--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Simoleon/Helpers/FavouriteButton.swift	Mon Jul 19 19:27:12 2021 +0100
@@ -0,0 +1,86 @@
+//
+//  FavouriteButton.swift
+//  Simoleon
+//
+//  Created by Dennis Concepción Martín on 19/07/2021.
+//
+
+import SwiftUI
+
+struct FavouriteButton: View {
+    var currencyPair: String
+    @Environment(\.managedObjectContext) private var viewContext
+    @FetchRequest(sortDescriptors: []) private var favourite: FetchedResults<Favourite>
+    
+    var body: some View {
+        Button(action: {
+            if isFavourite() {
+                removeFromFavourites()
+            } else {
+                addToFavourites()
+            }
+        }) {
+            RoundedRectangle(cornerRadius: 25)
+                .foregroundColor(Color(.secondarySystemBackground))
+                .frame(width: 75, height: 75)
+                .overlay(
+                    Image(systemName: generateStar())
+                        .font(.system(size: 28))
+                        .foregroundColor(Color(.systemYellow))
+                        
+                )
+        }
+    }
+    
+    private func isFavourite() -> Bool {
+        let favouriteCurrencyPairs = favourite.map { $0.currencyPair }
+        
+        if favouriteCurrencyPairs.contains(currencyPair) {
+            return true
+        } else {
+            return false
+        }
+    }
+    
+    private func generateStar() -> String {
+        if isFavourite() {
+            return "star.fill"
+        } else {
+            return "star"
+        }
+    }
+    
+    private func removeFromFavourites() {
+        withAnimation {
+            let favouriteObject = favourite.first(where: { $0.currencyPair == currencyPair })
+            viewContext.delete(favouriteObject ?? Favourite())
+            
+            do {
+                try viewContext.save()
+            } catch {
+                let nsError = error as NSError
+                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
+            }
+        }
+    }
+    
+    private func addToFavourites() {
+        withAnimation {
+            let favourite = Favourite(context: viewContext)
+            favourite.currencyPair = currencyPair
+            
+            do {
+                try viewContext.save()
+            } catch {
+                let nsError = error as NSError
+                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
+            }
+        }
+    }
+}
+
+struct FavouriteButton_Previews: PreviewProvider {
+    static var previews: some View {
+        FavouriteButton(currencyPair: "USD/GBP")
+    }
+}