From 72d59acb08f20456d19e6472fcd989ed8728c474 Mon Sep 17 00:00:00 2001
From: Javier Cicchelli <javier@rock-n-code.com>
Date: Sun, 16 Apr 2023 20:30:34 +0200
Subject: [PATCH] Implemented the MockURLProtocol protocol to mock remote
 requests/responses when using URLSession instances.

---
 .../Classes/MockURLProtocol.swift             | 99 +++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 Sources/Communications/Classes/MockURLProtocol.swift

diff --git a/Sources/Communications/Classes/MockURLProtocol.swift b/Sources/Communications/Classes/MockURLProtocol.swift
new file mode 100644
index 0000000..e8a0fd3
--- /dev/null
+++ b/Sources/Communications/Classes/MockURLProtocol.swift
@@ -0,0 +1,99 @@
+//
+//  MockURLProtocol.swift
+//  APICore
+//
+//  Created by Javier Cicchelli on 10/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Foundation
+
+/// This class overrides the `URLProtocol` protocol used by the `URLSession` to handle the loading of protocol-specific URL data so it is possible to mock URL response for testing purposes.
+public class MockURLProtocol: URLProtocol {
+    
+    // MARK: Properties
+    
+    public static var mockData: [MockURLRequest: MockURLResponse] = [:]
+    
+    // MARK: Functions
+    
+    public override class func canInit(with task: URLSessionTask) -> Bool {
+        true
+    }
+    
+    public override class func canInit(with request: URLRequest) -> Bool {
+        true
+    }
+    
+    public override class func canonicalRequest(for request: URLRequest) -> URLRequest {
+        request
+    }
+    
+    public override func startLoading() {
+        guard
+            let httpMethod = request.httpMethod,
+            let method = HTTPRequestMethod(rawValue: httpMethod),
+            let url = request.url,
+            let response = Self.mockData[.init(
+                method: method,
+                url: url
+            )]
+        else {
+            client?.urlProtocolDidFinishLoading(self)
+            return
+        }
+        
+        if let data = response.data {
+            client?.urlProtocol(self, didLoad: data)
+        }
+        
+        if let httpResponse = HTTPURLResponse(
+            url: url,
+            statusCode: response.status.rawValue,
+            httpVersion: nil,
+            headerFields: response.headers
+        ) {
+            client?.urlProtocol(
+                self,
+                didReceive: httpResponse, 
+                cacheStoragePolicy: .allowedInMemoryOnly
+            )
+        }
+
+        client?.urlProtocolDidFinishLoading(self)
+    }
+    
+    public override func stopLoading() {}
+
+}
+
+// MARK: - Structs
+
+///  This model includes the data to be injected into an specific URL at the time of mocking its request.
+public struct MockURLRequest: Hashable {
+    public let method: HTTPRequestMethod
+    public let url: URL
+}
+
+///  This model includes the data to be injected into an specific URL at the time of mocking its response.
+public struct MockURLResponse {
+    
+    // MARK: Properties
+    
+    public let status: HTTPResponseCode
+    public let headers: [String: String]
+    public let data: Data?
+    
+    // MARK: Initialisers
+    
+    public init(
+        status: HTTPResponseCode,
+        headers: [String : String] = [:],
+        data: Data? = nil
+    ) {
+        self.status = status
+        self.headers = headers
+        self.data = data
+    }
+
+}