Add editor packages

internal/editor/buffer/line/line.go

@@ -0,0 +1,131 @@
+package line
+
+import (
+	"strings"
+	"unicode/utf8"
+
+	"code.chimeric.al/dwrz/wen/internal/editor/buffer/glyph"
+)
+
+type Line struct {
+	data string
+}
+
+func New(s string) *Line {
+	return &Line{data: s}
+}
+
+func (l *Line) DecodeRune(index int) (r rune, size int) {
+	return utf8.DecodeRuneInString(l.data[index:])
+}
+
+// FindGlyphIndex returns the byte index and display column (g) for a target
+// display column. If target falls inside a multi-column rune, it returns the
+// start of that rune. If target is past the end of the line, it returns the
+// byte length and total display width of the line.
+func (l *Line) FindGlyphIndex(target int) (index, g int) {
+	var li, lg int
+	for i, r := range l.data {
+		// We've reached the target.
+		if g == target {
+
+			return i, g
+		}
+		// We've gone too far.
+		// Return the preceding index and glyph.
+		if g > target {
+			return li, lg
+		}
+
+		// Otherwise, we haven't reached the target.
+		// Save this index and glyph.
+		li = i
+		lg = g
+
+		// Then increment the glyph.
+		g += glyph.Width(r)
+	}
+	// Target falls in-between the last glyph and the end of the line.
+	// Use the last glyph.
+	if target >= lg && target < g {
+		return li, lg
+	}
+
+	// We weren't able to find the glyph.
+	// Return the last possible index and glyph.
+	return len(l.data), g
+}
+
+// Length returns the byte length of the line's UTF-8 string.
+func (l *Line) Length() int {
+	return len(l.data)
+}
+
+// Render returns the visible substring starting at display column offset and
+// fitting within width display columns. Tabs are expanded to 8 spaces. If
+// offset splits a multi-column rune, the remaining columns of that rune are
+// padded with spaces.
+func (l *Line) Render(offset, width int) string {
+	if offset < 0 || width <= 0 {
+		return ""
+	}
+
+	var (
+		text = strings.ReplaceAll(l.data, "\t", "        ")
+		str  strings.Builder
+	)
+	for _, r := range text {
+		if r == utf8.RuneError {
+			continue
+		}
+
+		rw := glyph.Width(r)
+		if offset > 0 {
+			offset -= rw
+			if offset < 0 {
+				// The offset split a wide rune.
+				// Pad the remaining column.
+				pad := -offset
+				if pad > width {
+					pad = width
+				}
+				for i := 0; i < pad; i++ {
+					str.WriteRune(' ')
+				}
+				width -= pad
+				offset = 0
+			}
+			continue
+		}
+
+		if width-rw < 0 {
+			break
+		}
+
+		str.WriteRune(r)
+		width -= rw
+	}
+
+	return str.String()
+}
+
+func (l *Line) Runes() []rune {
+	return []rune(l.data)
+}
+
+func (l *Line) String() string {
+	return l.data
+}
+
+// Width returns the terminal display column width of the line.
+func (l *Line) Width() (count int) {
+	for _, r := range l.data {
+		rw := glyph.Width(r)
+		if r == utf8.RuneError {
+			continue
+		}
+		count += rw
+	}
+
+	return count
+}