1 files changed, 110 insertions, 0 deletions
diff --git a/src/main/scala/xyz/driver/common/utils/Computation.scala b/src/main/scala/xyz/driver/common/utils/Computation.scala
new file mode 100644
index 0000000..a435afe
--- /dev/null
+++ b/src/main/scala/xyz/driver/common/utils/Computation.scala
@@ -0,0 +1,110 @@
+package xyz.driver.common.utils
+
+import scala.concurrent.{ExecutionContext, Future}
+
+/**
+  * Takes care of computations
+  *
+  * Success(either) - the computation will be continued.
+  * Failure(error) - the computation was failed with unhandled error.
+  *
+  * Either[Result, T]:
+  * Left(result) is a final and handled result, another computations (map, flatMap) will be ignored.
+  * Right(T) is a current result. Functions in map/flatMap will continue the computation.
+  *
+  * Example:
+  * {{{
+  * import scala.concurrent.ExecutionContext.Implicits.global
+  * import scala.concurrent.{ExecutionContext, Future}
+  * import com.drivergrp.server.com.drivergrp.server.common.utils.Computation
+  *
+  * def successful = for {
+  *   x <- Computation.continue(1)
+  *   y <- Computation.continue(2)
+  * } yield s"\$x + \$y"
+  *
+  * // Prints "Success(1 + 2)"
+  * successful.join.onComplete(print)
+  *
+  * def failed = for {
+  *   x <- Computation.abort("Failed on x")
+  *   _ = print("Second step")
+  *   y <- Computation.continue(2)
+  * } yield s"\$x + \$y"
+  *
+  * // Prints "Success(Failed on x)"
+  * failed.join.onComplete(print)
+  * }}}
+  *
+  * TODO: Make future private
+  *
+  * @param future The final flow in a future.
+  * @tparam R Type of result for aborted computation.
+  * @tparam T Type of result for continued computation.
+  */
+final case class Computation[+R, +T](future: Future[Either[R, T]]) {
+
+  def flatMap[R2, T2](f: T => Computation[R2, T2])(implicit ec: ExecutionContext, ev: R <:< R2): Computation[R2, T2] = {
+    Computation(future.flatMap {
+      case Left(x) => Future.successful(Left(x))
+      case Right(x) => f(x).future
+    })
+  }
+
+  def processExceptions[R2](f: PartialFunction[Throwable, R2])
+                           (implicit ev1: R <:< R2,
+                            ec: ExecutionContext): Computation[R2, T] = {
+    val strategy = f.andThen(x => Left(x): Either[R2, T])
+    val castedFuture: Future[Either[R2, T]] = future.map {
+      case Left(x) => Left(x)
+      case Right(x) => Right(x)
+    }
+    Computation(castedFuture.recover(strategy))
+  }
+
+  def map[T2](f: T => T2)(implicit ec: ExecutionContext): Computation[R, T2] = flatMap { a =>
+    Computation.continue(f(a))
+  }
+
+  def andThen(f: T => Any)(implicit ec: ExecutionContext): Computation[R, T] = map { a =>
+    f(a)
+    a
+  }
+
+  def filter(f: T => Boolean)(implicit ec: ExecutionContext): Computation[R, T] = map { a =>
+    if (f(a)) a
+    else throw new NoSuchElementException("When filtering")
+  }
+
+  def withFilter(f: T => Boolean)(implicit ec: ExecutionContext): Computation[R, T] = filter(f)
+
+  def foreach[T2](f: T => T2)(implicit ec: ExecutionContext): Unit = future.foreach {
+    case Right(x) => f(x)
+    case _ =>
+  }
+
+  def toFuture[R2](resultFormatter: T => R2)(implicit ec: ExecutionContext, ev: R <:< R2): Future[R2] = future.map {
+    case Left(x) => x
+    case Right(x) => resultFormatter(x)
+  }
+
+  def toFuture[R2](implicit ec: ExecutionContext, ev1: R <:< R2, ev2: T <:< R2): Future[R2] = future.map {
+    case Left(x) => x
+    case Right(x) => x
+  }
+
+}
+
+object Computation {
+
+  def continue[T](x: T): Computation[Nothing, T] = Computation(Future.successful(Right(x)))
+
+  def abort[R](result: R): Computation[R, Nothing] = Computation(Future.successful(Left(result)))
+
+  def fail(exception: Throwable): Computation[Nothing, Nothing] = Computation(Future.failed(exception))
+
+  def fromFuture[T](input: Future[T])(implicit ec: ExecutionContext): Computation[Nothing, T] = Computation {
+    input.map { x => Right(x) }
+  }
+
+}