Port code to truncate strings to visual width to Go

tools/wcswidth/truncate.go

@@ -0,0 +1,93 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package wcswidth
+
+import (
+	"errors"
+	"fmt"
+	"kitty/tools/utils"
+)
+
+var _ = fmt.Print
+
+type truncate_error struct {
+	pos, width int
+}
+
+func (self *truncate_error) Error() string {
+	return fmt.Sprint("Truncation at:", self.pos, " with width:", self.width)
+}
+
+type truncate_iterator struct {
+	w WCWidthIterator
+
+	pos, limit        int
+	limit_exceeded_at *truncate_error
+}
+
+func (self *truncate_iterator) handle_csi(body []byte) error {
+	self.pos += len(body) + 2
+	return nil
+}
+
+func (self *truncate_iterator) handle_st_terminated_escape_code(body []byte) error {
+	self.pos += len(body) + 4
+	return nil
+}
+
+func create_truncate_iterator() *truncate_iterator {
+	var ans truncate_iterator
+	ans.w.parser.HandleRune = ans.handle_rune
+	ans.w.parser.HandleCSI = ans.handle_csi
+	ans.w.parser.HandleOSC = ans.handle_st_terminated_escape_code
+	ans.w.parser.HandleAPC = ans.handle_st_terminated_escape_code
+	ans.w.parser.HandleDCS = ans.handle_st_terminated_escape_code
+	ans.w.parser.HandlePM = ans.handle_st_terminated_escape_code
+	ans.w.parser.HandleSOS = ans.handle_st_terminated_escape_code
+	return &ans
+}
+
+func (self *truncate_iterator) handle_rune(ch rune) error {
+	width := self.w.current_width
+	self.w.handle_rune(ch)
+	if self.limit_exceeded_at != nil {
+		if self.w.current_width <= self.limit { // emoji variation selectors can cause width to decrease
+			return &truncate_error{pos: self.pos + len(string(ch)), width: self.w.current_width}
+		}
+		return self.limit_exceeded_at
+	}
+	if self.w.current_width > self.limit {
+		self.limit_exceeded_at = &truncate_error{pos: self.pos, width: width}
+	}
+	self.pos += len(string(ch))
+	return nil
+}
+
+func (self *truncate_iterator) parse(b []byte) (ans int, width int) {
+	err := self.w.parser.Parse(b)
+	var te *truncate_error
+	if err != nil && errors.As(err, &te) {
+		return te.pos, te.width
+	}
+	if self.limit_exceeded_at != nil {
+		return self.limit_exceeded_at.pos, self.limit_exceeded_at.width
+	}
+	return len(b), self.w.current_width
+}
+
+func TruncateToVisualLengthWithWidth(text string, length int) (truncated string, width_of_truncated int) {
+	if length < 1 {
+		return text[:0], 0
+	}
+	t := create_truncate_iterator()
+	t.limit = length
+	t.limit_exceeded_at = nil
+	t.w.current_width = 0
+	truncate_point, width := t.parse(utils.UnsafeStringToBytes(text))
+	return text[:truncate_point], width
+}
+
+func TruncateToVisualLength(text string, length int) string {
+	ans, _ := TruncateToVisualLengthWithWidth(text, length)
+	return ans
+}