Implement if and ifnot tags

Closes #3

Stencil/Node.swift

@@ -154,3 +154,66 @@ public class ForNode : Node {
         return (result, nil)
     }
 }
+
+public class IfNode : Node {
+    public let variable:Variable
+    public let trueNodes:[Node]
+    public let falseNodes:[Node]
+
+    public class func parse(parser:TokenParser, token:Token) -> Node {
+        let variable = token.components()[1]
+
+        let trueNodes = parser.parse(until(["endif", "else"]))
+        var falseNodes = [Node]()
+
+        if let token = parser.nextToken() {
+            if token.contents == "else" {
+                falseNodes = parser.parse(until(["endif"]))
+                parser.nextToken()
+            }
+        }
+
+        return IfNode(variable: variable, trueNodes: trueNodes, falseNodes: falseNodes)
+    }
+
+    public class func parse_ifnot(parser:TokenParser, token:Token) -> Node {
+        let variable = token.components()[1]
+
+        let falseNodes = parser.parse(until(["endif", "else"]))
+        var trueNodes = [Node]()
+
+        if let token = parser.nextToken() {
+            if token.contents == "else" {
+                trueNodes = parser.parse(until(["endif"]))
+                parser.nextToken()
+            }
+        }
+
+        return IfNode(variable: variable, trueNodes: trueNodes, falseNodes: falseNodes)
+    }
+
+    public init(variable:String, trueNodes:[Node], falseNodes:[Node]) {
+        self.variable = Variable(variable)
+        self.trueNodes = trueNodes
+        self.falseNodes = falseNodes
+    }
+
+    public func render(context: Context) -> (String?, Error?) {
+        let result: AnyObject? = variable.resolve(context)
+        var truthy = false
+
+        if let result = result as? [AnyObject] {
+            if result.count > 0 {
+                truthy = true
+            }
+        } else if let result: AnyObject = result {
+            truthy = true
+        }
+
+        context.push()
+        let (string, error) = renderNodes(truthy ? trueNodes : falseNodes, context)
+        context.pop()
+
+        return (string, error)
+    }
+}

Stencil/Parser.swift

@@ -28,6 +28,8 @@ public class TokenParser {
         self.tokens = tokens
         tags["for"] = ForNode.parse
         tags["now"] = NowNode.parse
+        tags["if"] = IfNode.parse
+        tags["ifnot"] = IfNode.parse_ifnot
     }
 
     public func parse() -> [Node] {

StencilTests/NodeTests.swift

@@ -86,3 +86,71 @@ class ForNodeTests: NodeTests {
         XCTAssertEqual(result.0!, "123")
     }
 }
+
+class IfNodeTests: NodeTests {
+
+    // MARK: Parsing
+
+    func testParseIf() {
+        let tokens = [
+            Token.Block(value: "if value"),
+                Token.Text(value: "true"),
+            Token.Block(value: "else"),
+                Token.Text(value: "false"),
+            Token.Block(value: "endif")
+        ]
+
+        let parser = TokenParser(tokens: tokens)
+        let nodes = parser.parse()
+        let node = nodes.first! as IfNode
+        let trueNode = node.trueNodes.first! as TextNode
+        let falseNode = node.falseNodes.first! as TextNode
+
+        XCTAssertEqual(nodes.count, 1)
+        XCTAssertEqual(node.variable.variable, "value")
+        XCTAssertEqual(node.trueNodes.count, 1)
+        XCTAssertEqual(trueNode.text, "true")
+        XCTAssertEqual(node.falseNodes.count, 1)
+        XCTAssertEqual(falseNode.text, "false")
+    }
+
+    func testParseIfNot() {
+        let tokens = [
+            Token.Block(value: "ifnot value"),
+                Token.Text(value: "false"),
+            Token.Block(value: "else"),
+                Token.Text(value: "true"),
+            Token.Block(value: "endif")
+        ]
+
+        let parser = TokenParser(tokens: tokens)
+        let nodes = parser.parse()
+        let node = nodes.first! as IfNode
+        let trueNode = node.trueNodes.first! as TextNode
+        let falseNode = node.falseNodes.first! as TextNode
+
+        XCTAssertEqual(nodes.count, 1)
+        XCTAssertEqual(node.variable.variable, "value")
+        XCTAssertEqual(node.trueNodes.count, 1)
+        XCTAssertEqual(trueNode.text, "true")
+        XCTAssertEqual(node.falseNodes.count, 1)
+        XCTAssertEqual(falseNode.text, "false")
+    }
+
+    // MARK: Rendering
+
+    func testIfNodeRenderTruth() {
+        let node = IfNode(variable: "items", trueNodes: [TextNode(text: "true")], falseNodes: [TextNode(text: "false")])
+        let result = node.render(context)
+
+        XCTAssertEqual(result.0!, "true")
+    }
+
+    func testIfNodeRenderFalse() {
+        let node = IfNode(variable: "unknown", trueNodes: [TextNode(text: "true")], falseNodes: [TextNode(text: "false")])
+        let result = node.render(context)
+
+        XCTAssertEqual(result.0!, "false")
+    }
+
+}