RestHelper.scala

/*
 * Copyright 2010-2011 WorldWide Conferencing, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.liftweb 
package http 
package rest 

import net.liftweb._
import actor.LAFuture
import json._
import common._
import util._
import scala.xml.{Elem, Node, Text}

/**
 * Mix this trait into a class to provide a list of REST helper methods
 */
trait RestHelper extends LiftRules.DispatchPF {
  import JsonAST._

  /**
   * Will the request accept a JSON response?  Yes if
   * the Accept header contains "text/json", "application/json" or
   * the Accept header is missing or contains "star/star" and the
   * suffix is "json".  Override this method to provide your
   * own logic.  If there's no suffix, no accepts (or it's "star/star")
   * then look to either the Content-Type header or the defaultGetAsJson
   * flag
   */
  protected def jsonResponse_?(in: Req): Boolean = {
    (in.acceptsJson_? && !in.acceptsStarStar) || 
    ((in.weightedAccept.isEmpty ||
      in.acceptsStarStar) && 
     (in.path.suffix.equalsIgnoreCase("json") ||
      in.json_? ||
      (in.path.suffix.length == 0 && defaultGetAsJson))) ||
    suplimentalJsonResponse_?(in)
  }

  /**
   * If the headers and the suffix say nothing about the
   * response type, should we default to JSON.  By default,
   * yes, override to change the behavior.
   */
  protected def defaultGetAsJson: Boolean = true

  /**
   * If the headers and the suffix say nothing about the
   * response type, should we default to XML.  By default,
   * no, override to change the behavior.
   */
  protected def defaultGetAsXml: Boolean = false

  /**
   * Take any value and convert it into a JValue.  Full box if
   * it works, empty if it does
   */
  protected def anyToJValue(in: Any): Box[JValue] = Helpers.tryo{
    implicit def formats = DefaultFormats
    Extraction.decompose(in)
  }
  
  /**
   * If there are additional custom rules (e.g., looking at query parameters)
   * you can override this method which is consulted if the other rules
   * in jsonResponse_? fail
   */
  protected def suplimentalJsonResponse_?(in: Req): Boolean = false
  
  /**
   * Will the request accept an XML response?  Yes if
   * the Accept header contains "application/xml" or "text/xml" or
   * the Accept header is missing or contains "star/star" and the
   * suffix is "xml".  Override this method to provide your
   * own logic.  If there's no suffix, no accepts (or it's "star/star")
   * then look to either the Content-Type header or the defaultGetAsXml
   * flag.
   */
  protected def xmlResponse_?(in: Req): Boolean = {
    (in.acceptsXml_? && !in.acceptsStarStar) || 
    ((in.weightedAccept.isEmpty ||
      in.acceptsStarStar) && 
     (in.path.suffix.equalsIgnoreCase("xml") ||
      in.xml_? ||
      (in.path.suffix.length == 0 && defaultGetAsXml))) ||
    suplimentalXmlResponse_?(in)
  }
  
  /**
   * If there are additional custom rules (e.g., looking at query parameters)
   * you can override this method which is consulted if the other rules
   * in xmlResponse_? fail
   */
  protected def suplimentalXmlResponse_?(in: Req): Boolean = false
  
  /**
   * A trait that defines the TestReq extractor.  Is
   * the request something that expects JSON, XML in the response.
   * Subclass this trait to change the behavior
   */
  protected trait TestReq {
    /**
     * Test to see if the request is expecting JSON, XML in the response.
     * The path and a Tuple2 representing RequestType and the Req
     * instance are extracted.
     */
    def unapply(r: Req): Option[(List[String], (RequestType, Req))] = 
      if (testResponse_?(r))
        Some(r.path.partPath -> (r.requestType -> r)) else None

    def testResponse_?(r: Req): Boolean
  }

  protected trait XmlTest {
    def testResponse_?(r: Req): Boolean = xmlResponse_?(r)
  }

  protected trait JsonTest {
    def testResponse_?(r: Req): Boolean = jsonResponse_?(r)
  }

  /**
   * The stable identifier for JsonReq.  You can use it
   * as an extractor.
   */
  protected lazy val JsonReq = new TestReq with JsonTest

  /**
   * The stable identifier for XmlReq.  You can use it
   * as an extractor.
   */
  protected lazy val XmlReq = new TestReq with XmlTest
  

  /**
   * A trait that defines the TestGet extractor.  Is
   * the request a GET and something that expects JSON or XML in the response.
   * Subclass this trait to change the behavior
   */
  protected trait TestGet {
    /**
     * Test to see if the request is a GET and expecting JSON in the response.
     * The path and the Req instance are extracted.
     */
    def unapply(r: Req): Option[(List[String], Req)] = 
      if (r.get_? && testResponse_?(r))
        Some(r.path.partPath -> r) else None


    def testResponse_?(r: Req): Boolean
  }

  /**
   * The stable identifier for JsonGet.  You can use it
   * as an extractor.
   */
  protected lazy val JsonGet = new TestGet with JsonTest

  /**
   * The stable identifier for XmlGet.  You can use it
   * as an extractor.
   */
  protected lazy val XmlGet = new TestGet with XmlTest



  /**
   * A trait that defines the TestDelete extractor.  Is
   * the request a DELETE and something that expects
   * JSON or XML in the response.
   * Subclass this trait to change the behavior
   */
  protected trait TestDelete {
    /**
     * Test to see if the request is a DELETE and
     * expecting JSON or XML in the response.
     * The path and the Req instance are extracted.
     */
    def unapply(r: Req): Option[(List[String], Req)] = 
      if (r.requestType.delete_? && testResponse_?(r))
        Some(r.path.partPath -> r) else None


    def testResponse_?(r: Req): Boolean
  }

  /**
   * The stable identifier for JsonDelete.  You can use it
   * as an extractor.
   */
  protected lazy val JsonDelete = new TestDelete with JsonTest

  /**
   * The stable identifier for XmlDelete.  You can use it
   * as an extractor.
   */
  protected lazy val XmlDelete = new TestDelete with XmlTest

  /**
   * A trait that defines the TestPost extractor.  Is
   * the request a POST, has JSON or XML data in the post body
   * and something that expects JSON or XML in the response.
   * Subclass this trait to change the behavior
   */
  protected trait TestPost[T] {
    /**
     * Test to see if the request is a POST, has JSON data in the
     * body and expecting JSON in the response.
     * The path, JSON Data and the Req instance are extracted.
     */
    def unapply(r: Req): Option[(List[String], (T, Req))] = 
      if (r.post_? && testResponse_?(r))
        body(r).toOption.map(t => (r.path.partPath -> (t -> r))) 
      else None

    
    def testResponse_?(r: Req): Boolean

    def body(r: Req): Box[T]
  }


  /**
    * A trait that defines the TestPatch extractor.  Is
    * the request a PATCH, has JSON or XML data in the post body
    * and something that expects JSON or XML in the response.
    * Subclass this trait to change the behavior
    */
  protected trait TestPatch[T] {
    /**
      * Test to see if the request is a PATCH, has JSON data in the
      * body and expecting JSON in the response.
      * The path, JSON Data and the Req instance are extracted.
      */
    def unapply(r: Req): Option[(List[String], (T, Req))] =
      if (r.patch_? && testResponse_?(r))
        body(r).toOption.map(t => (r.path.partPath -> (t -> r)))
      else None


    def testResponse_?(r: Req): Boolean

    def body(r: Req): Box[T]
  }

  /**
    * The stable identifier for JsonPatch.  You can use it
    * as an extractor.
    */
  protected lazy val JsonPatch = new TestPatch[JValue] with JsonTest with JsonBody

  /**
    * The stable identifier for XmlPatch.  You can use it
    * as an extractor.
    */
  protected lazy val XmlPatch = new TestPatch[Elem] with XmlTest with XmlBody


  /**
   * a trait that extracts the JSON body from a request  It is
   * composed with a TestXXX to get the correct thing for the extractor
   */
  protected trait JsonBody {
    def body(r: Req): Box[JValue] = r.json
  }

  /**
   * a trait that extracts the XML body from a request  It is
   * composed with a TestXXX to get the correct thing for the extractor
   */
  protected trait XmlBody {
    def body(r: Req): Box[Elem] = r.xml
  }

  /**
   * An extractor that tests the request to see if it's a GET and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Get req => ...</pre><br/>
   * or<br/>
   * <pre>case Get("api" :: id :: _, req) => ...</pre><br/>   * 
   */
  protected object Get {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.get_?) Some(r.path.partPath -> r) else None
                                
  }

  /**
   * An extractor that tests the request to see if it's a POST and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Post req => ...</pre><br/>
   * or<br/>
   * <pre>case Post("api" :: id :: _, req) => ...</pre><br/>
   */
  protected object Post {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.post_?) Some(r.path.partPath -> r) else None
                                
  }

  /**
   * An extractor that tests the request to see if it's a PUT and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Put req => ...</pre><br/>
   * or<br/>
   * <pre>case Put("api" :: id :: _, req) => ...</pre><br/>
   */
  protected object Put {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.put_?) Some(r.path.partPath -> r) else None
                                
  }

  /**
   * An extractor that tests the request to see if it's a PATCH and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Patch req => ...</pre><br/>
   * or<br/>
   * <pre>case Patch("api" :: id :: _, req) => ...</pre><br/>
   */
  protected object Patch {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.patch_?) Some(r.path.partPath -> r) else None

  }

  /**
   * An extractor that tests the request to see if it's a DELETE and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Delete req => ...</pre><br/>
   * or<br/>
   * <pre>case Delete("api" :: id :: _, req) => ...</pre><br/>
   */
  protected object Delete {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.requestType.delete_?) Some(r.path.partPath -> r) else None
                                
  }

  /**
   * An extractor that tests the request to see if it's an OPTIONS and
   * if it is, the path and the request are extracted.  It can
   * be used as:<br/>
   * <pre>case "api" :: id :: _ Options req => ...</pre><br/>
   * or<br/>
   * <pre>case Options("api" :: id :: _, req) => ...</pre><br/>   *
   */
  protected object Options {
    def unapply(r: Req): Option[(List[String], Req)] =
      if (r.requestType.options_?) Some(r.path.partPath -> r) else None

  }

  /**
   * A function that chooses JSON or XML based on the request..
   * Use with serveType
   */
  implicit def jxSel(req: Req): BoxOrRaw[JsonXmlSelect] = 
    if (jsonResponse_?(req)) JsonSelect
    else if (xmlResponse_?(req)) XmlSelect
    else None

  /**
   * Serve a given request by determining the request type, computing
   * the response and then converting the response to the given
   * type (e.g., JSON or XML).<br/><br/>
   * @param selection -- a function that determines the response type
   * based on the Req.
   * @param pf -- a PartialFunction that converts the request to a
   * response type (e.g., a case class that contains the response).
   * @param cvt -- a function that converts from the response type
   * to a the appropriate LiftResponse based on the selected response
   * type.
   */
  protected def serveType[T, SelectType](selection: Req => BoxOrRaw[SelectType])
  (pf: PartialFunction[Req, BoxOrRaw[T]])
  (implicit cvt: PartialFunction[(SelectType, T, Req), LiftResponse]): Unit = {
    serve(new PartialFunction[Req, () => Box[LiftResponse]] {
      def isDefinedAt(r: Req): Boolean = 
        selection(r).isDefined && pf.isDefinedAt(r)
   
      def apply(r: Req): () => Box[LiftResponse] = 
        () => {
          pf(r).box match {
            case Full(resp) =>
              val selType = selection(r).openOrThrowException("Full because pass isDefinedAt")
              if (cvt.isDefinedAt((selType, resp, r)))
                  Full(cvt((selType, resp, r)))
              else emptyToResp(ParamFailure("Unabled to convert the message", 
                                            Empty, Empty, 500))

            case e: EmptyBox => emptyToResp(e)
          }
        }
    }
    )
  }

  /**
   * Serve a request returning either JSON or XML.
   *
   * @param pf -- a Partial Function that converts the request into
   * an intermediate response.
   * @param cvt -- convert the intermediate response to a LiftResponse
   * based on the request being for XML or JSON.  If T is JsonXmlAble,
   * there are built-in converters.  Further, you can return auto(thing)
   * and that will invoke built-in converters as well.  The built-in
   * converters use Lift JSON's Extraction.decompose to convert the object
   * into JSON and then Xml.toXml() to convert to XML.
   */
  protected def serveJx[T](pf: PartialFunction[Req, BoxOrRaw[T]])
  (implicit cvt: JxCvtPF[T]): Unit =
    serveType(jxSel)(pf)(cvt)

  protected type JxCvtPF[T] = 
    PartialFunction[(JsonXmlSelect, T, Req), LiftResponse]

  /**
   * Serve a request returning either JSON or XML.
   *
   * @param pf -- a Partial Function that converts the request into
   * Any (note that the response must be convertable into
   * JSON vis Lift JSON Extraction.decompose
   */
  protected def serveJxa(pf: PartialFunction[Req, BoxOrRaw[Any]]): Unit = 
    serveType(jxSel)(pf)(new PartialFunction[(JsonXmlSelect,
                                              Any, Req), LiftResponse] {
      def isDefinedAt(p: (JsonXmlSelect, Any, Req)) =
        convertAutoJsonXmlAble.isDefinedAt((p._1, AutoJsonXmlAble(p._2), p._3))
      
      def apply(p: (JsonXmlSelect, Any, Req)) =
        convertAutoJsonXmlAble.apply((p._1, AutoJsonXmlAble(p._2), p._3))
    })

  /**
   * Return the implicit Formats instance for JSON conversion
   */
  protected implicit def formats: Formats = net.liftweb.json.DefaultFormats

  /**
   * The default way to convert a JsonXmlAble into JSON or XML
   */
  protected implicit lazy val convertJsonXmlAble: 
  PartialFunction[(JsonXmlSelect, JsonXmlAble, Req), LiftResponse] = {
    case (JsonSelect, obj, _) => Extraction.decompose(obj)

    case (XmlSelect, obj, _) => 
      Xml.toXml(Extraction.decompose(obj)).toList match {
        case x :: _ => x
        case _ => Text("")
      }
  }

  /**
   * The class that wraps anything for auto conversion to JSON or XML
   */
  protected final case class AutoJsonXmlAble(obj: Any)

  /**
   * wrap anything for autoconversion to JSON or XML
   */
  protected def auto(in: Any): Box[AutoJsonXmlAble] = 
    Full(new AutoJsonXmlAble(in))

  /**
   * Wrap a Box of anything for autoconversion to JSON or XML
   */
  protected def auto(in: Box[Any]): Box[AutoJsonXmlAble] =
    in.map(obj => new AutoJsonXmlAble(obj))

  /**
   * An implicit conversion that converts AutoJsonXmlAble into
   * JSON or XML
   */
  protected implicit lazy val convertAutoJsonXmlAble: 
  PartialFunction[(JsonXmlSelect, AutoJsonXmlAble, Req), LiftResponse] = {
    case (JsonSelect, AutoJsonXmlAble(obj), _) => 
      Extraction.decompose(obj)
    case (XmlSelect, AutoJsonXmlAble(obj), _) => 
      Xml.toXml(Extraction.decompose(obj)).toList match {
        case x :: _ => x
        case _ => Text("")
      }
  }

  /**
   * The stable identifier for JsonPost.  You can use it
   * as an extractor.
   */
  protected lazy val JsonPost = new TestPost[JValue] with JsonTest with JsonBody

  /**
   * The stable identifier for XmlPost.  You can use it
   * as an extractor.
   */
  protected lazy val XmlPost = new TestPost[Elem] with XmlTest with XmlBody

  /**
   * A trait that defines the TestPut extractor.  Is
   * the request a PUT, has JSON or XML data in the put body
   * and something that expects JSON or XML in the response.
   * Subclass this trait to change the behavior
   */
  protected trait TestPut[T] {
    /**
     * Test to see if the request is a PUT, has JSON or XML data in the
     * body and expecting JSON or XML in the response.
     * The path, Data and the Req instance are extracted.
     */
    def unapply(r: Req): Option[(List[String], (T, Req))] = 
      if (r.put_? && testResponse_?(r))
        body(r).toOption.map(b => (r.path.partPath -> (b -> r))) else None

    
    def testResponse_?(r: Req): Boolean

    def body(r: Req): Box[T]
  }

  /**
   * The stable identifier for JsonPut.  You can use it
   * as an extractor.
   */
  protected lazy val JsonPut = new TestPut[JValue] with JsonTest with JsonBody

  /**
   * The stable identifier for XmlPut.  You can use it
   * as an extractor.
   */
  protected lazy val XmlPut = new TestPut[Elem] with XmlTest with XmlBody

  /**
   * Extract a Pair using the same syntax that you use to make a Pair
   */
  protected object -> {
    def unapply[A, B](s: (A, B)): Option[(A, B)] = Some(s._1 -> s._2)
  }

  @volatile private var _dispatch: List[LiftRules.DispatchPF] = Nil
  
  private lazy val nonDevDispatch = _dispatch.reverse

  private def dispatch: List[LiftRules.DispatchPF] = 
    if (Props.devMode) _dispatch.reverse else nonDevDispatch

  /**
   * Is the Rest helper defined for a given request
   */
  def isDefinedAt(in: Req) = dispatch.find(_.isDefinedAt(in)).isDefined

  /**
   * Apply the Rest helper
   */
  def apply(in: Req): () => Box[LiftResponse] = 
    dispatch.find(_.isDefinedAt(in)).get.apply(in)

  /**
   * Add request handlers
   */
  protected def serve(handler: PartialFunction[Req, () => Box[LiftResponse]]): 
  Unit = _dispatch ::= handler 
  
  /**
   * Turn T into the return type expected by DispatchPF as long
   * as we can convert T to a LiftResponse.
   */
  protected implicit def thingToResp[T](in: T)(implicit c: T => LiftResponse):
  () => Box[LiftResponse] = () => Full(c(in))


  /**
   * If we're returning a future, then automatically turn the request into an Async request
   * @param in the LAFuture of the response type
   * @param c the implicit conversion from T to LiftResponse
   * @tparam T the type
   * @return Nothing
   */
  protected implicit def asyncToResponse[AsyncResolvableType, T](
    asyncContainer: AsyncResolvableType
  )(
    implicit asyncResolveProvider: CanResolveAsync[AsyncResolvableType, T],
             responseCreator: T => LiftResponse
  ): () => Box[LiftResponse] = () => {
    RestContinuation.async(reply => {
      asyncResolveProvider.resolveAsync(
        asyncContainer,
        { resolved => reply(responseCreator(resolved)) }
      )
    })
  }

  /**
   * If we're returning a future, then automatically turn the request into an Async request
   * @param in the LAFuture of the response type
   * @param c the implicit conversion from T to LiftResponse
   * @tparam T the type
   * @return Nothing
   */
  protected implicit def asyncBoxToResponse[AsyncResolvableType, T](
    asyncBoxContainer: AsyncResolvableType
  )(
    implicit asyncResolveProvider: CanResolveAsync[AsyncResolvableType, Box[T]],
             responseCreator: T => LiftResponse
  ): () => Box[LiftResponse] = () => {
    RestContinuation.async(reply => {
      asyncResolveProvider.resolveAsync(
        asyncBoxContainer,
        { resolvedBox => boxToResp(resolvedBox).apply() openOr NotFoundResponse() }
      )
    })
  }

  /**
   * Turn a Box[T] into the return type expected by
   * DispatchPF.  Note that this method will return
   * messages from Failure() and return codes and messages
   * from ParamFailure[Int[(msg, _, _, code) 
   */
  protected implicit def boxToResp[T](in: Box[T])
  (implicit c: T => LiftResponse): () => Box[LiftResponse] = 
    in match {
      case Full(v) => () => Full(c(v))
      case e: EmptyBox => () => emptyToResp(e)
    }

  protected def emptyToResp(eb: EmptyBox): Box[LiftResponse] =
    eb match {
      case ParamFailure(msg, _, _, code: Int) =>
        Full(InMemoryResponse(msg.getBytes("UTF-8"), 
                              ("Content-Type" ->
                               "text/plain; charset=utf-8") ::
                              Nil, Nil, code))
      
      case Failure(msg, _, _) => 
        Full(NotFoundResponse(msg))

      case _ => Empty
    }

  /**
   * Turn an Option[T] into the return type expected by
   * DispatchPF.
   */
  protected implicit def optionToResp[T](in: Option[T])
  (implicit c: T => LiftResponse): () => Box[LiftResponse] = 
    in match {
      case Some(v) => () => Full(c(v))
      case _ => () => Empty
    }

  /**
   * Turn a () => Box[T] into the return type expected by
   * DispatchPF.  Note that this method will return
   * messages from Failure() and return codes and messages
   * from ParamFailure[Int[(msg, _, _, code) 
   */
  protected implicit def boxFuncToResp[T](in: () => Box[T])
  (implicit c: T => LiftResponse): () => Box[LiftResponse] = 
    () => {
      in() match {
        case ParamFailure(msg, _, _, code: Int) =>
          Full(InMemoryResponse(msg.getBytes("UTF-8"), 
                                ("Content-Type" ->
                                 "text/plain; charset=utf-8") ::
                                Nil, Nil, code))
        
        case Failure(msg, _, _) => 
          Full(NotFoundResponse(msg))
        
        case Full(v) => Full(c(v))
        case _ => Empty
      }
    }
    
  /**
   * Turn an Option[T] into the return type expected by
   * DispatchPF.
   */
  protected implicit def optionFuncToResp[T](in: () => Option[T])
  (implicit c: T => LiftResponse): () => Box[LiftResponse] = 
    () => 
      in() match {
        case Some(v) => Full(c(v))
        case _ => Empty
      }


  /**
   * Override this method to create an AppXmlResponse with the
   * mime type application/xml rather then text/xml
   */
  protected def createXmlResponse(in: scala.xml.Node): LiftResponse =
    XmlResponse(in)

  /**
   * Convert a Node to an XmlResponse
   */
  protected implicit def nodeToResp(in: scala.xml.Node): LiftResponse = 
    createXmlResponse(in)

  /**
   * Convert a JValue to a LiftResponse
   */
  implicit def jsonToResp(in: JsonAST.JValue): LiftResponse = 
    JsonResponse(in)

  /**
   * Convert a JsExp to a LiftResponse
   */
  implicit def jsExpToResp(in: js.JsExp): LiftResponse = 
    JavaScriptResponse(in.cmd)

    /**
   * Convert a JsCmd to a LiftResponse
   */
  implicit def jsCmdToResp(in: js.JsCmd): LiftResponse =
    JavaScriptResponse(in)

  /** @return a SuperString with more available methods such as roboSplit or commafy */
  protected implicit def listStringToSuper(in: List[String]): 
  SuperListString = new SuperListString(in)

  /** @return a SuperString with more available methods such as roboSplit or commafy */
  protected implicit def stringToSuper(in: String): SuperString = new SuperString(in)

  /**
   * Allows you to use >> after a path list
   * to handle all the cases where you have a prefix
   * for a series of differ suffixes with the same
   * path prefix.  For example:
   * <code>
   * serve("foo" / "bar" >> {
   *   case baz :: Nil Post _ => ...
   *   case Nil Get _ => ...
   * })
   * </code>
   */
  protected implicit def listToServeMagic(in: List[String]): 
  ListServeMagic = new ListServeMagic(in)

  /**
   * Take an original piece of JSON (most probably, JObject
   * and replace all the JFields with those in toMerge
   */
  protected def mergeJson(original: JValue, toMerge: JValue): JValue = {
    def replace(lst: List[JField], f: JField): List[JField] = 
      f :: lst.filterNot(_.name == f.name)

    original match {
      case JObject(fields) => 
        toMerge match {
          case JObject(otherFields) =>
            JObject(otherFields.foldLeft(fields)(replace(_, _)))
          case _ => original
        }

      case _ => original // can't merge
    }
  }
}


/**
 * Do some magic to prefix path patterns with a single List
 */
final class ListServeMagic(list: List[String]) {
  val listLen = list.length

  /**
   * Used in conjunction with RestHelper.serveJx to
   * prefix the pattern matched path.  For example:
   * <code>
   * serveJx[Foo]("foo" / "bar" prefixJx {
   *   case FindBaz(baz) :: Nil Get _ => baz
   * })
   * </code>
   */
  def prefixJx[T](pf: PartialFunction[Req, BoxOrRaw[T]]): PartialFunction[Req, BoxOrRaw[T]] = 
    new PartialFunction[Req, BoxOrRaw[T]] {
      def isDefinedAt(req: Req): Boolean = 
        req.path.partPath.startsWith(list) && {
          pf.isDefinedAt(req.withNewPath(req.path.drop(listLen)))
        }

      def apply(req: Req): BoxOrRaw[T] = 
        pf.apply(req.withNewPath(req.path.drop(listLen)))
    }


  /**
   * Used in conjunction with RestHelper.serveJx to
   * prefix the pattern matched path.  For example:
   * <code>
   * serve("foo" / "bar" prefix {
   *   case FindBaz(baz) :: Nil GetJson _ => baz: JValue
   *   case FindBaz(baz) :: Nil GetXml _ => baz: Node
   * })
   * </code>
   */
  def prefix(pf: PartialFunction[Req, () => Box[LiftResponse]]):
  PartialFunction[Req, () => Box[LiftResponse]] =
    new PartialFunction[Req, () => Box[LiftResponse]] {
      def isDefinedAt(req: Req): Boolean = 
        req.path.partPath.startsWith(list) && {
          pf.isDefinedAt(req.withNewPath(req.path.drop(listLen)))
        }

      def apply(req: Req): () => Box[LiftResponse] = 
        pf.apply(req.withNewPath(req.path.drop(listLen)))
    }
 
}

/**
 * A trait that can be mixed into an class (probably a case class)
 * so that the class can be converted automatically into JSON or XML
 */
trait JsonXmlAble

/**
 * This trait is part of the ADT that allows the choice between 
 */
sealed trait JsonXmlSelect

/**
 * The Type for JSON
 */
final case object JsonSelect extends JsonXmlSelect

/**
 * The type for XML
 */
final case object XmlSelect extends JsonXmlSelect