Cthulhu is no longer a fork. Now it is a screen reader written in Golang.

internal/braille/regions.go

@@ -0,0 +1,42 @@
+package braille
+
+import (
+	"errors"
+	"strings"
+	"unicode/utf8"
+)
+
+// Region is one semantic piece of a braille line. Cursor is a zero-based rune
+// offset within Text, including the position just after the final rune.
+type Region struct {
+	Text   string
+	Cursor int
+}
+
+// Line follows Python Cthulhu's Line: regions are concatenated exactly as
+// supplied and one region may own the visible cursor. A focus of -1 hides it.
+type Line struct {
+	Regions []Region
+	Focus   int
+}
+
+func (line Line) Frame() (Frame, error) {
+	if line.Focus < -1 || line.Focus >= len(line.Regions) {
+		return Frame{}, errors.New("invalid focused braille region")
+	}
+	var text strings.Builder
+	cursor := -1
+	position := 0
+	for index, region := range line.Regions {
+		length := utf8.RuneCountInString(region.Text)
+		if index == line.Focus {
+			if region.Cursor < 0 || region.Cursor > length {
+				return Frame{}, errors.New("invalid braille region cursor")
+			}
+			cursor = position + region.Cursor
+		}
+		text.WriteString(region.Text)
+		position += length
+	}
+	return Frame{Text: text.String(), Cursor: cursor}, nil
+}