Add some test for vertical movement

tools/tui/readline/actions.go

@@ -183,7 +183,7 @@ func (self *Readline) move_cursor_vertically(amt int) (ans int) {
 			break
 		}
 	}
-	target_line_num := (cursor_line_num + amt + len(screen_lines)) % len(screen_lines)
+	target_line_num := utils.Min(utils.Max(0, cursor_line_num+amt), len(screen_lines)-1)
 	ans = target_line_num - cursor_line_num
 	if ans != 0 {
 		self.move_cursor_to_target_line(screen_lines[cursor_line_num], screen_lines[target_line_num])

tools/tui/readline/actions_test.go

@@ -176,6 +176,31 @@ func TestCursorMovement(t *testing.T) {
 	dt("àb", func(rl *Readline) {
 		right(rl, 1, 1, false)
 	}, "à", "b")
+
+	lp, _ := loop.New()
+	rl := New(lp, RlInit{Prompt: "$$ "})
+	rl.screen_width = 10
+
+	vert := func(amt int, moved_amt int, text_upto_cursor_pos string, initials ...Position) {
+		initial := Position{}
+		if len(initials) > 0 {
+			initial = initials[0]
+		}
+		rl.cursor = initial
+		actual := rl.move_cursor_vertically(amt)
+		if actual != moved_amt {
+			t.Fatalf("Failed to move cursor by %#v for: %#v \nactual != expected: %#v != %#v", amt, rl.AllText(), actual, moved_amt)
+		}
+		if diff := cmp.Diff(text_upto_cursor_pos, rl.text_upto_cursor_pos()); diff != "" {
+			t.Fatalf("Did not get expected screen lines for: %#v and cursor: %+v\n%s", rl.AllText(), initial, diff)
+		}
+	}
+
+	rl.ResetText()
+	rl.add_text("1234567xy\nabcd\n123")
+	vert(-1, -1, "1234567xy\nabc", Position{X: 3, Y: 2})
+	vert(-2, -2, "1234567xy", Position{X: 3, Y: 2})
+	vert(-30, -3, "123", Position{X: 3, Y: 2})
 }
 
 func TestEraseChars(t *testing.T) {

tools/utils/misc.go

@@ -53,3 +53,23 @@ func StableSortWithKey[T any, C constraints.Ordered](s []T, key func(a T) C) []T
 	sort.SliceStable(s, func(i, j int) bool { return mem[i] < mem[j] })
 	return s
 }
+
+func Max[T constraints.Ordered](a T, items ...T) (ans T) {
+	ans = a
+	for _, q := range items {
+		if q > ans {
+			ans = q
+		}
+	}
+	return ans
+}
+
+func Min[T constraints.Ordered](a T, items ...T) (ans T) {
+	ans = a
+	for _, q := range items {
+		if q < ans {
+			ans = q
+		}
+	}
+	return ans
+}