💾 Fix #3: Implement (local) persistence (#8)

## Content
💾 Fix #3: Implement (local) persistence
♻️ Implement DRY on weighted average calculation
🐛 Fix #6 : Prevent subjects from getting updated when user cancels editing

Reviewed-on: #8

Graduator/Graduator.xcodeproj/project.pbxproj

@@ -19,6 +19,9 @@
 		EC242B882A1FC605006FE760 /* NoGradesInfo.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC242B872A1FC605006FE760 /* NoGradesInfo.swift */; };
 		EC242B8A2A1FCECA006FE760 /* AverageBlockView.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC242B892A1FCECA006FE760 /* AverageBlockView.swift */; };
 		EC5FE5A52A20882F0028AA5F /* Formatters.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC5FE5A42A20882F0028AA5F /* Formatters.swift */; };
+		EC8BAD162A3465230062226B /* UnitsStore.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC8BAD152A3465230062226B /* UnitsStore.swift */; };
+		EC8BAD1A2A34BC170062226B /* WeightedGrade.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC8BAD192A34BC170062226B /* WeightedGrade.swift */; };
+		EC8BAD1C2A34BE4C0062226B /* WeightedAverageCalculator.swift in Sources */ = {isa = PBXBuildFile; fileRef = EC8BAD1B2A34BE4C0062226B /* WeightedAverageCalculator.swift */; };
 		ECB2FFCE2A23C4A700FF9F91 /* SubjectFormView.swift in Sources */ = {isa = PBXBuildFile; fileRef = ECB2FFCD2A23C4A700FF9F91 /* SubjectFormView.swift */; };
 		ECB2FFD02A23C4B700FF9F91 /* SubjectFormVM.swift in Sources */ = {isa = PBXBuildFile; fileRef = ECB2FFCF2A23C4B700FF9F91 /* SubjectFormVM.swift */; };
 		ECC581D22A1D085B006C55EF /* GraduatorApp.swift in Sources */ = {isa = PBXBuildFile; fileRef = ECC581D12A1D085B006C55EF /* GraduatorApp.swift */; };
@@ -41,6 +44,9 @@
 		EC242B872A1FC605006FE760 /* NoGradesInfo.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = NoGradesInfo.swift; sourceTree = "<group>"; };
 		EC242B892A1FCECA006FE760 /* AverageBlockView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AverageBlockView.swift; sourceTree = "<group>"; };
 		EC5FE5A42A20882F0028AA5F /* Formatters.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Formatters.swift; sourceTree = "<group>"; };
+		EC8BAD152A3465230062226B /* UnitsStore.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UnitsStore.swift; sourceTree = "<group>"; };
+		EC8BAD192A34BC170062226B /* WeightedGrade.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WeightedGrade.swift; sourceTree = "<group>"; };
+		EC8BAD1B2A34BE4C0062226B /* WeightedAverageCalculator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WeightedAverageCalculator.swift; sourceTree = "<group>"; };
 		ECB2FFCD2A23C4A700FF9F91 /* SubjectFormView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SubjectFormView.swift; sourceTree = "<group>"; };
 		ECB2FFCF2A23C4B700FF9F91 /* SubjectFormVM.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SubjectFormVM.swift; sourceTree = "<group>"; };
 		ECC581CE2A1D085B006C55EF /* Graduator.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = Graduator.app; sourceTree = BUILT_PRODUCTS_DIR; };
@@ -108,6 +114,14 @@
 			path = Utils;
 			sourceTree = "<group>";
 		};
+		EC8BAD142A34650D0062226B /* Data */ = {
+			isa = PBXGroup;
+			children = (
+				EC8BAD152A3465230062226B /* UnitsStore.swift */,
+			);
+			path = Data;
+			sourceTree = "<group>";
+		};
 		ECB2FFCC2A23C49500FF9F91 /* Forms */ = {
 			isa = PBXGroup;
 			children = (
@@ -135,12 +149,12 @@
 		ECC581D02A1D085B006C55EF /* Graduator */ = {
 			isa = PBXGroup;
 			children = (
+				EC8BAD142A34650D0062226B /* Data */,
 				ECE6E3C02A1F80F6004FE471 /* Model */,
 				ECC581DF2A1D08C3006C55EF /* ViewModel */,
 				EC242B6F2A1F8260006FE760 /* View */,
 				ECC581D12A1D085B006C55EF /* GraduatorApp.swift */,
 				EC242B702A1F8283006FE760 /* MainView.swift */,
-				EC242B822A1FAA9B006FE760 /* Stub.swift */,
 				ECC581D52A1D085C006C55EF /* Assets.xcassets */,
 				ECC581D72A1D085C006C55EF /* Preview Content */,
 			);
@@ -169,9 +183,12 @@
 		ECE6E3C02A1F80F6004FE471 /* Model */ = {
 			isa = PBXGroup;
 			children = (
+				EC242B822A1FAA9B006FE760 /* Stub.swift */,
 				EC242B6B2A1F81AE006FE760 /* Subject.swift */,
 				EC242B692A1F8189006FE760 /* Unit.swift */,
 				EC242B6D2A1F81CC006FE760 /* UnitsManager.swift */,
+				EC8BAD192A34BC170062226B /* WeightedGrade.swift */,
+				EC8BAD1B2A34BE4C0062226B /* WeightedAverageCalculator.swift */,
 			);
 			path = Model;
 			sourceTree = "<group>";
@@ -251,8 +268,11 @@
 				EC242B6E2A1F81CC006FE760 /* UnitsManager.swift in Sources */,
 				ECC581E52A1D0C44006C55EF /* UnitVM.swift in Sources */,
 				EC5FE5A52A20882F0028AA5F /* Formatters.swift in Sources */,
+				EC8BAD162A3465230062226B /* UnitsStore.swift in Sources */,
 				EC242B7F2A1F83BF006FE760 /* UnitsManagerVM.swift in Sources */,
 				EC242B7B2A1F838C006FE760 /* UnitViewCell.swift in Sources */,
+				EC8BAD1C2A34BE4C0062226B /* WeightedAverageCalculator.swift in Sources */,
+				EC8BAD1A2A34BC170062226B /* WeightedGrade.swift in Sources */,
 				EC242B6C2A1F81AE006FE760 /* Subject.swift in Sources */,
 				EC242B8A2A1FCECA006FE760 /* AverageBlockView.swift in Sources */,
 				ECB2FFD02A23C4B700FF9F91 /* SubjectFormVM.swift in Sources */,

Graduator/Graduator/Data/UnitsStore.swift

@@ -0,0 +1,48 @@
+//
+//  UnitsStore.swift
+//  Graduator
+//
+//  Created by etudiant on 2023-06-10.
+//
+
+import SwiftUI
+
+
+class UnitsStore: ObservableObject {
+        
+    private static func fileURL() throws -> URL {
+        try FileManager.default.url(
+            for: .documentDirectory,
+            in: .userDomainMask,
+            appropriateFor: nil,
+            create: false
+        ).appendingPathComponent("dat.data.tho")
+    }
+    
+    func load<T: Codable>(defaultValue: [T]) async throws -> [T] {
+            
+        let task = Task<[T], Error> {
+            let fileURL = try Self.fileURL()
+            let data = try? Data(contentsOf: fileURL)
+            var elements: [T] = defaultValue
+            if let validData = data, !validData.isEmpty {
+                elements = try JSONDecoder().decode([T].self, from: validData)
+            }
+            return elements
+        }
+        
+        return try await task.value
+    }
+    
+    func save<T: Codable>(elements: [T]) async throws {
+        
+        let task = Task {
+            let data = try JSONEncoder().encode(elements)
+            let outfile = try Self.fileURL()
+            try data.write(to: outfile)
+        }
+        
+        _ = try await task.value
+    }
+    
+}

Graduator/Graduator/GraduatorApp.swift

@@ -14,6 +14,13 @@ struct GraduatorApp: App {
     var body: some Scene {
         WindowGroup {
             MainView(unitsManagerVM: unitsManagerVM)
+                .task {
+                    do {
+                        try await unitsManagerVM.load()
+                    } catch {
+                        fatalError(error.localizedDescription)
+                    }
+                }
                 .environmentObject(unitsManagerVM)
         }
     }

Graduator/Graduator/Model/Stub.swift

@@ -121,7 +121,7 @@ struct Stub {
                 ),
                 Subject(
                     id: UUID(),
-                    name: "Architecture de projetc C# .NET (1)",
+                    name: "Architecture de projet C# .NET (1)",
                     weight: 5,
                     grade: 14.5/20.0
                 ),
@@ -148,7 +148,7 @@ struct Stub {
             subjects: [
                 Subject(
                     id: UUID(),
-                    name: "Architecture de projetc C# .NET (2)",
+                    name: "Architecture de projet C# .NET (2)",
                     weight: 4,
                     grade: 12.17/20.0
                 ),

Graduator/Graduator/Model/Subject.swift

@@ -7,7 +7,7 @@
 
 import Foundation
 
-struct Subject : Identifiable {
+struct Subject : Identifiable, Codable, WeightedGrade {
     let id: UUID
     var name: String
     var weight: Int

Graduator/Graduator/Model/Unit.swift

@@ -7,27 +7,16 @@
 
 import Foundation
 
-struct Unit : Identifiable {
+struct Unit : Identifiable, Codable, WeightedGrade {
     let id: UUID
     var name: String
     var weight: Int
+    var grade: Double? { getAverage() }
     var isProfessional: Bool
     var code: Int
     var subjects: [Subject]
     
     func getAverage() -> Double? {
-        var totalWeight = 0
+        return WeightedAverageCalculator.average(elements: subjects)
-        var weightedSum = 0.0
-
-        for subject in subjects {
-            if let grade = subject.grade {
-                totalWeight += subject.weight
-                weightedSum += grade * Double(subject.weight)
-            }
-        }
-
-        guard totalWeight > 0 else { return nil }
-
-        return weightedSum / Double(totalWeight)
     }
 }

Graduator/Graduator/Model/UnitsManager.swift

@@ -10,28 +10,37 @@ import Foundation
 struct UnitsManager {
     
     var units: [Unit]
+    private var store = UnitsStore()
 
-    func getTotalAverage() -> Double? {
+    public init(units: [Unit] = [], store: UnitsStore = UnitsStore()) {
-        return getAverage(units: units)
+        self.units = units
+        self.store = store
     }
     
-    func getProfessionalAverage() -> Double? {
+    mutating func load() async throws {
-        return getAverage(units: units.filter { $0.isProfessional })
+        do {
+            self.units = try await store.load(defaultValue: Stub.units)
+        } catch {
+            // DEV: this should be replaced with proper error handling before ever going to prod
+            print("ERROR: Failed to load...")
+        }
     }
     
-    func getAverage(units: [Unit]) -> Double? {
+    func save() async throws {
-        var totalWeight = 0
+        do {
-        var weightedSum = 0.0
+            try await store.save(elements: units)
-
+        } catch {
-        for unit in units {
+            // DEV: this should be replaced with proper error handling before ever going to prod
-            if let grade = unit.getAverage() {
+            print("ERROR: Failed to save...")
-                totalWeight += unit.weight
-                weightedSum += grade * Double(unit.weight)
         }
     }
     
-        guard totalWeight > 0 else { return nil }
+    func getTotalAverage() -> Double? {
+        return WeightedAverageCalculator.average(elements: units)
+    }
     
-        return weightedSum / Double(totalWeight)
+    func getProfessionalAverage() -> Double? {
+        let professionalUnits = units.filter { $0.isProfessional }
+        return WeightedAverageCalculator.average(elements: professionalUnits)
     }
 }

Graduator/Graduator/Model/WeightedAverageCalculator.swift

@@ -0,0 +1,26 @@
+//
+//  WeightedAverageCalculator.swift
+//  Graduator
+//
+//  Created by etudiant on 2023-06-10.
+//
+
+import Foundation
+
+struct WeightedAverageCalculator {
+    static func average<T: WeightedGrade>(elements: [T]) -> Double? {
+        var totalWeight = 0
+        var weightedSum = 0.0
+
+        for element in elements {
+            if let grade = element.grade {
+                totalWeight += element.weight
+                weightedSum += grade * Double(element.weight)
+            }
+        }
+
+        guard totalWeight > 0 else { return nil }
+
+        return weightedSum / Double(totalWeight)
+    }
+}

Graduator/Graduator/Model/WeightedGrade.swift

@@ -0,0 +1,13 @@
+//
+//  WeightedGrade.swift
+//  Graduator
+//
+//  Created by etudiant on 2023-06-10.
+//
+
+import Foundation
+
+protocol WeightedGrade {
+    var weight: Int { get }
+    var grade: Double? { get }
+}

Graduator/Graduator/View/Cells/SubjectViewCell.swift

@@ -33,9 +33,16 @@ struct SubjectViewCell: View {
                                 .frame(width: 40)
                                 .onChange(of: isGradeEditable) { value in
                                     if !value {
+                                        Task {
+                                            do {
                                                 subjectVM.onEdited()
                                                 unitVM.updateSubject(subjectVM)
-                                        unitsManagerVM.updateUnit(unitVM)
+                                                try await unitsManagerVM.updateUnit(unitVM)
+                                            } catch {
+                                                // DEV: this should be replaced with proper error handling before ever going to prod
+                                                print("ERROR: Failed to update grade: \(error)")
+                                            }
+                                        }
                                     }
                                 }
                             Image(systemName: isGradeEditable ? "checkmark" : "lock.open")

Graduator/Graduator/View/Views/UnitView.swift

@@ -19,7 +19,6 @@ struct UnitView: View {
         guard let index = offsets.first else { return }
         let subjectVMToDelete = unitVM.SubjectsVM[index]
         unitVM.deleteSubject(subjectVMToDelete)
-        unitsManagerVM.updateUnit(unitVM)
     }
     
     var body: some View {
@@ -77,16 +76,25 @@ struct UnitView: View {
                         Image(systemName: "plus")
                     }
                     Button(action: {
+                        unitVM.isEdited = false
                         unitsManagerVM.isAllEditable.toggle()
                         unitVM.onEdited(isCancelled: true)
+                        unitVM.SubjectsVM.forEach { $0.onEdited(isCancelled: true) }
                     }) {
                         Text("Annuler")
                     }
                     Button(action: {
+                        Task {
+                            do {
                                 unitsManagerVM.isAllEditable.toggle()
                                 unitVM.onEdited()
                                 unitVM.updateAllSubjects()
-                        unitsManagerVM.updateUnit(unitVM)
+                                try await unitsManagerVM.updateUnit(unitVM)
+                            } catch {
+                                // DEV: this should be replaced with proper error handling before ever going to prod
+                                print("ERROR: Failed to update unit: \(error)")
+                            }
+                        }
                     }) {
                         Text("OK")
                     }
@@ -107,9 +115,16 @@ struct UnitView: View {
                             leading: Button("Annuler") { showingForm = false },
                             trailing: Button("Enregistrer") {
                                 if let newSubject = formVM.createSubject() {
+                                    Task {
+                                        do {
                                             unitVM.addSubject(newSubject)
-                                    unitsManagerVM.updateUnit(unitVM)
+                                            try await unitsManagerVM.updateUnit(unitVM)
                                             showingForm = false
+                                        } catch {
+                                            // DEV: this should be replaced with proper error handling before ever going to prod
+                                            print("ERROR: Failed to create unit: \(error)")
+                                        }
+                                    }
                                 } else {
                                     showAlert = true
                                 }
@@ -124,6 +139,7 @@ struct UnitView: View {
         // If user navigates back while editing but before clicking 'OK', the changes are cancelled
         .onDisappear(perform: {
             if unitsManagerVM.isAllEditable {
+                unitVM.isEdited = false
                 unitVM.onEdited(isCancelled: true)
                 unitsManagerVM.isAllEditable = false
             }

Graduator/Graduator/ViewModel/UnitVM.swift

@@ -60,7 +60,7 @@ class UnitVM : ObservableObject, Identifiable {
     init(unit: Unit) {
         original = unit
         model = original.data
-        subjectsVM = unit.subjects.map { SubjectVM(subject: $0) }
+        subjectsVM = original.subjects.map { SubjectVM(subject: $0) }
     }
     
     convenience init() {

Graduator/Graduator/ViewModel/UnitsManagerVM.swift

@@ -44,7 +44,6 @@ class UnitsManagerVM : ObservableObject {
     
     private var original: UnitsManager
     @Published var model: UnitsManager.Data
-    @Published var isEdited: Bool = false
     @Published var isAllEditable: Bool = false
     
     private var unitsVM: [UnitVM]
@@ -54,18 +53,39 @@ class UnitsManagerVM : ObservableObject {
     init(unitsManager: UnitsManager) {
         original = unitsManager
         model = original.data
-        unitsVM = unitsManager.units.map { UnitVM(unit: $0) }
+        unitsVM = original.units.map { UnitVM(unit: $0) }
     }
     
     convenience init() {
         self.init(unitsManager: UnitsManager(units: []))
     }
     
-    func updateUnit(_ unitVM: UnitVM) {
+    func load() async throws {
+        do {
+            try await original.load()
+            DispatchQueue.main.async {
+                self.model = self.original.data
+                self.unitsVM = self.original.units.map { UnitVM(unit: $0) }
+            }
+        } catch {
+            // DEV: this should be replaced with proper error handling before ever going to prod
+            print("ERROR: Failed to load VM...")
+        }
+    }
+    
+    func updateUnit(_ unitVM: UnitVM) async throws {
         guard let index = unitsVM.firstIndex(where: { $0.id == unitVM.id }) else { return }
         let updatedUnit = unitsVM[index].model
         original.units[index].update(from: updatedUnit)
-        model = original.data
+        do {
+            try await original.save()
+            DispatchQueue.main.async {
+                self.model = self.original.data
+            }
+        } catch {
+            // DEV: this should be replaced with proper error handling before ever going to prod
+            print("ERROR: Failed to save VM...")
+        }
     }
     
     var TotalAverage: Double? {

README.md

@@ -9,6 +9,14 @@ Graduator is an iOS application developed with SwiftUI that helps users manage t
 
 Beyond those basic features, some details need to be specified here.
 
+### Persistence
+
+The data is set to be persisted, unless you're using XCode's previewer canvas. 
+
+The local persistence solution has been tested manually on the iOS Simulator.
+
+Upon first launching the app, it is set up to load a stub.
+
 ### Weighted average
 
 A weighted average means that a `subject` or `unit`'s weight plays a part in calculating the average. Users can observe that increasing the weight of a `subject`, for instance, will make the average of the parent `unit` tend more towards that `subject`'s grade.
@@ -39,6 +47,7 @@ After a grade was changed, in order to save the change and to see it reflected i
 
 Finally, users can create  a `subject` when in edit mode. After clicking on *'Modifier'*, look for a `+` in the top navigation bar.
 
+<img src="./docs/delete_2.png" height="700" style="margin:20px" alt="subject deleted">
 <img src="./docs/create_1.png" height="700" style="margin:20px" alt="creating a subject">
 <img src="./docs/create_2.png" height="700" style="margin:20px" alt="subject created">
  
@@ -130,9 +139,9 @@ classDiagram
 
 It might be useful to note that, just like `UnitVM`s aggregate `SubjectVM`s, `Unit`s aggregate
 `Subject`s, but these relationship between `Model` entities were removed from the diagram above for clarity.
-The same is true with the View-related classes.
+The same is true with the `View`-related classes.
 
-Here is the diagram with those relationships depicted.
+Here is the diagram with those relationships depicted, and the local persistence solution added.
 
 
 
@@ -146,6 +155,7 @@ classDiagram
 
     class UnitsManagerVM {
         -original: UnitsManager
+        +load()
         +model: UnitsManager.Data
         +isEdited: Bool
         +isAllEditable: Bool
@@ -175,6 +185,9 @@ classDiagram
 
 
     class UnitsManager {
+        -store: UnitsStore
+        +save()
+        +load()
         +getTotalAverage(): Double?
         +getProfessionalAverage(): Double?
         +getAverage(units: Unit[]): Double?
@@ -199,6 +212,11 @@ classDiagram
         +update(from: Data)
     }
     
+    class UnitsStore {
+        +load<T: Codable>(defaultValue: T[])
+        +save<T: Codable>(elements: T[])
+    }
+
     MainView --> "*" UnitView
     MainView --> UnitsManagerVM
     UnitView --> "*" SubjectViewCell
@@ -215,5 +233,8 @@ classDiagram
     SubjectVM --> Subject
 
     UnitsManager --> "*" Unit
+    UnitsManager --> UnitsStore
+    UnitsManager --> Stub
+    Stub --> "*" Unit
     Unit --> "*" Subject
 ```