Add PaddingWriter, an io.Writer proxy, that keeps lines at (least at) equal width

padding.go

@@ -0,0 +1,53 @@
+package gold
+
+import (
+	"io"
+)
+
+type PaddingFunc = func(w io.Writer)
+
+type PaddingWriter struct {
+	Forward *AnsiWriter
+	Padding uint
+	PadFunc PaddingFunc
+
+	lineLen int
+	ansi    bool
+}
+
+// Write is used to write content to the padding buffer.
+func (w *PaddingWriter) Write(b []byte) (int, error) {
+	for _, c := range string(b) {
+		if c == '\x1B' {
+			// ANSI escape sequence
+			w.ansi = true
+		} else if w.ansi {
+			if (c >= 0x40 && c <= 0x5a) || (c >= 0x61 && c <= 0x7a) {
+				// ANSI sequence terminated
+				w.ansi = false
+				w.lineLen--
+			}
+		} else {
+			if c == '\n' {
+				// end of current line
+				if w.Padding > 0 && uint(w.lineLen) < w.Padding {
+					for i := 0; i < int(w.Padding)-w.lineLen; i++ {
+						w.PadFunc(w.Forward)
+					}
+				}
+				w.Forward.ResetAnsi()
+				w.lineLen = -1
+			}
+		}
+
+		if !w.ansi {
+			w.lineLen++
+		}
+		_, err := w.Forward.Write([]byte(string(c)))
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	return len(b), nil
+}