Example.swift

struct TemplatesRequest: PidgeonRequest {
    let relativeUrl: String = "/templates"
    let httpMethod: PidgeonHTTPMethod = .get
}

struct UploadRequest: PidgeonRequest {
    let relativeUrl: String = "/exerciseRoutines"
    let httpMethod: PidgeonHTTPMethod = .post
    let routine: ExerciseRoutine

    var body: PidgeonBody? {
        guard let data = try? JSONEncoder().encode(self.routine) else {
            return nil
        }

        return PidgeonBody.jsonData(data)
    }
}

struct ExampleFunctions {
  let executor = DefaultRequestExecutor(DefaultPidgeonRequestFactory(baseUrl: URL("https://yourhost.com")!, defaultHeaders: nil))
  
  func fetchTemplates() -> Single<[ExerciseTemplate]> {
    return self.requestExecutor.rx_perform(request: TemplatesRequest()).map({ (response) -> [ExerciseTemplate] in
        return try response.decode([ExerciseTemplate].self)
    }).asSingle()
  }

  func store(routine: ExerciseRoutine) -> Completable {
     return self.requestExecutor.rx_perform(request: UploadRequest(routine: routine))
      .asCompletable()
  }
}

KeychainAuthStorage.swift

import UIKit
import KeychainAccess

class KeychainAuthStorage: PidgeonAuthTokenStorage {
    let service: String
    let authStorageKey: String
    private let keychain: Keychain
    
    init(service: String, authStorageKey: String) {
        self.service = service
        self.authStorageKey = authStorageKey
        self.keychain = Keychain(service: self.service)
    }
    
    private var hasTriedToReadAuthResultFromKeychain: Bool = false
    private var _authResult: PidgeonAuthResult?
    var authResult: PidgeonAuthResult? {
        set(value) {
            self._authResult = authResult
            if let value = value, let serialized = try? JSONEncoder().encode(value) {
                try? self.keychain.set(serialized, key: self.authStorageKey)
            } else {
                try? self.keychain.remove(self.authStorageKey)
            }
        }
        
        get {
            if self._authResult != nil || self.hasTriedToReadAuthResultFromKeychain {
                return self._authResult
            }
            
            guard let data: Data = (try? self.keychain.getData(self.authStorageKey)) ?? nil else {
                return nil
            }
            
            _authResult =  try? JSONDecoder().decode(PidgeonAuthResult.self, from: data)
            self.hasTriedToReadAuthResultFromKeychain = true
            return _authResult
        }
    }
    
    func clearStorage() {
        self.authResult = nil
    }
}

Pidgeon.swift

import Foundation

struct PidgeonConfig {
    static var defaultDecoder: JSONDecoder = JSONDecoder()
    static var defaultEncoder: JSONEncoder = JSONEncoder()
}

struct PidgeonResponse {
    let response: URLResponse
    let data: Data?
}

enum PidgeonError: Error {
    case invalidHttpCode(code: Int)
    case invalidRequest(request: PidgeonRequest)
    case invalidResponse(response: URLResponse)
    case internalInconsistency
    case noDataToDecode
}

protocol PidgeonRequestFactory {
    var baseUrl: URL { get }
    var defaultHeaders: [String: String]? { get }
    func createURLRequest(from request: PidgeonRequest) throws -> URLRequest
}

extension PidgeonRequestFactory {
    var defaultHeaders: [String: String]? {
        return nil
    }
    
    func createURLRequest(from request: PidgeonRequest) throws -> URLRequest  {
        guard let url = URL(string: request.relativeUrl, relativeTo: self.baseUrl),
            var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true) else {
            fatalError("Invalid request URL")
        }
        
        urlComponents.queryItems = request.parameters?.map({ (k,v) in
            return URLQueryItem(name: k, value: v)
        })
        
        let urlWithParameters = try! urlComponents.asURL()
        var urlRequest = URLRequest(url: urlWithParameters, cachePolicy: request.cachePolicy, timeoutInterval: request.timeoutInterval)
        self.defaultHeaders?.forEach({ (key, value) in
            urlRequest.setValue(value, forHTTPHeaderField: key)
        })
        
        urlRequest.httpMethod = request.httpMethod.rawValue
        
        // Additional headers take precedence
        request.additionalHeaders?.forEach({ (key,value) in
            urlRequest.setValue(value, forHTTPHeaderField: key)
        })
        
        let body = request.body
        urlRequest.httpBody = try body?.data()
        if let contentType = body?.contentType {
            urlRequest.setValue(contentType, forHTTPHeaderField: "Content-Type")
        }
        
        return urlRequest
    }
}

struct DefaultPidgeonRequestFactory: PidgeonRequestFactory {
    let baseUrl: URL
    let defaultHeaders: [String: String]?
}

enum PidgeonHTTPMethod: String {
    case options = "OPTIONS"
    case get     = "GET"
    case head    = "HEAD"
    case post    = "POST"
    case put     = "PUT"
    case patch   = "PATCH"
    case delete  = "DELETE"
    case trace   = "TRACE"
    case connect = "CONNECT"
}

typealias PidgeonRequestErrorTransformer = (_ data: Data?, _ error: Error) -> Error?

enum PidgeonBody {
    case jsonData(Data)
    case json([String: Any])
    case data(Data)
    
    func data() throws -> Data? {
        switch self {
        case .jsonData(let jsonData):
            return jsonData
        case .json(let json):
            return try JSONSerialization.data(withJSONObject: json, options: [])
        case .data(let data):
            return data
        }
    }
    
    var contentType: String? {
        switch self {
        case .json(_), .jsonData(_):
            return "application/json"
        case .data(_):
            return "application/octet-stream"
        }
    }
}

protocol PidgeonRequest {
    var relativeUrl: String { get }
    var httpMethod: PidgeonHTTPMethod { get }
    var cachePolicy: URLRequest.CachePolicy { get }
    var additionalHeaders: [String: String]? { get }
    var parameters: [String:String]? { get }
    var body: PidgeonBody? { get }
    var timeoutInterval: TimeInterval { get }
    var errorTransformer: PidgeonRequestErrorTransformer? { get }
}

extension PidgeonRequest {
    var cachePolicy: URLRequest.CachePolicy {
        return URLRequest.CachePolicy.useProtocolCachePolicy
    }
    
    var additionalHeaders: [String: String]? { return nil }
    var parameters: [String:String]? { return nil }
    var body: PidgeonBody? { return nil }
    var timeoutInterval: TimeInterval { return 30 }
    var errorTransformer: PidgeonRequestErrorTransformer? { return nil }
}

protocol PidgeonRequestTask {
    func cancelTask()
}

typealias RequestExecutorPerformCallback = (_ result: PidgeonResult) -> Void

protocol PidgeonRequestExecutor {
    var requestFactory: PidgeonRequestFactory { get }
    @discardableResult
    func perform(request: PidgeonRequest, completion: @escaping RequestExecutorPerformCallback) -> PidgeonRequestTask?
}

enum PidgeonResult {
    case result(Data?, URLResponse)
    case error(Error)
}

extension PidgeonResult {
    func decode<T: Decodable>(_ type: T.Type,
                              injecting injectedJSON: [String: Any]? = nil,
                              decoder: JSONDecoder = PidgeonConfig.defaultDecoder) throws -> T {
        switch self {
        case .error(let error):
            throw error
        case .result(let data, _):
            return try self.decodeData(data: data, type: type, injecting: injectedJSON, decoder: decoder)
        }
    }
    
    private func decodeData<T: Decodable>(data: Data?,
                                          type: T.Type,
                                          injecting injectedJSON: [String: Any]?,
                                          decoder: JSONDecoder) throws -> T {
        guard let data = data else {
            throw PidgeonError.noDataToDecode
        }
        
        guard let injectedJSON = injectedJSON else {
            return try decoder.decode(type, from: data)
        }
        
        let jsonObject = try JSONSerialization.jsonObject(with: data, options: [])
        let modifiedJSON: Any = {
            // Inject injected data into json object
            if var json = jsonObject as? [String: Any] {
                injectedJSON.forEach { k in
                    json[k.key] = k.value
                }
                
                return json
            } else if var jsonArray = jsonObject as? [[String: Any]] {
                // Inject injected data into every object in the json array
                jsonArray.enumerated().forEach { i, jsonObj in
                    var mutableJsonObj = jsonObj
                    injectedJSON.forEach { k in
                        mutableJsonObj[k.key] = k.value
                    }
                    jsonArray[i] = mutableJsonObj
                }
                return jsonArray
            }
            
            return [:]
        }()
        
        let modifiedData = try JSONSerialization.data(withJSONObject: modifiedJSON, options: [])
        return try decoder.decode(type, from: modifiedData)
    }
    
    func toJson() throws -> [String: Any]? {
        switch self {
        case .error(let error):
            throw error
        case .result(let data, _):
            guard let data = data else { return nil }
            return try JSONSerialization.jsonObject(with: data) as? [String: Any]
        }
    }
}

extension PidgeonResult {
    var error: Error? {
        switch self {
        case .error(let error):
            return error
        default:
            return nil
        }
    }
    
    var data: Data? {
        switch self {
        case .result(let data, _):
            return data
        default:
            return nil
        }
    }
}

typealias PidgeonAuthTokenProviderFetchCallback = (_ result: PidgeonAuthResult?, _ error: Error?) -> Void

protocol PidgeonAuthTokenStorage {
    var authResult: PidgeonAuthResult? { get set }
    func clearStorage()
}

protocol PidgeonAuthTokenProvider {
    func reauthorize(completion: @escaping PidgeonAuthTokenProviderFetchCallback)
    func login(withRequest: PidgeonRequest, completion: @escaping PidgeonAuthTokenProviderFetchCallback)
    var authStorage: PidgeonAuthTokenStorage { get }
}

typealias PidgeonTokenFetcherBlock = (_ isReauthorizing: Bool, (PidgeonResult) -> Void) -> Void

struct PidgeonAuthResult: Codable, Equatable {
    let timestamp: TimeInterval
    let accessToken: String
    let tokenType: String
    let refreshToken: String
    let expiresInMsec: Int
}

extension PidgeonAuthResult {
    var hasExpired: Bool {
        let expiryTime = self.timestamp + Double(self.expiresInMsec) / 1000
        return Date().timeIntervalSinceNow >= expiryTime
    }
}

protocol PidgeonTokenFetcher {
    func fetchToken(isReauthorizing: Bool, completion: @escaping PidgeonAuthTokenProviderFetchCallback)
}

typealias AuthRequestFactory = (_ authStorage: PidgeonAuthTokenStorage) -> PidgeonRequest?

extension URLSessionDataTask: PidgeonRequestTask {
    func cancelTask() {
        self.cancel()
    }
}

struct DefaultRequestExecutor: PidgeonRequestExecutor {
    let requestFactory: PidgeonRequestFactory
    let urlSession: URLSession
    
    init(requestFactory: PidgeonRequestFactory, urlSession: URLSession = URLSession.shared) {
        self.requestFactory = requestFactory
        self.urlSession = urlSession
    }
    
    func perform(request: PidgeonRequest, completion: @escaping RequestExecutorPerformCallback) -> PidgeonRequestTask? {
        let attemptedRequest: URLRequest? = {
            do {
                return try self.requestFactory.createURLRequest(from: request)
            } catch let error {
                completion(.error(error))
                return nil
            }
        }()
        
        guard let urlRequest = attemptedRequest else {
            return nil
        }
    
        let task = self.urlSession.dataTask(with: urlRequest) { (data, response, error) in
            if let error = error {
                let transformedError = request.errorTransformer?(data, error) ?? error
                DispatchQueue.main.async {
                    completion(.error(transformedError))
                }
                return
            }
        
            guard let httpResponse = response as? HTTPURLResponse else {
                DispatchQueue.main.async {
                    completion(.error(PidgeonError.internalInconsistency))
                }
                return
            }
            
            let isValidHttpCode = (200..<300).contains(httpResponse.statusCode)
            if !isValidHttpCode {
                DispatchQueue.main.async {
                    completion(.error(PidgeonError.invalidHttpCode(code: httpResponse.statusCode)))
                }
                return
            }
            
            DispatchQueue.main.async {
                completion(.result(data, httpResponse))
            }
        }
        
        task.resume()
        return task
    }
}

class DefaultPidgeonAuthTokenProvider: PidgeonAuthTokenProvider {
    enum ProviderError: Error {
        case tokenFetchError(Error)
        case couldNotCreateReauthRequest
        case parseResponseError(Error)
    }
    
    private(set) var authStorage: PidgeonAuthTokenStorage
    let reauthRequestFactory: AuthRequestFactory
    private let authRequestExecutor: PidgeonRequestExecutor
    
    private var pendingReauthRequests: [PidgeonAuthTokenProviderFetchCallback] = []
    
    init(authRequestExecutor: PidgeonRequestExecutor,
         authStorage: PidgeonAuthTokenStorage,
         reauthRequestFactory: @escaping AuthRequestFactory) {
        self.authRequestExecutor = authRequestExecutor
        self.authStorage = authStorage
        self.reauthRequestFactory = reauthRequestFactory
    }
    
    func login(withRequest request: PidgeonRequest, completion: @escaping PidgeonAuthTokenProviderFetchCallback) {
        self.fetchAndStoreAuthToken(withRequest: request, completion: completion)
    }
    
    func reauthorize(completion: @escaping PidgeonAuthTokenProviderFetchCallback) {
        guard let tokenRequest = self.reauthRequestFactory(self.authStorage) else {
            completion(nil, ProviderError.couldNotCreateReauthRequest)
            return
        }
        
        self.pendingReauthRequests.append(completion)
        if self.pendingReauthRequests.count == 1 {
            self.fetchAndStoreAuthToken(withRequest: tokenRequest, completion: { [weak self] authResult, error in
                guard let self = self else { return }
                let pendingRequests = self.pendingReauthRequests
                self.pendingReauthRequests.removeAll()
                pendingRequests.forEach({ (callback) in
                    callback(authResult, error)
                })
            })
        }
    }
    
    func fetchAndStoreAuthToken(withRequest request: PidgeonRequest, completion: @escaping PidgeonAuthTokenProviderFetchCallback) {
        self.authRequestExecutor.perform(request: request) { [weak self] (result) in
            guard let self = self else { return }
            do {
                if let error = result.error {
                    completion(nil, error)
                    return
                }
                
                let authResult = try result.decode(PidgeonAuthResult.self, injecting: [
                    "timestamp": Date().timeIntervalSince1970
                ])
                
                self.authStorage.authResult = authResult
                completion(authResult, nil)
            } catch let error {
                completion(nil, error)
            }
        }
    }
}

RxPidgeon.swift

import RxSwift

extension PidgeonRequestExecutor {
    func rx_perform(request: PidgeonRequest, shouldCancelOnDispose: Bool = false) -> Single<PidgeonResult> {
        let factory = {
            return Single<PidgeonResult>.create(subscribe: { (single) -> Disposable in
                let task = self.perform(request: request, completion: { result in
                    single(.success(result))
                })
                
                return Disposables.create {
                    if shouldCancelOnDispose {
                        task?.cancelTask()
                    }
                }
            })
        }
        
        return Single.deferred(factory)
    }
}