--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Simoleon/Helpers/FavoriteButton.swift	Tue Jul 27 09:44:51 2021 +0100
@@ -0,0 +1,103 @@
+//
+//  FavoriteButton.swift
+//  Simoleon
+//
+//  Created by Dennis Concepción Martín on 19/07/2021.
+//
+
+import SwiftUI
+
+struct FavoriteButton: View {
+    var currencyPair: String
+    
+    @Environment(\.managedObjectContext) private var viewContext
+    @FetchRequest(sortDescriptors: []) private var favorite: FetchedResults<Favorite>
+    
+    @State private var starSymbol = "star"
+    
+    var body: some View {
+        let favoriteCurrencyPairs = favorite.map { $0.currencyPair }
+        Button(action: { favoriteAction(favoriteCurrencyPairs) }) {
+            RoundedRectangle(cornerRadius: 15)
+                .foregroundColor(Color(.secondarySystemBackground))
+                .frame(width: 60, height: 60)
+                .overlay(
+                    Image(systemName: generateStar(favoriteCurrencyPairs))
+                        .font(.system(size: 28))
+                        .foregroundColor(Color(.systemYellow))
+                )
+        }
+    }
+    
+    /*
+     If currency pair is favorite:
+     * Button action is to remove from favorites
+     else:
+     * Button action is to add to favorites
+     */
+    private func favoriteAction(_ favoriteCurrencyPairs: [String]) {
+        if favoriteCurrencyPairs.contains(currencyPair) {
+            removeFromFavorites()
+        } else {
+            addToFavorites()
+        }
+        
+        simpleSuccess()
+    }
+    
+    /*
+     if currency pair is favorite:
+     * Return "star.fill" symbol
+     else:
+     * Return "star"
+     */
+    private func generateStar(_ favoriteCurrencyPairs: [String]) -> String {
+        if favoriteCurrencyPairs.contains(currencyPair) {
+            return "star.fill"
+        } else {
+            return "star"
+        }
+    }
+    
+    /*
+     * Get first favorite core data object that matches the specified currency pair
+     * Delete it
+     */
+    private func removeFromFavorites() {
+        withAnimation {
+            let favoriteObject = favorite.first(where: { $0.currencyPair == currencyPair })
+            viewContext.delete(favoriteObject ?? Favorite())
+            
+            do {
+                try viewContext.save()
+            } catch {
+                let nsError = error as NSError
+                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
+            }
+        }
+    }
+    
+    /*
+     * Create a favorite core data object
+     * Save it
+     */
+    private func addToFavorites() {
+        withAnimation {
+            let favorite = Favorite(context: viewContext)
+            favorite.currencyPair = currencyPair
+            
+            do {
+                try viewContext.save()
+            } catch {
+                let nsError = error as NSError
+                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
+            }
+        }
+    }
+}
+
+struct FavoriteButton_Previews: PreviewProvider {
+    static var previews: some View {
+        FavoriteButton(currencyPair: "USD/GBP")
+    }
+}