[for] Provide forloop context, first, last and counter

Sources/Node.swift

@@ -158,8 +158,15 @@ public class ForNode : NodeType {
     let values = try variable.resolve(context)
 
     if let values = values as? [Any] where values.count > 0 {
-      return try values.map { item in
-        try context.push([loopVariable: item]) {
+      let count = values.count
+      return try values.enumerate().map { index, item in
+        let forContext = [
+          "first": index == 0,
+          "last": index == (count - 1),
+          "counter": index + 1,
+        ]
+
+        return try context.push([loopVariable: item, "forloop": forContext]) {
           try renderNodes(nodes, context)
         }
       }.joinWithSeparator("")

Specs/Nodes/ForNodeSpec.swift

@@ -20,4 +20,22 @@ describe("ForNode") {
     let node = ForNode(variable: "emptyItems", loopVariable: "item", nodes: nodes, emptyNodes: emptyNodes)
     try expect(try node.render(context)) == "empty"
   }
+
+  $0.it("renders the given nodes while providing if the item is first in the context") {
+    let nodes: [NodeType] = [VariableNode(variable: "item"), VariableNode(variable: "forloop.first")]
+    let node = ForNode(variable: "items", loopVariable: "item", nodes: nodes, emptyNodes: [])
+    try expect(try node.render(context)) == "112030"
+  }
+
+  $0.it("renders the given nodes while providing if the item is last in the context") {
+    let nodes: [NodeType] = [VariableNode(variable: "item"), VariableNode(variable: "forloop.last")]
+    let node = ForNode(variable: "items", loopVariable: "item", nodes: nodes, emptyNodes: [])
+    try expect(try node.render(context)) == "102031"
+  }
+
+  $0.it("renders the given nodes while providing item counter") {
+    let nodes: [NodeType] = [VariableNode(variable: "item"), VariableNode(variable: "forloop.counter")]
+    let node = ForNode(variable: "items", loopVariable: "item", nodes: nodes, emptyNodes: [])
+    try expect(try node.render(context)) == "112233"
+  }
 }