Merge pull request #97 from barbasa/master

SCALA-49: Introduction to Optics with Monocole

Author: JonCook

build.sbt

@@ -44,3 +44,15 @@ lazy val scala_test = (project in file("scala-test"))
     libraryDependencies += "org.scalamock" %% "scalamock" % "4.4.0" % Test,
     libraryDependencies += "com.novocode" % "junit-interface" % "0.11" % "test"
   )
+
+val monocleVersion = "2.0.4"
+lazy val scala_libraries = (project in file("scala-libraries"))
+    .settings(
+      name := "scala-libraries",
+      libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.5" % Test,
+      libraryDependencies ++= Seq(
+        "com.github.julien-truffaut" %% "monocle-core" % monocleVersion,
+        "com.github.julien-truffaut" %% "monocle-macro" % monocleVersion,
+        "com.github.julien-truffaut" %% "monocle-law" % monocleVersion % "test"
+      )
+   )

scala-libraries/src/main/scala/com/baeldung/scala/monocle/OpticsExamples.scala

@@ -0,0 +1,79 @@
+package com.baeldung.scala.monocle
+
+import monocle.{Iso, Lens, Prism, Optional}
+import monocle.macros.GenLens
+import monocle.macros.Lenses
+
+object OpticsExamples {
+
+  trait Discount
+  case class NoDiscount() extends Discount
+  case class PercentageOff(value: Double) extends Discount
+  case class FixPriceOff(value: Double) extends Discount
+
+  case class User(name: String, cart: Cart)
+  case class Cart(id: String, item: Item, quantity: Int)
+
+  case class Item(
+    sku: String,
+    price: Double,
+    leftInStock: Int,
+    discount: Discount
+  )
+
+  def updateStockWithoutLenses(user: User): User = {
+    user.copy(
+      cart = user.cart.copy(
+        item = user.cart.item.copy(leftInStock = user.cart.item.leftInStock - 1)
+      )
+    )
+  }
+
+  def updateStockWithLenses(user: User): User = {
+
+    val cart: Lens[User, Cart] = GenLens[User](_.cart)
+    val item: Lens[Cart, Item] = GenLens[Cart](_.item)
+    val leftInStock: Lens[Item, Int] = GenLens[Item](_.leftInStock)
+
+    (cart composeLens item composeLens leftInStock).modify(_ - 1)(user)
+  }
+
+  def updateDiscountedItemsPrice(cart: Cart, newDiscount: Double): Cart = {
+    val discountLens: Lens[Item, Discount] = GenLens[Item](_.discount)
+    val onlyPctDiscount = Prism.partial[Discount, Double] {
+      case PercentageOff(p) => p
+    }(PercentageOff)
+
+    val newItem =
+      (discountLens composePrism onlyPctDiscount set newDiscount)(cart.item)
+
+    cart.copy(item = newItem)
+  }
+
+  def getDiscountValue(discount: Discount): Option[Double] = {
+    val maybeDiscountValue = Optional[Discount, Double] {
+      case pctOff: PercentageOff => Some(pctOff.value)
+      case fixOff: FixPriceOff   => Some(fixOff.value)
+      case _                     => None
+    } { discountValue => discount =>
+      discount match {
+        case pctOff: PercentageOff => pctOff.copy(value = discountValue)
+        case fixOff: FixPriceOff   => fixOff.copy(value = discountValue)
+        case _                     => discount
+      }
+    }
+
+    maybeDiscountValue.getOption(discount)
+
+  }
+
+  case class PriceEUR(value: Double)
+  case class PriceGBP(value: Double)
+
+  val tranformCurrency = Iso[PriceEUR, PriceGBP] { eur =>
+    PriceGBP(eur.value * 0.9)
+  } { gbp =>
+    PriceEUR(gbp.value / 0.9)
+  }
+
+}

scala-libraries/src/test/scala/com/baeldung/scala/monocle/OpticsExamplesUnitTest.scala

@@ -0,0 +1,65 @@
+package com.baeldung.scala.monocle
+
+import org.scalatest._
+import org.scalatest.Assertions._
+import scala.util.{Success, Failure}
+import OpticsExamples._
+
+class OpticsExamplesUnitTest extends FlatSpec with Matchers {
+
+  "OpticExamples" should "update stock without Lenses" in {
+    val currentStock = 10
+    val item = Item("123sku", 35L, currentStock, NoDiscount())
+    val cart = Cart("abc123", item, 1)
+    val user = User("joe", cart)
+
+    val newUser = updateStockWithoutLenses(user)
+    assert(newUser.cart.item.leftInStock == currentStock - 1)
+  }
+
+  it should "update stock with Lenses" in {
+    val currentStock = 10
+    val item = Item("123sku", 35L, currentStock, NoDiscount())
+    val cart = Cart("abc123", item, 1)
+    val user = User("joe", cart)
+
+    val newUser = updateStockWithLenses(user)
+    assert(newUser.cart.item.leftInStock == currentStock - 1)
+  }
+
+  it should "update discount percentage values" in {
+    val originalDiscount = 10L
+    val newDiscount = 5L
+    val updatedCart = updateDiscountedItemsPrice(
+      Cart("abc", Item("item123", 23L, 1, PercentageOff(originalDiscount)), 1),
+      newDiscount
+    )
+    assert(updatedCart.item.discount == PercentageOff(newDiscount))
+  }
+
+  it should "not update discount fix price values" in {
+    val originalDiscount = 10L
+    val newDiscount = 5L
+    val updatedCart = updateDiscountedItemsPrice(
+      Cart("abc", Item("item123", 23L, 1, FixPriceOff(originalDiscount)), 1),
+      newDiscount
+    )
+    assert(updatedCart.item.discount == FixPriceOff(originalDiscount))
+  }
+
+  it should "return the Fix Off discount value" in {
+    val value = 3L
+    assert(getDiscountValue(FixPriceOff(value)) == Some(value))
+  }
+
+  it should "return no discount value" in {
+    assert(getDiscountValue(NoDiscount()) == None)
+  }
+
+  it should "transform GBP to EUR correctly" in {
+    val x =
+      tranformCurrency.modify(gbp => gbp.copy(gbp.value + 90L))(PriceEUR(1000L))
+    assert(x.value == 1100L)
+  }
+
+}