iOS Stripe 支付（绑卡，Apple Pay）、退款、提现集成总结!

// 1. 初始化填写信用卡的输入框
lazy var paymentCardTextField: STPPaymentCardTextField = {
    let textField = STPPaymentCardTextField()
    textField.isHidden = false
    textField.delegate = self
    
    // 可定制 TextField 的主题外观
    textField.backgroundColor = STPTheme.default().secondaryBackgroundColor
    textField.textColor = STPTheme.default().primaryForegroundColor
    textField.placeholderColor = STPTheme.default().secondaryForegroundColor
    textField.borderColor = UIColor.gxd_themeColor()
    textField.borderWidth = 1.0
    textField.textErrorColor = STPTheme.default().errorColor
    textField.postalCodeEntryEnabled = true
    return textField
}()
// 2. 设置可发布的秘钥：从 Stripe 管理后台拿到，也可以又服务器保存，然后下发到客户端
Stripe.setDefaultPublishableKey("\(PublishableKey)")
// 3. 向服务端发起一个预支付请求，服务端通过调用 Stripe 的 API 生成 paymentIntent对象，下发 paymentIntentClientSecret 到客户端
func startCheckout() {
    // Create a PaymentIntent by calling the sample server's /create-payment-intent endpoint.
    let url = URL(string: BackendUrl + "create-payment-intent")!
    let json: [String: Any] = [
        "currency": "usd",
        "items": [
            ["id": "photo_subscription"]
        ]
    ]
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.httpBody = try? JSONSerialization.data(withJSONObject: json)
    let task = URLSession.shared.dataTask(with: request, completionHandler: { [weak self] (data, response, error) in
        guard let response = response as? HTTPURLResponse,
            response.statusCode == 200,
            let data = data,
            let json = try? JSONSerialization.jsonObject(with: data, options: []) as? [String : Any],
            let clientSecret = json["clientSecret"] as? String,
            let publishableKey = json["publishableKey"] as? String else {
                let message = error?.localizedDescription ?? "Failed to decode response from server."
                self?.displayAlert(title: "Error loading page", message: message)
                return
        }
        print("Created PaymentIntent")
        self?.paymentIntentClientSecret = clientSecret
        // Configure the SDK with your Stripe publishable key so that it can make requests to the Stripe API
        // For added security, our sample app gets the publishable key from the server
        Stripe.setDefaultPublishableKey(publishableKey)
    })
    task.resume()
}
// 4. 收集用户输入的信用卡信息，客户端拿到这个 clientSecret，发起支付请求
guard let paymentIntentClientSecret = paymentIntentClientSecret else {
    return;
}
// Collect card details
let cardParams = cardTextField.cardParams
let paymentMethodParams = STPPaymentMethodParams(card: cardParams, billingDetails: nil, metadata: nil)
let paymentIntentParams = STPPaymentIntentParams(clientSecret: paymentIntentClientSecret)
paymentIntentParams.paymentMethodParams = paymentMethodParams
// Submit the payment
let paymentHandler = STPPaymentHandler.shared()
paymentHandler.confirmPayment(withParams: paymentIntentParams, authenticationContext: self) { (status, paymentIntent, error) in
    switch (status) {
    case .failed:
        self.displayAlert(title: "Payment failed", message: error?.localizedDescription ?? "")
        break
    case .canceled:
        self.displayAlert(title: "Payment canceled", message: error?.localizedDescription ?? "")
        break
    case .succeeded:
        self.displayAlert(title: "Payment succeeded", message: paymentIntent?.description ?? "", restartDemo: true)
        break
    @unknown default:
        fatalError()
        break
    }
}
// 有些卡需要用户二次验证授权，提供一个代理，弹出让用户确认验证的控制器
extension CheckoutViewController: STPAuthenticationContext {
    func authenticationPresentingViewController() -> UIViewController {
        return self
    }
}

// 请求服务端，查询这个用户是否有创建过 Stripe Customer 用户，如果有，返回该 Stripe Customer 用户的绑卡信息（绑了多少张卡，选中的支付方式是哪个），没有就创建一个新的
// 这是个代理方法，是由 Stripe 代理
func createCustomerKey(withAPIVersion apiVersion: String, completion: @escaping STPJSONResponseCompletionBlock) {
    let url = self.baseURL.appendingPathComponent("ephemeral_keys")
    var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: false)!
    urlComponents.queryItems = [URLQueryItem(name: "api_version", value: apiVersion)]
    var request = URLRequest(url: urlComponents.url!)
    request.httpMethod = "POST"
    let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
        guard let response = response as? HTTPURLResponse,
            response.statusCode == 200,
            let data = data,
            let json = ((try? JSONSerialization.jsonObject(with: data, options: []) as? [String : Any]) as [String : Any]??) else {
            completion(nil, error)
            return
        }
        completion(json, nil)
    })
    task.resume()
}

func createPaymentIntent(products: [Product], shippingMethod: PKShippingMethod?, country: String? = nil, completion: @escaping ((Result<String, Error>) -> Void)) {
    let url = self.baseURL.appendingPathComponent("create_payment_intent")
    var params: [String: Any] = [
        "metadata": [
            // example-mobile-backend allows passing metadata through to Stripe
            "payment_request_id": "B3E611D1-5FA1-4410-9CEC-00958A5126CB",
        ],
    ]
    params["products"] = products.map({ (p) -> String in
        return p.emoji
    })
    if let shippingMethod = shippingMethod {
        params["shipping"] = shippingMethod.identifier
    }
    params["country"] = country
    let jsonData = try? JSONSerialization.data(withJSONObject: params)
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    request.httpBody = jsonData
    let task = URLSession.shared.dataTask(with: request, completionHandler: { (data, response, error) in
        guard let response = response as? HTTPURLResponse,
            response.statusCode == 200,
            let data = data,
            let json = ((try? JSONSerialization.jsonObject(with: data, options: []) as? [String : Any]) as [String : Any]??),
            let secret = json?["secret"] as? String else {
                completion(.failure(error ?? APIError.unknown))
                return
        }
        completion(.success(secret))
    })
    task.resume()
}

// 1.-------------------------- 初始化 STPPaymentContext 上下文 --------------------------
// 设置服务端的请求的地址
MyAPIClient.sharedClient.baseURLString = self.backendBaseURL
// 设置可发布的秘钥
Stripe.setDefaultPublishableKey(self.stripePublishableKey)
// 支付相关配置
let config = STPPaymentConfiguration.shared()
// 设置 Apple Pay 配置的商户 ID
config.appleMerchantIdentifier = self.appleMerchantID
// 设置支付方式额外选项，是一个选项枚举，指定支付方式包含哪些（只是信用卡、还是既有信用卡还宝行 Apple Pay）
// 注意的是：就算这里制定了 Apple Pay，如果 Apple Pay 的相关配置没有检测通过，真实出现的时候也是没有 Apple Pay 这种支付方式的
config.additionalPaymentOptions = settings.additionalPaymentOptions
// 是否支持可以扫描添加卡
config.cardScanningEnabled = true
// 支付的币种
self.paymentCurrency = settings.currency
let customerContext = STPCustomerContext(keyProvider: MyAPIClient.sharedClient)
let paymentContext = STPPaymentContext(customerContext: customerContext,
                                       configuration: config,
                                       theme: settings.theme)
paymentContext.paymentCurrency = self.paymentCurrency
// 2.------------------ 发起支付 ------------------------------------
self.paymentContext.requestPayment()
// 3. -- ------------------------- STPPaymentContextDelegate 回调 -----------------
func paymentContext(_ paymentContext: STPPaymentContext, didCreatePaymentResult paymentResult: STPPaymentResult, completion: @escaping STPPaymentStatusBlock) {
     // Create the PaymentIntent on the backend
     // To speed this up, create the PaymentIntent earlier in the checkout flow and update it as necessary (e.g. when the cart subtotal updates or when shipping fees and taxes are calculated, instead of re-creating a PaymentIntent for every payment attempt.
    

}
// 支付完成回调
func paymentContext(_ paymentContext: STPPaymentContext, didFinishWith status: STPPaymentStatus, error: Error?) {
}
// 支付上下文发生改变回调
func paymentContextDidChange(_ paymentContext: STPPaymentContext) {
}
// 支付错误回调
func paymentContext(_ paymentContext: STPPaymentContext, didFailToLoadWithError error: Error) {
}

// 1. 拼接授权 URl 
// clientId 是商户在 Stripe 管理后台的唯一 id，和 redirectUri 一样都是在商户 Stripe 管理后台可以查到的
let authorizeURL = "https://connect.stripe.com/express/oauth/authorize" + "?" + "redirect_uri=\(redirectUri)&" + "client_id=\(clientId)&" + "state=\(state)&" + "stripe_user[business_type]=individual"
// 2. 根据WebView对于即将跳转的HTTP请求头信息和相关信息来决定是否跳转，获取用户注册授权完成回传的 code 和 state
func webView(_ webView: WKWebView, decidePolicyFor navigationAction: WKNavigationAction, decisionHandler: @escaping (WKNavigationActionPolicy) -> Void) {
    guard let urlString = navigationAction.request.url?.absoluteString,
        let redirectUrl = model?.redirectUri else {
        decisionHandler(WKNavigationActionPolicy.cancel)
        return
    }
    if urlString.hasPrefix(redirectUrl) {
        print("发生重定向请求：\(urlString)")
        // 截取出回调后面的参数 code，state
        guard let queryParames = navigationAction.request.url?.queryParameters else {
            decisionHandler(WKNavigationActionPolicy.cancel)
            return
        }
        let code = queryParames.filter{ $0.key == "code" }.first?.value ?? ""
        let state = queryParames.filter{ $0.key == "state" }.first?.value ?? ""
        decisionHandler(WKNavigationActionPolicy.cancel)
    } else {
        decisionHandler(WKNavigationActionPolicy.allow)
    }
}