chore: refactor padding functions (#254)

The `padLeft` and `padRight` functions were nearly identical and could
benefit from being refactored to share common code.

A new function called `pad` was added that applies padding based on the
sign of the amount of padding needed. A positive value applies padding
to the right side while a negative value applies padding to the left
side.

Issue: #252

Signed-off-by: Michael Lorant <michael.lorant@nine.com.au>

style.go

@@ -464,36 +464,23 @@ func (s Style) applyMargins(str string, inline bool) string {
 
 // Apply left padding.
 func padLeft(str string, n int, style *termenv.Style) string {
-	if n == 0 {
-		return str
-	}
-
-	sp := strings.Repeat(" ", n)
-	if style != nil {
-		sp = style.Styled(sp)
-	}
-
-	b := strings.Builder{}
-	l := strings.Split(str, "\n")
-
-	for i := range l {
-		b.WriteString(sp)
-		b.WriteString(l[i])
-		if i != len(l)-1 {
-			b.WriteRune('\n')
-		}
-	}
-
-	return b.String()
+	return pad(str, -n, style)
 }
 
 // Apply right padding.
 func padRight(str string, n int, style *termenv.Style) string {
+	return pad(str, n, style)
+}
+
+// pad adds padding to either the left or right side of a string.
+// Positive values add to the right side while negative values
+// add to the left side.
+func pad(str string, n int, style *termenv.Style) string {
 	if n == 0 {
 		return str
 	}
 
-	sp := strings.Repeat(" ", n)
+	sp := strings.Repeat(" ", abs(n))
 	if style != nil {
 		sp = style.Styled(sp)
 	}
@@ -502,8 +489,17 @@ func padRight(str string, n int, style *termenv.Style) string {
 	l := strings.Split(str, "\n")
 
 	for i := range l {
-		b.WriteString(l[i])
-		b.WriteString(sp)
+		switch {
+		// pad right
+		case n > 0:
+			b.WriteString(l[i])
+			b.WriteString(sp)
+		// pad left
+		default:
+			b.WriteString(sp)
+			b.WriteString(l[i])
+		}
+
 		if i != len(l)-1 {
 			b.WriteRune('\n')
 		}
@@ -525,3 +521,11 @@ func min(a, b int) int {
 	}
 	return b
 }
+
+func abs(a int) int {
+	if a < 0 {
+		return -a
+	}
+
+	return a
+}