Adds TabWidthMeasurer (#360)

* Adds TabWidthMeasurer

* Fixes typo

Author: simonbs

Sources/Runestone/Library/TabWidthMeasurer.swift

@@ -0,0 +1,12 @@
+import UIKit
+
+enum TabWidthMeasurer {
+    static func tabWidth(tabLength: Int, font: UIFont) -> CGFloat {
+        let str = String(repeating: " ", count: tabLength)
+        let maxSize = CGSize(width: CGFloat.greatestFiniteMagnitude, height: .greatestFiniteMagnitude)
+        let options: NSStringDrawingOptions = [.usesFontLeading, .usesLineFragmentOrigin]
+        let attributes: [NSAttributedString.Key: Any] = [.font: font]
+        let bounds = str.boundingRect(with: maxSize, options: options, attributes: attributes, context: nil)
+        return round(bounds.size.width)
+    }
+}

Sources/Runestone/TextView/Indent/IndentController.swift

@@ -30,12 +30,7 @@ final class IndentController {
         if let tabWidth = _tabWidth {
             return tabWidth
         } else {
-            let str = String(repeating: " ", count: indentStrategy.tabLength)
-            let maxSize = CGSize(width: CGFloat.greatestFiniteMagnitude, height: .greatestFiniteMagnitude)
-            let options: NSStringDrawingOptions = [.usesFontLeading, .usesLineFragmentOrigin]
-            let attributes: [NSAttributedString.Key: Any] = [.font: indentFont]
-            let bounds = str.boundingRect(with: maxSize, options: options, attributes: attributes, context: nil)
-            let tabWidth = round(bounds.size.width)
+            let tabWidth = TabWidthMeasurer.tabWidth(tabLength: indentStrategy.tabLength, font: indentFont)
             if tabWidth != _tabWidth {
                 _tabWidth = tabWidth
                 delegate?.indentControllerDidUpdateTabWidth(self)

Sources/Runestone/TextView/Indent/IndentStrategy.swift

@@ -2,7 +2,7 @@ import Foundation
 
 /// Strategy to use when indenting text.
 public enum IndentStrategy: Equatable {
-    /// Indent using tabs. The length specified length is used to determine the width of the tab measured in space characers.
+    /// Indent using tabs. The specified length is used to determine the width of the tab measured in space characers.
     case tab(length: Int)
     /// Indent using a number of spaces.
     case space(length: Int)