From a7576f548bda7452c46cdaea6fa75216f92e3a8d Mon Sep 17 00:00:00 2001
From: Dmitry Kurinskiy <name.alari@gmail.com>
Date: Sat, 10 Mar 2018 15:50:45 +0100
Subject: [PATCH] Functor and Contravariant typeclasses for CryptoHasher (#80)

---
 .../fluence/crypto/hash/JsCryptoHasher.scala  | 25 ++++--------
 .../fluence/crypto/hash/CryptoHasher.scala    | 40 +++++++++++++++++++
 2 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/js/src/main/scala/fluence/crypto/hash/JsCryptoHasher.scala b/js/src/main/scala/fluence/crypto/hash/JsCryptoHasher.scala
index 7a8d880..c7f95e6 100644
--- a/js/src/main/scala/fluence/crypto/hash/JsCryptoHasher.scala
+++ b/js/src/main/scala/fluence/crypto/hash/JsCryptoHasher.scala
@@ -24,26 +24,17 @@ import scala.scalajs.js.JSConverters._
 
 object JsCryptoHasher {
 
-  lazy val Sha256: CryptoHasher.Bytes = new CryptoHasher[Array[Byte], Array[Byte]] {
-    override def hash(msg1: Array[Byte]): Array[Byte] = {
+  lazy val Sha256: CryptoHasher.Bytes =
+    CryptoHasher.buildM[Array[Byte], Array[Byte]]{ msg ⇒
       val sha256 = new SHA256()
-      sha256.update(msg1.toJSArray)
+      sha256.update(msg.toJSArray)
       ByteVector.fromValidHex(sha256.digest("hex")).toArray
-    }
-    override def hash(msg1: Array[Byte], msg2: Array[Byte]*): Array[Byte] = {
-      hash(msg1 ++ msg2.flatten)
-    }
-  }
+    }(_ ++ _)
 
-  lazy val Sha1: CryptoHasher.Bytes = new CryptoHasher[Array[Byte], Array[Byte]] {
-    override def hash(msg1: Array[Byte]): Array[Byte] = {
+  lazy val Sha1: CryptoHasher.Bytes =
+    CryptoHasher.buildM[Array[Byte], Array[Byte]]{ msg ⇒
       val sha1 = new SHA1()
-      sha1.update(msg1.toJSArray)
+      sha1.update(msg.toJSArray)
       ByteVector.fromValidHex(sha1.digest("hex")).toArray
-    }
-    override def hash(msg1: Array[Byte], msg2: Array[Byte]*): Array[Byte] = {
-      hash(msg1 ++ msg2.flatten)
-    }
-
-  }
+    }(_ ++ _)
 }
diff --git a/src/main/scala/fluence/crypto/hash/CryptoHasher.scala b/src/main/scala/fluence/crypto/hash/CryptoHasher.scala
index 8e0eac9..75ea307 100644
--- a/src/main/scala/fluence/crypto/hash/CryptoHasher.scala
+++ b/src/main/scala/fluence/crypto/hash/CryptoHasher.scala
@@ -17,20 +17,60 @@
 
 package fluence.crypto.hash
 
+import cats.kernel.Semigroup
+import cats.{ Contravariant, Functor, Monoid, Traverse }
+
+import scala.language.{ higherKinds, reflectiveCalls }
+
 /**
  * TODO add F[_] effect
  * Base interface for hashing.
+ *
  * @tparam M type of message for hashing
  * @tparam H type of hashed message
  */
 trait CryptoHasher[M, H] {
+  self ⇒
 
   def hash(msg: M): H
 
   def hash(msg1: M, msgN: M*): H
 
+  def hashM[F[_] : Traverse](ms: F[M])(implicit M: Monoid[M]): H =
+    hash(Traverse[F].fold(ms))
+
+  final def map[B](f: H ⇒ B): CryptoHasher[M, B] = new CryptoHasher[M, B] {
+    override def hash(msg: M): B = f(self.hash(msg))
+
+    override def hash(msg1: M, msgN: M*): B = f(self.hash(msg1, msgN: _*))
+  }
+
+  final def contramap[N](f: N ⇒ M): CryptoHasher[N, H] = new CryptoHasher[N, H] {
+    override def hash(msg: N): H = self.hash(f(msg))
+
+    override def hash(msg1: N, msgN: N*): H = self.hash(f(msg1), msgN.map(f): _*)
+  }
+
 }
 
 object CryptoHasher {
   type Bytes = CryptoHasher[Array[Byte], Array[Byte]]
+
+  def buildM[M : Semigroup, H](h: M ⇒ H): CryptoHasher[M, H] = new CryptoHasher[M, H] {
+    override def hash(msg: M): H = h(msg)
+
+    override def hash(msg1: M, msgN: M*): H = h(msgN.foldLeft(msg1)(Semigroup[M].combine))
+  }
+
+  implicit def cryptoHasherFunctor[M]: Functor[({ type λ[α] = CryptoHasher[M, α] })#λ] =
+    new Functor[({ type λ[α] = CryptoHasher[M, α] })#λ] {
+      override def map[A, B](fa: CryptoHasher[M, A])(f: A ⇒ B): CryptoHasher[M, B] =
+        fa.map(f)
+    }
+
+  implicit def cryptoHasherContravariant[H]: Contravariant[({ type λ[α] = CryptoHasher[α, H] })#λ] =
+    new Contravariant[({ type λ[α] = CryptoHasher[α, H] })#λ] {
+      override def contramap[A, B](fa: CryptoHasher[A, H])(f: B ⇒ A): CryptoHasher[B, H] =
+        fa.contramap(f)
+    }
 }