From fa7a280f0e6e0bbf5f694de81eeeabb9db24c348 Mon Sep 17 00:00:00 2001
From: Wojciech Nagrodzki <278594+wnagrodzki@users.noreply.github.com>
Date: Thu, 3 Jun 2021 20:08:38 +0200
Subject: [PATCH] Suppress setting the same value on object

---
 .../UserInterfaceVariations/UIVariation.swift | 19 ++++++++++++----
 .../UIVariationTests.swift                    | 22 +++++++++++++++++++
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/Sources/UserInterfaceVariations/UIVariation.swift b/Sources/UserInterfaceVariations/UIVariation.swift
index b5050d0..fbc3e3a 100644
--- a/Sources/UserInterfaceVariations/UIVariation.swift
+++ b/Sources/UserInterfaceVariations/UIVariation.swift
@@ -63,17 +63,28 @@ public class UIVariation<Object: AnyObject, Value>: NSObject {
 extension UIVariation: UIVariationApplying {
     
     func applyIfMatchesTraitEnvironment() {
+        guard doesMatchTraitEnvironment() else { return }
+        object[keyPath: property] = value
+    }
+    
+    func applyIfMatchesTraitEnvironment() where Value: Equatable {
+        guard doesMatchTraitEnvironment() else { return }
+        guard object[keyPath: property] != value else { return }
+        object[keyPath: property] = value
+    }
+    
+    private func doesMatchTraitEnvironment() -> Bool {
         guard let traitCollection = traitEnvironment?.traitCollection else {
             print("Missing traitEnvironment when trying to apply \(self)")
-            return
+            return false
         }
         if let horizontalSizeClass = horizontalSizeClass {
-            if traitCollection.horizontalSizeClass != horizontalSizeClass { return }
+            if traitCollection.horizontalSizeClass != horizontalSizeClass { return false }
         }
         if let verticalSizeClass = verticalSizeClass {
-            if traitCollection.verticalSizeClass != verticalSizeClass { return }
+            if traitCollection.verticalSizeClass != verticalSizeClass { return false }
         }
-        object[keyPath: property] = value
+        return true
     }
 }
 
diff --git a/Tests/UserInterfaceVariationsTests/UIVariationTests.swift b/Tests/UserInterfaceVariationsTests/UIVariationTests.swift
index c4bcd2d..4061d20 100644
--- a/Tests/UserInterfaceVariationsTests/UIVariationTests.swift
+++ b/Tests/UserInterfaceVariationsTests/UIVariationTests.swift
@@ -85,6 +85,20 @@ final class UIVariationTests: XCTestCase {
         XCTAssertNotEqual(label.text, sut.value)
     }
     
+    func test_When_object_value_is_already_equal_to_variation_value_Then_variation_is_NOT_applied() {
+        let object = Object()
+        let sut = UIVariation(object: object,
+                              keyPath: \.text,
+                              value: valueWhenCompact,
+                              horizontalSizeClass: .compact,
+                              verticalSizeClass: nil)
+        traitEnvironment.traitCollection = UITraitCollection(horizontalSizeClass: .compact)
+        sut.traitEnvironment = traitEnvironment
+        sut.applyIfMatchesTraitEnvironment()
+        sut.applyIfMatchesTraitEnvironment()
+        XCTAssertEqual(object.setCount, 1)
+    }
+    
     func test_factory_method_for_sizeClassDimension_horizontal() {
         let variations = UIVariation.make(for: label,
                                           property: \.text,
@@ -134,3 +148,11 @@ class TraitEnvironmentStub: NSObject, UITraitEnvironment {
         
     }
 }
+
+class Object {
+    
+    var text: String? {
+        didSet { setCount += 1 }
+    }
+    var setCount = 0
+}