Implement trim whitespace

Sources/Stencil/TrimBehaviour.swift

@@ -0,0 +1,70 @@
+import Foundation
+
+public struct TrimBehaviour: Equatable {
+  var leading: Trim
+  var trailing: Trim
+
+  public enum Trim {
+    /// nothing
+    case nothing
+
+    /// tabs and spaces
+    case whitespace
+
+    /// tabs and spaces and a single new line
+    case whitespaceAndOneNewLine
+
+    /// all tabs spaces and newlines
+    case whitespaceAndNewLines
+  }
+
+  public init(leading: Trim, trailing: Trim) {
+    self.leading = leading
+    self.trailing = trailing
+  }
+
+  /// doesn't touch newlines
+  public static let nothing = TrimBehaviour(leading: .nothing, trailing: .nothing)
+
+  /// removes whitespace before a block and whitespace and a single newline after a block
+  public static let smart = TrimBehaviour(leading: .whitespace, trailing: .whitespaceAndOneNewLine)
+
+  /// removes all whitespace and newlines before and after a block
+  public static let all = TrimBehaviour(leading: .whitespaceAndNewLines, trailing: .whitespaceAndNewLines)
+
+  static func leadingRegex(trim: Trim) -> NSRegularExpression {
+    switch trim {
+    case .nothing:
+      fatalError("No RegularExpression for none")
+    case .whitespace:
+      return Self.leadingWhitespace
+    case .whitespaceAndOneNewLine:
+      return Self.leadingWhitespaceAndOneNewLine
+    case .whitespaceAndNewLines:
+      return Self.leadingWhitespaceAndNewlines
+    }
+  }
+
+  static func trailingRegex(trim: Trim) -> NSRegularExpression {
+    switch trim {
+    case .nothing:
+      fatalError("No RegularExpression for none")
+    case .whitespace:
+      return Self.trailingWhitespace
+    case .whitespaceAndOneNewLine:
+      return Self.trailingWhitespaceAndOneNewLine
+    case .whitespaceAndNewLines:
+      return Self.trailingWhitespaceAndNewLines
+    }
+  }
+
+  // swiftlint:disable force_try
+  private static let leadingWhitespaceAndNewlines = try! NSRegularExpression(pattern: "^\\s+")
+  private static let trailingWhitespaceAndNewLines = try! NSRegularExpression(pattern: "\\s+$")
+
+  private static let leadingWhitespaceAndOneNewLine = try! NSRegularExpression(pattern: "^[ \t]*\n")
+  private static let trailingWhitespaceAndOneNewLine = try! NSRegularExpression(pattern: "\n[ \t]*$")
+
+  private static let leadingWhitespace = try! NSRegularExpression(pattern: "^[ \t]*")
+  private static let trailingWhitespace = try! NSRegularExpression(pattern: "[ \t]*$")
+}