[Libraries] Dependency (#6)

This PR contains the work that implements the Dependency service, which is used as a dependency injection mechanism in the application.

To give further details on what was done:
- [x] created the `Dependency` library into the **Libraries** package;
- [x] defined the `DependencyKey` protocol;
- [x] implemented the `DependencyService` service;
- [x] implemented the `Dependency` property wrapper.

Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Reviewed-on: rock-n-code/deep-linking-assignment#6

Apps/Locations/Libraries/Package.swift

@@ -11,7 +11,9 @@ let package = Package(
         .library(
             name: "Libraries",
             targets: [
-                "Locations"
+                "Dependency",
+                "Locations",
+                "Persistence"
             ]
         ),
     ],
@@ -21,6 +23,10 @@ let package = Package(
             name: "APICore",
             dependencies: []
         ),
+        .target(
+            name: "Dependency",
+            dependencies: []
+        ),
         .target(
             name: "Locations",
             dependencies: [
@@ -37,6 +43,12 @@ let package = Package(
                 "APICore"
             ]
         ),
+        .testTarget(
+            name: "DependencyTests",
+            dependencies: [
+                "Dependency"
+            ]
+        ),
         .testTarget(
             name: "LocationsTests",
             dependencies: [

Apps/Locations/Libraries/Sources/Dependency/Property Wrappers/Dependency.swift

@@ -0,0 +1,31 @@
+//
+//  Dependency.swift
+//  Dependency
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This property wrapper provides a direct connection to the `DependencyService` service.
+@propertyWrapper
+public struct Dependency<D> {
+    
+    // MARK: Properties
+    
+    private let keyPath: WritableKeyPath<DependencyService, D>
+    
+    /// This property allows direct read/write access to a defined dependency attached to a selected key path.
+    public var wrappedValue: D {
+        get { DependencyService[keyPath] }
+        set { DependencyService[keyPath] = newValue }
+    }
+    
+    // MARK: Initialisers
+    
+    /// Initialise the property wrapper by setting a key path to a defined dependency.
+    /// - Parameter keyPath: A key path to a defined dependency in the `DependencyService` service.
+    public init(_ keyPath: WritableKeyPath<DependencyService, D>) {
+        self.keyPath = keyPath
+    }
+
+}

Apps/Locations/Libraries/Sources/Dependency/Protocols/DependencyKey.swift

@@ -0,0 +1,22 @@
+//
+//  DependencyKey.swift
+//  Dependency
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This protocol defines a key to use in the dependency service.
+public protocol DependencyKey {
+    
+    // MARK: Associated types
+    
+    /// The associated type representing the type of the dependency key's value.
+    associatedtype Value
+    
+    // MARK: Properties
+    
+    /// The default value for the dependency key.
+    static var currentValue: Value { get set }
+    
+}

Apps/Locations/Libraries/Sources/Dependency/Services/DependencyService.swift

@@ -0,0 +1,28 @@
+//
+//  DependencyService.swift
+//  Dependency
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+/// This service provide write/read access to the injected dependencies.
+public struct DependencyService {
+    
+    // MARK: Properties
+    
+    private static var current = DependencyService()
+    
+    // MARK: Subscripts
+
+    public static subscript<DK: DependencyKey>(key: DK.Type) -> DK.Value {
+        get { key.currentValue }
+        set { key.currentValue = newValue }
+    }
+    
+    public static subscript<D>(_ keyPath: WritableKeyPath<DependencyService, D>) -> D {
+        get { current[keyPath: keyPath] }
+        set { current[keyPath: keyPath] = newValue }
+    }
+
+}

Apps/Locations/Libraries/Tests/DependencyTests/Helpers/TestServices.swift

@@ -0,0 +1,34 @@
+//
+//  TestServices.swift
+//  DependencyTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Dependency
+
+// MARK: - Protocols
+
+protocol TestService {}
+
+// MARK: - Services
+
+struct SomeService: TestService, Equatable {}
+struct SomeOtherService: TestService, Equatable {}
+
+// MARK: - DependencyKey
+
+struct TestServiceKey: DependencyKey {
+    static var currentValue: TestService = SomeService()
+}
+
+// MARK: - DependencyService+Keys
+
+extension DependencyService {
+    var testService: TestService {
+        get { Self[TestServiceKey.self] }
+        set { Self[TestServiceKey.self] = newValue }
+    }
+}
+

Apps/Locations/Libraries/Tests/DependencyTests/Property Wrappers/DependencyTests.swift

@@ -0,0 +1,74 @@
+//
+//  DependencyTests.swift
+//  DependencyTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import XCTest
+
+@testable import Dependency
+
+final class DependencyTests: XCTestCase {
+    
+    // MARK: Properties
+    
+    private var subject: TestSubject!
+    
+    // MARK: Setup
+    
+    override func setUp() {
+        DependencyService[\.testService] = SomeService()
+    }
+    
+    // MARK: Tests
+
+    func test_readTestService() {
+        // GIVEN
+        subject = .init()
+        
+        // WHEN
+        let service = subject.testService
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+    
+    func test_writeDependencyKey() async throws {
+        // GIVEN
+        subject = .init()
+        
+        subject.testService = SomeOtherService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeOtherService)
+    }
+    
+    func test_writeDependencyKeyTwice() async throws {
+        // GIVEN
+        subject = .init()
+        
+        subject.testService = SomeOtherService()
+        subject.testService = SomeService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+
+}
+
+// MARK: - TestSubject
+
+private struct TestSubject {
+    @Dependency(\.testService) var testService
+}

Apps/Locations/Libraries/Tests/DependencyTests/Services/DependencyServiceTests.swift

@@ -0,0 +1,58 @@
+//
+//  DependencyServiceTests.swift
+//  DependencyTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import XCTest
+
+@testable import Dependency
+
+final class DependencyServiceTests: XCTestCase {
+
+    // MARK: Setup
+    
+    override func setUp() {
+        DependencyService[\.testService] = SomeService()
+    }
+    
+    // MARK: Tests
+
+    func test_readDependencyKey() async throws {
+        // GIVEN
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+    
+    func test_writeDependencyKey() async throws {
+        // GIVEN
+        DependencyService[\.testService] = SomeOtherService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeOtherService)
+    }
+    
+    func test_writeDependencyKeyTwice() async throws {
+        // GIVEN
+        DependencyService[\.testService] = SomeOtherService()
+        DependencyService[\.testService] = SomeService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+
+}