// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

import Foundation
import AuthenticationServices
import Combine
import SafariServices

/// Manages the sign in/sign out process using `ASWebAuthenticationSession`.
class HostedUIFlow: NSObject, ASWebAuthenticationPresentationContextProviding {
    
    /// Launches `url` in an `ASWebAuthenticationSession`.
    ///
    /// `url` is either the signin or signout URL.
    @MainActor public func launchUrl(
        _ url: String,
        callbackURLScheme: String,
        preferPrivateSession: Bool
    ) async throws -> [String: String] {
        guard let uri = URL(string: url) else {
            throw HostedUIError.unknown("Invalid URL: \(url)")
        }
        return try await withCheckedThrowingContinuation { continuation in
            let session = ASWebAuthenticationSession(url: uri, callbackURLScheme: callbackURLScheme) {
                callbackURL, error in
                if let error = error {
                    continuation.resume(throwing: HostedUIError.fromError(error))
                    return
                }
                guard let callbackURL = callbackURL else {
                    continuation.resume(throwing: HostedUIError.unknown("Nil callback URL"))
                    return
                }
                let queryParameters = HostedUIFlow.processParameters(callbackURL)
                continuation.resume(returning: queryParameters)
            }

            session.presentationContextProvider = self
            session.prefersEphemeralWebBrowserSession = preferPrivateSession
            session.start()
        }
    }

    func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
        return ASPresentationAnchor()
    }

    /// Collects the query parameters returned in `callbackURL`.
    static private func processParameters(_ callbackURL: URL) -> [String: String] {
        let urlComponents = URLComponents(string: callbackURL.absoluteString)
        guard let queryItems = urlComponents?.queryItems else {
            return [:]
        }
        var queryParameters: [String: String] = [:]
        for queryItem in queryItems {
            queryParameters[queryItem.name] = queryItem.value ?? ""
        }
        return queryParameters
    }
    
}