Plan for refactoring WebCommands

HandlerPipeline.scala

// Change DefaultHttpRequestHandler to take a pipeline

class DefaultHttpRequestHandler(
    pipeline: Seq[Handler],
    router: Router,
    errorHandler: HttpErrorHandler,
    configuration: HttpConfiguration,
    filters: Seq[EssentialFilter]) extends HttpRequestHandler {
  ...
}

// Introduce a new type of Handler so it can be used in a pipeline

trait Handler
// Just a strawman interface - will definitely not look like this!
trait HandlerFunction {
  def handle(rh: RequestHeader): (RequesthHeader, Handler) 
}

// The following classes make up the default pipeline

// Move this out of Server class - this is what adds cookies, request ids, etc to
// all requests
class AddRequestAttributesHandler(requestFactory: RequestFactory) extends HandlerFunction {
  def handle(rh: RequestHeader, next: Handler): (RequestHeader, Handler) = {
    (requestFactory.copyRequestHeader(rh), next)
  }
}

// Move this out of our *ModelConversion classes
class ForwardedHeaderHandler(configuration: ForwardedHeaderHandlerConfig) extends HandlerFunction {
  def handle(rh: RequestHeader, next: Handler): (RequestHeader, Handler) = {
    val newConnection: RemoteConnection = forwardedConnect(rh.connection, rh.headers)
    (rh.withConnection(newConnection), next)
  }
}

// We can use this for backwards-compatibility with WebCommands
// but then deprecate WebCommands - Evolutions can just make its
// own Handler and run in the handler pipeline
class WebCommandsHandler(webCommands: WebCommands, optDevContext: Option[DevContext]) extends HandlerFunction {
  def handle(rh: RequestHeader, next: Handler): (RequestHeader, Handler) = {
    val optResult: Option[Result] = optDevContext.flatMap { devContext =>
      webCommands.handleWebCommand(request: RequestHeader, buildLink: BuildLink, path: File): Option[Result]
    }
    optResult.fold((rh, next)) { (rh, result => Action { result }) }
  }
}

// Fun question - could Router be run inside a Handler too? :)