import SwiftUI
import AuthenticationServices  // 苹果登录功能
import Alamofire              // 网络请求
import CryptoKit              // 加密功能

/// 主登录视图 - 处理苹果登录
struct LoginView: View {
    // MARK: - 属性
    @Environment(\.dismiss) private var dismiss  // 用于关闭视图
    @State private var isLoading = false         // 加载状态
    @State private var showError = false         // 是否显示错误
    @State private var errorMessage = ""         // 错误信息
    @State private var currentNonce: String?     // 用于防止重放攻击的随机数
    
    // MARK: - 视图主体
    var body: some View {
        ZStack {
            // 背景
            Color(.systemBackground)
                .edgesIgnoringSafeArea(.all)
            
            // 主要内容
            VStack(spacing: 24) {
                Spacer()
                appHeaderView()      // 应用标题
                signInButton()       // 登录按钮
                Spacer()
                termsAndPrivacyView() // 服务条款和隐私政策
            }
            .padding()
            .alert(isPresented: $showError) {
                Alert(
                    title: Text("Error"),
                    message: Text(errorMessage),
                    dismissButton: .default(Text("OK"))
                )
            }
            
            // 加载指示器
            if isLoading {
                loadingView()
            }
        }
        .navigationBarHidden(true)
    }
    
    // MARK: - 视图组件
    
    /// 应用标题视图
    private func appHeaderView() -> some View {
        VStack(spacing: 16) {
            Image(systemName: "person.circle.fill")
                .resizable()
                .aspectRatio(contentMode: .fit)
                .frame(width: 80, height: 80)
                .foregroundColor(.blue)
            
            Text("Welcome to Wake")
                .font(.largeTitle)
                .fontWeight(.bold)
            
            Text("Sign in to continue")
                .font(.subheadline)
                .foregroundColor(.secondary)
        }
        .padding(.bottom, 40)
    }
    
    /// 苹果登录按钮
    private func signInButton() -> some View {
        SignInWithAppleButton(
            onRequest: { request in
                // 生成随机数用于安全验证
                let nonce = String.randomURLSafeString(length: 32)
                self.currentNonce = nonce
                
                // 配置登录请求
                request.requestedScopes = [.fullName, .email]  // 请求用户全名和邮箱
                request.nonce = self.sha256(nonce)             // 设置nonce
            },
            onCompletion: handleAppleSignIn  // 登录完成处理
        )
        .signInWithAppleButtonStyle(.black)  // 按钮样式
        .frame(height: 50)
        .padding(.horizontal, 40)
        .cornerRadius(10)
    }
    
    /// 服务条款和隐私政策链接
    private func termsAndPrivacyView() -> some View {
        VStack(spacing: 8) {
            Text("By continuing, you agree to our")
                .font(.caption)
                .foregroundColor(.secondary)
            
            HStack(spacing: 16) {
                Button("Terms of Service") {
                    openURL("https://yourwebsite.com/terms")
                }
                .font(.caption)
                .foregroundColor(.blue)
                
                Text("•")
                    .foregroundColor(.secondary)
                
                Button("Privacy Policy") {
                    openURL("https://yourwebsite.com/privacy")
                }
                .font(.caption)
                .foregroundColor(.blue)
            }
        }
        .padding(.bottom, 24)
    }
    
    /// 加载视图
    private func loadingView() -> some View {
        return ZStack {
            Color.black.opacity(0.4)
                .edgesIgnoringSafeArea(.all)
            
            ProgressView()
                .scaleEffect(1.5)
                .progressViewStyle(CircularProgressViewStyle(tint: .white))
        }
    }
    
    // MARK: - 苹果登录处理
    
    /// 处理苹果登录结果
    private func handleAppleSignIn(result: Result<ASAuthorization, Error>) {
        print("🔵 [Apple Sign In] 开始处理登录结果...")
        switch result {
        case .success(let authResults):
            print("✅ [Apple Sign In] 登录授权成功")
            processAppleIDCredential(authResults.credential)
        case .failure(let error):
            print("❌ [Apple Sign In] 登录失败: \(error.localizedDescription)")
            handleSignInError(error)
        }
    }
    
    /// 处理苹果ID凭证
    private func processAppleIDCredential(_ credential: ASAuthorizationCredential) {
        print("🔵 [Apple ID] 开始处理凭证...")
        guard let appleIDCredential = credential as? ASAuthorizationAppleIDCredential else {
            print("❌ [Apple ID] 凭证类型不匹配")
            showError(message: "无法处理Apple ID凭证")
            return
        }
        
        // 获取用户数据
        let userId = appleIDCredential.user
        let email = appleIDCredential.email ?? ""
        let fullName = [
            appleIDCredential.fullName?.givenName,
            appleIDCredential.fullName?.familyName
        ]
        .compactMap { $0 }
        .joined(separator: " ")
        
        print("ℹ️ [Apple ID] 用户数据 - ID: \(userId), 邮箱: \(email.isEmpty ? "未提供" : email), 姓名: \(fullName.isEmpty ? "未提供" : fullName)")
        
        // 获取身份令牌
        guard let identityTokenData = appleIDCredential.identityToken,
              let identityToken = String(data: identityTokenData, encoding: .utf8) else {
            print("❌ [Apple ID] 无法获取身份令牌")
            showError(message: "无法获取身份令牌")
            return
        }
        
        // 获取授权码（可选）
        var authCode: String? = nil
        if let authCodeData = appleIDCredential.authorizationCode {
            authCode = String(data: authCodeData, encoding: .utf8)
            print("ℹ️ [Apple ID] 获取到授权码")
        } else {
            print("ℹ️ [Apple ID] 未获取到授权码（可选）")
        }
        
        print("🔵 [Apple ID] 准备调用后端认证...")
        authenticateWithBackend(
            userId: userId,
            email: email,
            name: fullName,
            identityToken: identityToken,
            authCode: authCode
        )
    }
    
    // MARK: - 网络操作
    
    /// 与后端服务器进行认证
    private func authenticateWithBackend(
        userId: String,
        email: String,
        name: String,
        identityToken: String,
        authCode: String?
    ) {
        isLoading = true
        print("🔵 [Backend] 开始后端认证...")
        
        let url = "https://your-api-endpoint.com/api/auth/apple"
        var parameters: [String: Any] = [
            "appleUserId": userId,
            "email": email,
            "name": name,
            "identityToken": identityToken
        ]
        
        // 添加授权码（如果存在）
        if let authCode = authCode {
            parameters["authorizationCode"] = authCode
        }
        
        print("📤 [Backend] 请求参数: \(parameters)")
        
        AF.request(url, method: .post, parameters: parameters, encoding: JSONEncoding.default)
            .validate()
            .responseJSON { response in
                self.isLoading = false
                
                switch response.result {
                case .success(let value):
                    print("✅ [Backend] 认证成功: \(value)")
                    self.handleSuccessfulAuthentication()
                case .failure(let error):
                    print("❌ [Backend] 认证失败: \(error.localizedDescription)")
                    if let data = response.data, let json = String(data: data, encoding: .utf8) {
                        print("❌ [Backend] 错误详情: \(json)")
                    }
                    self.handleAuthenticationError(error)
                }
            }
    }
    
    // MARK: - 辅助方法
    
    /// 处理认证成功
    private func handleSuccessfulAuthentication() {
        print("✅ [Auth] 登录成功，准备关闭登录页面...")
        DispatchQueue.main.async {
            self.dismiss()
        }
    }
    
    /// 处理登录错误
    private func handleSignInError(_ error: Error) {
        let errorMessage = (error as NSError).localizedDescription
        print("❌ [Auth] 登录错误: \(errorMessage)")
        showError(message: "登录失败: \(error.localizedDescription)")
    }
    
    /// 处理认证错误
    private func handleAuthenticationError(_ error: AFError) {
        let errorMessage = error.localizedDescription
        print("❌ [Auth] 认证错误: \(errorMessage)")
        showError(message: "登录失败: \(errorMessage)")
    }
    
    /// 显示错误信息
    private func showError(message: String) {
        DispatchQueue.main.async {
            self.errorMessage = message
            self.showError = true
        }
    }
    
    /// 在Safari中打开URL
    private func openURL(_ string: String) {
        guard let url = URL(string: string) else { return }
        UIApplication.shared.open(url)
    }
    
    /// SHA256哈希函数
    private func sha256(_ input: String) -> String {
        let inputData = Data(input.utf8)
        let hashedData = SHA256.hash(data: inputData)
        let hashString = hashedData.compactMap { String(format: "%02x", $0) }.joined()
        return hashString
    }
}

// MARK: - 字符串扩展：生成随机字符串

extension String {
    /// 生成指定长度的随机URL安全字符串
    /// - Parameter length: 字符串长度
    /// - Returns: 随机字符串
    static func randomURLSafeString(length: Int) -> String {
        let characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~"
        var randomString = ""
        
        for _ in 0..<length {
            let randomIndex = Int.random(in: 0..<characters.count)
            let character = characters[characters.index(characters.startIndex, offsetBy: randomIndex)]
            randomString.append(character)
        }
        
        return randomString
    }
}

// MARK: - 预览
struct LoginView_Previews: PreviewProvider {
    static var previews: some View {
        LoginView()
    }
}