import SwiftUI
import AuthenticationServices
import Alamofire
import CryptoKit

/// Main login view that handles Apple Sign In
struct LoginView: View {
    // MARK: - Properties
    @Environment(\.dismiss) private var dismiss
    @State private var isLoading = false
    @State private var showError = false
    @State private var errorMessage = ""
    @State private var currentNonce: String?
    
    // MARK: - Body
    var body: some View {
        ZStack {
            // Background
            Color(.systemBackground)
                .edgesIgnoringSafeArea(.all)
            
            // Main content
            VStack(spacing: 24) {
                Spacer()
                appHeaderView()
                signInButton()
                Spacer()
                termsAndPrivacyView()
            }
            .padding()
            .alert(isPresented: $showError) {
                Alert(
                    title: Text("Error"),
                    message: Text(errorMessage),
                    dismissButton: .default(Text("OK"))
                )
            }
            
            // Loading indicator
            if isLoading {
                loadingView()
            }
        }
        .navigationBarHidden(true)
    }
    
    // MARK: - View Components
    
    /// App header with icon and welcome text
    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)
    }
    
    /// Apple Sign In button
    private func signInButton() -> some View {
        SignInWithAppleButton(
            onRequest: { request in
                // Generate nonce for security
                let nonce = String.randomURLSafeString(length: 32)
                self.currentNonce = nonce
                
                // Configure the request
                request.requestedScopes = [.fullName, .email]
                request.nonce = self.sha256(nonce)
            },
            onCompletion: handleAppleSignIn
        )
        .signInWithAppleButtonStyle(.black)
        .frame(height: 50)
        .padding(.horizontal, 40)
        .cornerRadius(10)
    }
    
    /// Terms and Privacy policy links
    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)
    }
    
    /// Loading overlay view
    private func loadingView() -> some View {
        return ZStack {
            Color.black.opacity(0.4)
                .edgesIgnoringSafeArea(.all)
            
            ProgressView()
                .scaleEffect(1.5)
                .progressViewStyle(CircularProgressViewStyle(tint: .white))
        }
    }
    
    // MARK: - Apple Sign In Handlers
    
    /// Handles the result of Apple Sign In
    private func handleAppleSignIn(result: Result<ASAuthorization, Error>) {
        switch result {
        case .success(let authResults):
            processAppleIDCredential(authResults.credential)
        case .failure(let error):
            handleSignInError(error)
        }
    }
    
    /// Processes the Apple ID credential
    private func processAppleIDCredential(_ credential: ASAuthorizationCredential) {
        guard let appleIDCredential = credential as? ASAuthorizationAppleIDCredential else {
            showError(message: "Unable to process Apple ID credentials")
            return
        }
        
        // Get user data
        let userId = appleIDCredential.user
        let email = appleIDCredential.email ?? ""
        let fullName = [
            appleIDCredential.fullName?.givenName,
            appleIDCredential.fullName?.familyName
        ]
        .compactMap { $0 }
        .joined(separator: " ")
        
        // Get the identity token
        guard let identityTokenData = appleIDCredential.identityToken,
              let identityToken = String(data: identityTokenData, encoding: .utf8) else {
            showError(message: "Unable to fetch identity token")
            return
        }
        
        // Get the authorization code (optional)
        var authCode: String? = nil
        if let authCodeData = appleIDCredential.authorizationCode {
            authCode = String(data: authCodeData, encoding: .utf8)
        }
        
        // Proceed with backend authentication
        authenticateWithBackend(
            userId: userId,
            email: email,
            name: fullName,
            identityToken: identityToken,
            authCode: authCode
        )
    }
    
    // MARK: - Network Operations
    
    /// Authenticates the user with the backend server
    private func authenticateWithBackend(
        userId: String,
        email: String,
        name: String,
        identityToken: String,
        authCode: String?
    ) {
        isLoading = true
        
        let url = "https://your-api-endpoint.com/api/auth/apple"
        var parameters: [String: Any] = [
            "appleUserId": userId,
            "email": email,
            "name": name,
            "identityToken": identityToken
        ]
        
        // Add authorization code if available
        if let authCode = authCode {
            parameters["authorizationCode"] = authCode
        }
        
        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("Authentication successful: \(value)")
                    self.handleSuccessfulAuthentication()
                case .failure(let error):
                    self.handleAuthenticationError(error)
                }
            }
    }
    
    // MARK: - Helper Methods
    
    /// Handles successful authentication
    private func handleSuccessfulAuthentication() {
        DispatchQueue.main.async {
            self.dismiss()
        }
    }
    
    /// Handles sign in errors
    private func handleSignInError(_ error: Error) {
        let errorMessage = (error as NSError).localizedDescription
        print("Apple Sign In failed: \(errorMessage)")
        showError(message: "Sign in failed: \(error.localizedDescription)")
    }
    
    /// Handles authentication errors
    private func handleAuthenticationError(_ error: AFError) {
        let errorMessage = error.localizedDescription
        print("API Error: \(errorMessage)")
        showError(message: "Failed to sign in: \(errorMessage)")
    }
    
    /// Shows error message to the user
    private func showError(message: String) {
        DispatchQueue.main.async {
            self.errorMessage = message
            self.showError = true
        }
    }
    
    /// Opens a URL in Safari
    private func openURL(_ string: String) {
        guard let url = URL(string: string) else { return }
        UIApplication.shared.open(url)
    }
    
    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: - String Extension for Random String Generation

extension String {
    /// Generates a random string of the specified length using URL-safe characters
    /// - Parameter length: The length of the random string to generate
    /// - Returns: A random string containing URL-safe characters
    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: - Preview
struct LoginView_Previews: PreviewProvider {
    static var previews: some View {
        LoginView()
    }
}