
+		left(rl, 10, 7, true)
+	}, "", "one\ntwo")
+	dt("one😀", func(rl *Readline) {
+		left(rl, 1, 1, false)
+	}, "one", "😀")
+	dt("oneä", func(rl *Readline) {
+		left(rl, 1, 1, false)
+	}, "one", "ä")
 }