Implemented the PersistenceService service.

Apps/Locations/Libraries/Sources/Persistence/Services/PersistenceService.swift

@@ -0,0 +1,133 @@
+//
+//  PersistenceService.swift
+//  Persistence
+//
+//  Created by Javier Cicchelli on 10/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+
+public struct PersistenceService {
+    
+    // MARK: Properties
+    
+    public static let shared = PersistenceService()
+    public static let inMemory = PersistenceService(inMemory: true)
+    
+    public let container: NSPersistentContainer
+    
+    // MARK: Initialisers
+    
+    init(inMemory: Bool = false) {
+        guard
+            let modelURL = Bundle.module.url(forResource: .Model.name, withExtension: .Model.extension),
+            let managedObjectModel = NSManagedObjectModel(contentsOf: modelURL)
+        else {
+            fatalError("Could not load the model from the library.")
+        }
+
+        container = NSPersistentContainer(
+            name: .Model.name,
+            managedObjectModel: managedObjectModel
+        )
+        
+        setContainer(inMemory)
+    }
+    
+    // MARK: Functions
+    
+    /// Create a private queue context.
+    /// - Returns: A concurrent `NSManagedObjectContext` context instance ready to use.
+    public func makeTaskContext() -> NSManagedObjectContext {
+        let taskContext = container.newBackgroundContext()
+        
+        taskContext.automaticallyMergesChangesFromParent = true
+        taskContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        
+        return taskContext
+    }
+    
+    /// Create a child context of the view context.
+    /// - Returns: A generated child `NSManagedObjectContext` context instance ready to use.
+    public func makeChildContext() -> NSManagedObjectContext {
+        let context = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
+        
+        context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
+        context.parent = container.viewContext
+        context.automaticallyMergesChangesFromParent = true
+        
+        return context
+    }
+    
+    /// Save a given context,
+    /// - Parameter context: A `NSManagedObjectContext` context instance to save.
+    public func save(context: NSManagedObjectContext) {
+        guard context.hasChanges else {
+            return
+        }
+        
+        do {
+            try context.save()
+        } catch {
+            let nserror = error as NSError
+            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
+        }
+    }
+    
+    /// Save a given child context as well as its respective parent context.
+    /// - Parameter context: A child `NSManagedObjectContext` context instance to save.
+    public func save(childContext context: NSManagedObjectContext) {
+        guard context.hasChanges else {
+            return
+        }
+        
+        do {
+            try context.save()
+            
+            guard
+                let parent = context.parent,
+                parent == container.viewContext
+            else {
+                return
+            }
+
+            try parent.performAndWait {
+                try parent.save()
+            }
+        } catch {
+            let nserror = error as NSError
+            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
+        }
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension PersistenceService {
+    func setContainer(_ inMemory: Bool) {
+        container.persistentStoreDescriptions = [
+            NSPersistentStoreDescription(url:
+                inMemory
+                    ? URL(fileURLWithPath: "/dev/null")
+                    : NSPersistentContainer.defaultDirectoryURL().appending(path: "\(String.Model.name).sqlite")
+            )
+        ]
+        container.loadPersistentStores { _, error in
+            if let error = error as NSError? {
+                fatalError("Unresolved error \(error), \(error.userInfo)")
+            }
+        }
+        container.viewContext.automaticallyMergesChangesFromParent = true
+    }
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    enum Model {
+        static let name = "Model"
+        static let `extension` = "momd"
+    }
+}

Apps/Locations/Libraries/Tests/PersistenceTests/Services/PersistenceServiceTests.swift

@@ -0,0 +1,104 @@
+//
+//  PersistenceServiceTests.swift
+//  PersistenceTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import CoreData
+import XCTest
+
+@testable import Persistence
+
+final class PersistenceServiceTests: XCTestCase {
+    
+    // MARK: Properties
+    
+    private var persistence: PersistenceService!
+
+    // MARK: Initialiser tests
+    
+    func test_initByDefault() {
+        // GIVEN
+        // WHEN
+        persistence = .init()
+        
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.lastPathComponent, "Model.sqlite")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    func test_initWithInMemory() {
+        // GIVEN
+        // WHEN
+        persistence = .init(inMemory: true)
+        
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.absoluteString, "file:///dev/null")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    // MARK: Static properties tests
+    
+    func test_shared() {
+        // GIVEN
+        persistence = .shared
+        
+        // WHEN
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.lastPathComponent, "Model.sqlite")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    func test_inMemory() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        // THEN
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.count, 1)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.type, NSSQLiteStoreType)
+        XCTAssertEqual(persistence.container.persistentStoreDescriptions.first?.url?.absoluteString, "file:///dev/null")
+        XCTAssertNotNil(persistence.container.viewContext)
+        XCTAssertTrue(persistence.container.viewContext.automaticallyMergesChangesFromParent)
+    }
+    
+    // MARK: Functions tests
+    
+    func test_makeTaskContext() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        let context = persistence.makeTaskContext()
+        
+        // THEN
+        XCTAssertTrue(context.automaticallyMergesChangesFromParent)
+        XCTAssertTrue(context.mergePolicy as AnyObject === NSMergeByPropertyObjectTrumpMergePolicy)
+        XCTAssertNil(context.parent)
+    }
+    
+    func test_makeChildContext() {
+        // GIVEN
+        persistence = .inMemory
+        
+        // WHEN
+        let context = persistence.makeChildContext()
+        
+        // THEN
+        XCTAssertTrue(context.automaticallyMergesChangesFromParent)
+        XCTAssertTrue(context.mergePolicy as AnyObject === NSMergeByPropertyObjectTrumpMergePolicy)
+        XCTAssertEqual(context.parent, persistence.container.viewContext)
+    }
+
+}