Add editor packages

internal/editor/buffer/cursor.go

@@ -0,0 +1,218 @@
+package buffer
+
+import (
+	"log/slog"
+	"unicode/utf8"
+
+	"code.chimeric.al/dwrz/wen/internal/editor/buffer/glyph"
+)
+
+// Cursor tracks the position in a Buffer.
+// glyph is the 0-indexed terminal display column (tabs are 8 columns, wide
+// runes are 2 columns).
+// index is the 0-indexed byte offset in the current line's UTF-8 string.
+// line is the 0-indexed row in Buffer.lines.
+type Cursor struct {
+	glyph int
+	index int
+	line  int
+}
+
+func (b *Buffer) Cursor() Cursor {
+	return *b.cursor
+}
+
+func (c Cursor) Glyph() int {
+	return c.glyph
+}
+
+func (c Cursor) Index() int {
+	return c.index
+}
+
+func (c Cursor) Line() int {
+	return c.line
+}
+
+func (b *Buffer) CursorDown() {
+	b.log.Debug("↓ before", slog.Any("cursor", b.cursor))
+	defer b.log.Debug("↓ after", slog.Any("cursor", b.cursor))
+
+	// If we're on the last line, don't move down.
+	if b.cursor.line >= len(b.lines)-1 {
+		return
+	}
+
+	// Move to the next line.
+	b.cursor.line++
+
+	// Adjust the column.
+	var (
+		line   = b.CursorLine()
+		length = line.Length()
+		width  = line.Width()
+	)
+	switch {
+	// If we've moved to a shorter line, snap to its end.
+	case b.cursor.glyph > width:
+		b.cursor.index = length
+		b.cursor.glyph = width
+
+	default:
+		b.cursor.index, b.cursor.glyph = line.FindGlyphIndex(
+			b.cursor.glyph,
+		)
+	}
+}
+
+func (b *Buffer) CursorLeft() {
+	b.log.Debug("← before", slog.Any("cursor", b.cursor))
+	defer b.log.Debug("← after", slog.Any("cursor", b.cursor))
+
+	switch {
+	// If we're at the beginning of the line, move to the line above;
+	// unless we're at the start of the buffer.
+	case b.cursor.index == 0 && b.cursor.line > 0:
+		b.cursor.line--
+
+		line := b.CursorLine()
+		b.cursor.index = line.Length()
+		b.cursor.glyph = line.Width()
+
+	// Move left by one rune.
+	case b.cursor.index > 0:
+		var (
+			line = b.CursorLine()
+			r    rune
+			size int
+		)
+		// Reverse until we hit the start of a rune.
+		for i := b.cursor.index - 1; i >= 0; i-- {
+			r, size = line.DecodeRune(i)
+			if r != utf8.RuneError {
+				b.cursor.index -= size
+				b.cursor.glyph -= glyph.Width(r)
+				break
+			}
+		}
+	}
+}
+
+func (b *Buffer) CursorRight() {
+	b.log.Debug("→ before", slog.Any("cursor", b.cursor))
+	defer b.log.Debug("→ after", slog.Any("cursor", b.cursor))
+
+	var (
+		line   = b.CursorLine()
+		length = line.Length()
+	)
+
+	switch {
+	// If we're at the end of the line, move to the line below;
+	// unless we're at the end of the buffer.
+	case b.cursor.index == length && b.cursor.line < len(b.lines)-1:
+		b.cursor.line++
+		b.cursor.index = 0
+		b.cursor.glyph = 0
+
+	// Move the index right by one rune.
+	case b.cursor.index < length:
+		r, size := line.DecodeRune(b.cursor.index)
+		if r == utf8.RuneError {
+			b.cursor.index++
+			b.cursor.glyph += glyph.Width(r)
+		} else {
+			b.cursor.index += size
+			b.cursor.glyph += glyph.Width(r)
+		}
+	}
+}
+
+func (b *Buffer) CursorUp() {
+	b.log.Debug("↑ before", slog.Any("cursor", b.cursor))
+	defer b.log.Debug("↑ after", slog.Any("cursor", b.cursor))
+
+	// If we're on the first line, don't move up.
+	if b.cursor.line == 0 {
+		return
+	}
+
+	b.cursor.line--
+
+	// Adjust the column.
+	var (
+		line   = b.CursorLine()
+		length = line.Length()
+		width  = line.Width()
+	)
+	switch {
+	case b.cursor.glyph > width:
+		b.cursor.index = length
+		b.cursor.glyph = width
+
+	default:
+		b.cursor.index, b.cursor.glyph = line.FindGlyphIndex(
+			b.cursor.glyph,
+		)
+	}
+}
+
+func (b *Buffer) PageDown(height int) {
+	if b.cursor.line+height >= len(b.lines) {
+		b.cursor.line = len(b.lines) - 1
+	} else {
+		b.cursor.line += height
+	}
+
+	var (
+		line   = b.CursorLine()
+		length = line.Length()
+		width  = line.Width()
+	)
+	switch {
+	case b.cursor.glyph > width:
+		b.cursor.index = length
+		b.cursor.glyph = width
+
+	default:
+		b.cursor.index, b.cursor.glyph = line.FindGlyphIndex(
+			b.cursor.glyph,
+		)
+	}
+}
+
+func (b *Buffer) PageUp(height int) {
+	if b.cursor.line-height > 0 {
+		b.cursor.line -= height
+	} else {
+		b.cursor.line = 0
+	}
+
+	var (
+		line   = b.CursorLine()
+		length = line.Length()
+		width  = line.Width()
+	)
+	switch {
+	case b.cursor.glyph > width:
+		b.cursor.index = length
+		b.cursor.glyph = width
+
+	default:
+		b.cursor.index, b.cursor.glyph = line.FindGlyphIndex(
+			b.cursor.glyph,
+		)
+	}
+}
+
+func (b *Buffer) CursorHome() {
+	b.cursor.glyph = 0
+	b.cursor.index = 0
+}
+
+func (b *Buffer) CursorEnd() {
+	var line = b.CursorLine()
+
+	b.cursor.index = line.Length()
+	b.cursor.glyph = line.Width()
+}