/*
Copyright 2013 Google Inc

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

using System.Threading;
using System.Threading.Tasks;

using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Auth.OAuth2.Responses;
using Google.Apis.Auth.OAuth2.Requests;
using Google.Apis.Logging;
using Google.Apis.Util;
using Google.Apis.Util.Store;

namespace Google.Apis.Auth.OAuth2
{
    /// <summary>
    /// Thread-safe OAuth 2.0 authorization code flow for an installed application that persists end-user credentials.
    /// </summary>
    /// <remarks>
    /// Incremental authorization (https://developers.google.com/+/web/api/rest/oauth) is currently not supported
    /// for Installed Apps.
    /// </remarks>
    public class AuthorizationCodeInstalledApp : IAuthorizationCodeInstalledApp
    {
        private static readonly ILogger Logger = ApplicationContext.Logger.ForType<AuthorizationCodeInstalledApp>();

        private readonly IPkceAuthorizationCodeFlow flow;
        private readonly ICodeReceiver codeReceiver;

        /// <summary>
        /// Constructs a new authorization code installed application with the given flow and code receiver.
        /// </summary>
        public AuthorizationCodeInstalledApp(IAuthorizationCodeFlow flow, ICodeReceiver codeReceiver)
        {
            this.flow = flow switch
            {
                IPkceAuthorizationCodeFlow pkceFlow => pkceFlow,
                _ => new NoOpPckeAuthorizationFlow(flow)
            };
            this.codeReceiver = codeReceiver;
        }

        #region IAuthorizationCodeInstalledApp Members

        /// <summary>Gets the authorization code flow.</summary>
        public IAuthorizationCodeFlow Flow
        {
            get { return flow; }
        }

        /// <summary>Gets the code receiver which is responsible for receiving the authorization code.</summary>
        public ICodeReceiver CodeReceiver
        {
            get { return codeReceiver; }
        }

        /// <inheritdoc/>
        public async Task<UserCredential> AuthorizeAsync(string userId, CancellationToken taskCancellationToken)
        {
            // Try to load a token from the data store.
            var token = await Flow.LoadTokenAsync(userId, taskCancellationToken).ConfigureAwait(false);

            // Check if a new authorization code is needed.
            if (ShouldRequestAuthorizationCode(token))
            {
                // Create an authorization code request.
                var redirectUri = CodeReceiver.RedirectUri;
                AuthorizationCodeRequestUrl codeRequest = flow.CreateAuthorizationCodeRequest(redirectUri, out string codeVerifier);

                // Receive the code.
                var response = await CodeReceiver.ReceiveCodeAsync(codeRequest, taskCancellationToken)
                    .ConfigureAwait(false);

                if (string.IsNullOrEmpty(response.Code))
                {
                    var errorResponse = new TokenErrorResponse(response);
                    Logger.Info("Received an error. The response is: {0}", errorResponse);
                    throw new TokenResponseException(errorResponse);
                }

                Logger.Debug("Received \"{0}\" code", response.Code);

                // Get the token based on the code.
                token = await flow.ExchangeCodeForTokenAsync(userId, response.Code, codeVerifier, redirectUri,
                    taskCancellationToken).ConfigureAwait(false);
            }

            return new UserCredential(flow, userId, token);
        }

        /// <summary>
        /// Determines the need for retrieval of a new authorization code, based on the given token and the 
        /// authorization code flow.
        /// </summary>
        public bool ShouldRequestAuthorizationCode(TokenResponse token)
        {
            // TODO: This code should be shared between this class and AuthorizationCodeWebApp.
            // If the flow includes a parameter that requires a new token, if the stored token is null or it doesn't
            // have a refresh token and the access token is expired we need to retrieve a new authorization code.
            return Flow.ShouldForceTokenRetrieval() || token == null || (token.RefreshToken == null 
                && token.ShouldBeRefreshed(flow.Clock));
        }

        #endregion

        /// <summary>
        /// Helper class to wrap non PKCE flows so that <see cref="AuthorizationCodeInstalledApp"/>
        /// does not need to know whether its flow supports PKCE or not.
        /// </summary>
        private class NoOpPckeAuthorizationFlow : IPkceAuthorizationCodeFlow
        {
            private readonly IAuthorizationCodeFlow flow;

            internal NoOpPckeAuthorizationFlow(IAuthorizationCodeFlow flow) => this.flow = flow;

            public IAccessMethod AccessMethod => flow.AccessMethod;

            public IClock Clock => flow.Clock;

            public IDataStore DataStore => flow.DataStore;

            public AuthorizationCodeRequestUrl CreateAuthorizationCodeRequest(string redirectUri, out string codeVerifier)
            {
                // Let's return an invalid codeVerifier just to make certain that it wouldn't be accepted server side
                // if we were to have a bug an include it in the request. But this should never be included in a request.
                codeVerifier = "invalid+*/";
                return flow.CreateAuthorizationCodeRequest(redirectUri);
            }

            public AuthorizationCodeRequestUrl CreateAuthorizationCodeRequest(string redirectUri) =>
                flow.CreateAuthorizationCodeRequest(redirectUri);

            public Task DeleteTokenAsync(string userId, CancellationToken taskCancellationToken) =>
                flow.DeleteTokenAsync(userId, taskCancellationToken);

            public void Dispose() => flow.Dispose();

            public Task<TokenResponse> ExchangeCodeForTokenAsync(string userId, string code, string codeVerifier, string redirectUri, CancellationToken taskCancellationToken) =>
                // We ignore the codeVerifier parameter.
                flow.ExchangeCodeForTokenAsync(userId, code, redirectUri, taskCancellationToken);

            public Task<TokenResponse> ExchangeCodeForTokenAsync(string userId, string code, string redirectUri, CancellationToken taskCancellationToken) =>
                flow.ExchangeCodeForTokenAsync(userId, code, redirectUri, taskCancellationToken);

            public Task<TokenResponse> LoadTokenAsync(string userId, CancellationToken taskCancellationToken) =>
                flow.LoadTokenAsync(userId, taskCancellationToken);

            public Task<TokenResponse> RefreshTokenAsync(string userId, string refreshToken, CancellationToken taskCancellationToken) =>
                flow.RefreshTokenAsync(userId, refreshToken, taskCancellationToken);

            public Task RevokeTokenAsync(string userId, string token, CancellationToken taskCancellationToken) =>
                flow.RevokeTokenAsync(userId, token, taskCancellationToken);

            public bool ShouldForceTokenRetrieval() =>
                flow.ShouldForceTokenRetrieval();
        }
    }
}