From c07f98349ac5dc646855d00425a9dc2c3324465e Mon Sep 17 00:00:00 2001
From: adamw <adam@warski.org>
Date: Thu, 3 Aug 2017 11:38:23 +0200
Subject: Making the response monad a top-level concept, to make it possible to
 write SttpHandler wrappers.

---
 .../sttp/HttpURLConnectionSttpHandler.scala        |  2 +
 .../scala/com/softwaremill/sttp/MonadError.scala   | 44 ++++++++++++++++++++++
 .../scala/com/softwaremill/sttp/SttpHandler.scala  |  5 +++
 3 files changed, 51 insertions(+)
 create mode 100644 core/src/main/scala/com/softwaremill/sttp/MonadError.scala

(limited to 'core')

diff --git a/core/src/main/scala/com/softwaremill/sttp/HttpURLConnectionSttpHandler.scala b/core/src/main/scala/com/softwaremill/sttp/HttpURLConnectionSttpHandler.scala
index 6c3368a..d5c2ccd 100644
--- a/core/src/main/scala/com/softwaremill/sttp/HttpURLConnectionSttpHandler.scala
+++ b/core/src/main/scala/com/softwaremill/sttp/HttpURLConnectionSttpHandler.scala
@@ -33,6 +33,8 @@ object HttpURLConnectionSttpHandler extends SttpHandler[Id, Nothing] {
     }
   }
 
+  override def responseMonad: MonadError[Id] = IdMonad
+
   private def setBody(body: RequestBody[Nothing], c: HttpURLConnection): Unit = {
     if (body != NoBody) c.setDoOutput(true)
 
diff --git a/core/src/main/scala/com/softwaremill/sttp/MonadError.scala b/core/src/main/scala/com/softwaremill/sttp/MonadError.scala
new file mode 100644
index 0000000..e5e7ab8
--- /dev/null
+++ b/core/src/main/scala/com/softwaremill/sttp/MonadError.scala
@@ -0,0 +1,44 @@
+package com.softwaremill.sttp
+
+import scala.concurrent.{ExecutionContext, Future, Promise}
+import scala.language.higherKinds
+
+trait MonadError[R[_]] {
+  def unit[T](t: T): R[T]
+  def map[T, T2](fa: R[T], f: T => T2): R[T2]
+  def flatMap[T, T2](fa: R[T], f: T => R[T2]): R[T2]
+  def error[T](t: Throwable): R[T]
+
+  def flatten[T](ffa: R[R[T]]): R[T] = flatMap[R[T], T](ffa, identity)
+}
+
+trait MonadAsyncError[R[_]] extends MonadError[R] {
+  def async[T](register: (Either[Throwable, T] => Unit) => Unit): R[T]
+}
+
+object IdMonad extends MonadError[Id] {
+  override def unit[T](t: T): Id[T] = t
+  override def map[T, T2](fa: Id[T], f: (T) => T2): Id[T2] = f(fa)
+  override def flatMap[T, T2](fa: Id[T], f: (T) => Id[T2]): Id[T2] = f(fa)
+  override def error[T](t: Throwable): Id[T] = throw t
+}
+
+class FutureMonad(implicit ec: ExecutionContext)
+    extends MonadAsyncError[Future] {
+
+  override def unit[T](t: T): Future[T] = Future.successful(t)
+  override def map[T, T2](fa: Future[T], f: (T) => T2): Future[T2] = fa.map(f)
+  override def flatMap[T, T2](fa: Future[T], f: (T) => Future[T2]): Future[T2] =
+    fa.flatMap(f)
+  override def error[T](t: Throwable): Future[T] = Future.failed(t)
+
+  override def async[T](
+      register: ((Either[Throwable, T]) => Unit) => Unit): Future[T] = {
+    val p = Promise[T]()
+    register {
+      case Left(t)  => p.failure(t)
+      case Right(t) => p.success(t)
+    }
+    p.future
+  }
+}
diff --git a/core/src/main/scala/com/softwaremill/sttp/SttpHandler.scala b/core/src/main/scala/com/softwaremill/sttp/SttpHandler.scala
index 800d66a..bdcc1b5 100644
--- a/core/src/main/scala/com/softwaremill/sttp/SttpHandler.scala
+++ b/core/src/main/scala/com/softwaremill/sttp/SttpHandler.scala
@@ -11,4 +11,9 @@ import scala.language.higherKinds
 trait SttpHandler[R[_], -S] {
   def send[T](request: Request[T, S]): R[Response[T]]
   def close(): Unit = {}
+  /**
+    * The monad in which the responses are wrapped. Allows writing wrapper
+    * handlers, which map/flatMap over the return value of [[send]].
+    */
+  def responseMonad: MonadError[R]
 }
-- 
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