Introduce variable filters

Stencil/Filters.swift

@@ -0,0 +1,33 @@
+func toString(value: Any?) -> String? {
+  if let value = value as? String {
+    return value
+  } else if let value = value as? CustomStringConvertible {
+    return value.description
+  }
+
+  return nil
+}
+
+func capitalise(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.capitalizedString
+  }
+
+  return value
+}
+
+func uppercase(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.uppercaseString
+  }
+
+  return value
+}
+
+func lowercase(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.lowercaseString
+  }
+
+  return value
+}

Stencil/Node.swift

@@ -46,22 +46,28 @@ public class TextNode : NodeType {
   }
 }
 
-public class VariableNode : NodeType {
-  public let variable:Variable
+public protocol Resolvable {
+  func resolve(context: Context) -> Any?
+}
 
-  public init(variable:Variable) {
+public class VariableNode : NodeType {
+  public let variable: Resolvable
+
+  public init(variable: Resolvable) {
     self.variable = variable
   }
 
-  public init(variable:String) {
+  public init(variable: String) {
     self.variable = Variable(variable)
   }
 
-  public func render(context:Context) throws -> String {
-    let result:AnyObject? = variable.resolve(context)
+  public func render(context: Context) throws -> String {
+    let result = variable.resolve(context)
 
     if let result = result as? String {
       return result
+    } else if let result = result as? CustomStringConvertible {
+      return result.description
     } else if let result = result as? NSObject {
       return result.description
     }
@@ -94,7 +100,7 @@ public class NowNode : NodeType {
 
   public func render(context: Context) throws -> String {
     let date = NSDate()
-    let format: AnyObject? = self.format.resolve(context)
+    let format = self.format.resolve(context)
     var formatter:NSDateFormatter?
 
     if let format = format as? NSDateFormatter {
@@ -212,7 +218,7 @@ public class IfNode : NodeType {
   }
 
   public func render(context: Context) throws -> String {
-    let result: AnyObject? = variable.resolve(context)
+    let result = variable.resolve(context)
     var truthy = false
 
     if let result = result as? [AnyObject] {

Stencil/Parser.swift

@@ -10,12 +10,15 @@ public func until(tags:[String])(parser:TokenParser, token:Token) -> Bool {
   return false
 }
 
+public typealias Filter = Any? -> Any?
+
 /// A class for parsing an array of tokens and converts them into a collection of Node's
 public class TokenParser {
   public typealias TagParser = (TokenParser, Token) throws -> NodeType
 
   private var tokens:[Token]
   private var tags = [String:TagParser]()
+  private var filters = [String: Filter]()
 
   public init(tokens:[Token]) {
     self.tokens = tokens
@@ -26,6 +29,9 @@ public class TokenParser {
     registerTag("include", parser: IncludeNode.parse)
     registerTag("extends", parser: ExtendsNode.parse)
     registerTag("block", parser: BlockNode.parse)
+    registerFilter("capitalize", filter: capitalise)
+    registerFilter("uppercase", filter: uppercase)
+    registerFilter("lowercase", filter: lowercase)
   }
 
   /// Registers a new template tag
@@ -40,6 +46,10 @@ public class TokenParser {
     })
   }
 
+  public func registerFilter(name: String, filter: Filter) {
+    filters[name] = filter
+  }
+
   /// Parse the given tokens into nodes
   public func parse() throws -> [NodeType] {
     return try parse(nil)
@@ -54,8 +64,8 @@ public class TokenParser {
       switch token {
       case .Text(let text):
         nodes.append(TextNode(text: text))
-      case .Variable(let variable):
-        nodes.append(VariableNode(variable: variable))
+      case .Variable:
+        nodes.append(VariableNode(variable: try compileFilter(token.contents)))
       case .Block:
         let tag = token.components().first
 
@@ -88,4 +98,16 @@ public class TokenParser {
   public func prependToken(token:Token) {
     tokens.insert(token, atIndex: 0)
   }
+
+  public func findFilter(name: String) throws -> Filter {
+    if let filter = filters[name] {
+      return filter
+    }
+
+    throw TemplateSyntaxError("Invalid filter '\(name)'")
+  }
+
+  func compileFilter(token: String) throws -> Resolvable {
+    return try FilterExpression(token: token, parser: self)
+  }
 }

Stencil/Variable.swift

@@ -1,8 +1,40 @@
 import Foundation
 
 
+class FilterExpression : Resolvable {
+  let filters: [Filter]
+  let variable: Variable
+
+  init(token: String, parser: TokenParser) throws {
+    let bits = token.componentsSeparatedByString("|")
+    if bits.isEmpty {
+      filters = []
+      variable = Variable("")
+      throw TemplateSyntaxError("Variable tags must include at least 1 argument")
+    }
+
+    variable = Variable(bits[0])
+    let filterBits = bits[1 ..< bits.endIndex]
+
+    do {
+      filters = try filterBits.map { try parser.findFilter($0) }
+    } catch {
+      filters = []
+      throw error
+    }
+  }
+
+  func resolve(context: Context) -> Any? {
+    let result = variable.resolve(context)
+
+    return filters.reduce(result) { x, y in
+      return y(x)
+    }
+  }
+}
+
 /// A structure used to represent a template variable, and to resolve it in a given context.
-public struct Variable : Equatable {
+public struct Variable : Equatable, Resolvable {
   public let variable:String
 
   /// Create a variable with a string representing the variable
@@ -15,11 +47,12 @@ public struct Variable : Equatable {
   }
 
   /// Resolve the variable in the given context
-  public func resolve(context:Context) -> AnyObject? {
+  public func resolve(context:Context) -> Any? {
     var current:AnyObject? = context
 
     if (variable.hasPrefix("'") && variable.hasSuffix("'")) || (variable.hasPrefix("\"") && variable.hasSuffix("\"")) {
-      return variable.substringWithRange(variable.startIndex.successor() ..< variable.endIndex.predecessor())
+      // String literal
+      return variable[variable.startIndex.successor() ..< variable.endIndex.predecessor()]
     }
 
     for bit in lookup() {