// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Security.Cryptography;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features.Authentication;
using Microsoft.AspNetCore.Http.Authentication;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNetCore.Authentication
{
    public abstract class RemoteAuthenticationHandler<TOptions> : AuthenticationHandler<TOptions> where TOptions : RemoteAuthenticationOptions
    {
        private const string CorrelationPrefix = ".AspNetCore.Correlation.";
        private const string CorrelationProperty = ".xsrf";
        private const string CorrelationMarker = "N";
        private const string AuthSchemeKey = ".AuthScheme";

        private static readonly RandomNumberGenerator CryptoRandom = RandomNumberGenerator.Create();

        public override async Task<bool> HandleRequestAsync()
        {
            if (Options.CallbackPath == Request.Path)
            {
                return await HandleRemoteCallbackAsync();
            }

            return false;
        }

        protected virtual async Task<bool> HandleRemoteCallbackAsync()
        {
            AuthenticationTicket ticket = null;
            Exception exception = null;

            try
            {
                var authResult = await HandleRemoteAuthenticateAsync();
                if (authResult == null)
                {
                    exception = new InvalidOperationException("Invalid return state, unable to redirect.");
                }
                else if (authResult.Handled)
                {
                    return true;
                }
                else if (authResult.Skipped)
                {
                    return false;
                }
                else if (!authResult.Succeeded)
                {
                    exception = authResult.Failure ??
                                new InvalidOperationException("Invalid return state, unable to redirect.");
                }

                ticket = authResult.Ticket;
            }
            catch (Exception ex)
            {
                exception = ex;
            }

            if (exception != null)
            {
                Logger.RemoteAuthenticationError(exception.Message);
                var errorContext = new FailureContext(Context, exception);
                await Options.Events.RemoteFailure(errorContext);

                if (errorContext.HandledResponse)
                {
                    return true;
                }

                if (errorContext.Skipped)
                {
                    return false;
                }

                throw new AggregateException("Unhandled remote failure.", exception);
            }

            // We have a ticket if we get here
            var context = new TicketReceivedContext(Context, Options, ticket)
            {
                ReturnUri = ticket.Properties.RedirectUri,
            };
            // REVIEW: is this safe or good?
            ticket.Properties.RedirectUri = null;

            // Mark which provider produced this identity so we can cross-check later in HandleAuthenticateAsync
            context.Properties.Items[AuthSchemeKey] = Options.AuthenticationScheme;

            await Options.Events.TicketReceived(context);

            if (context.HandledResponse)
            {
                Logger.SigninHandled();
                return true;
            }
            else if (context.Skipped)
            {
                Logger.SigninSkipped();
                return false;
            }

            await Context.Authentication.SignInAsync(Options.SignInScheme, context.Principal, context.Properties);

            // Default redirect path is the base path
            if (string.IsNullOrEmpty(context.ReturnUri))
            {
                context.ReturnUri = "/";
            }

            Response.Redirect(context.ReturnUri);
            return true;
        }

        /// <summary>
        /// Authenticate the user identity with the identity provider.
        ///
        /// The method process the request on the endpoint defined by CallbackPath.
        /// </summary>
        protected abstract Task<AuthenticateResult> HandleRemoteAuthenticateAsync();

        protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
        {
            // Most RemoteAuthenticationHandlers will have a PriorHandler, but it might not be set up during unit tests.
            if (PriorHandler != null)
            {
                var authenticateContext = new AuthenticateContext(Options.SignInScheme);
                await PriorHandler.AuthenticateAsync(authenticateContext);
                if (authenticateContext.Accepted)
                {
                    if (authenticateContext.Error != null)
                    {
                        return AuthenticateResult.Fail(authenticateContext.Error);
                    }

                    // The SignInScheme may be shared with multiple providers, make sure this middleware issued the identity.
                    string authenticatedScheme;
                    if (authenticateContext.Principal != null && authenticateContext.Properties != null
                        && authenticateContext.Properties.TryGetValue(AuthSchemeKey, out authenticatedScheme)
                        && string.Equals(Options.AuthenticationScheme, authenticatedScheme, StringComparison.Ordinal))
                    {
                        return AuthenticateResult.Success(new AuthenticationTicket(authenticateContext.Principal,
                            new AuthenticationProperties(authenticateContext.Properties), Options.AuthenticationScheme));
                    }

                    return AuthenticateResult.Fail("Not authenticated");
                }

            }

            return AuthenticateResult.Fail("Remote authentication does not directly support authenticate");
        }

        protected override Task HandleSignOutAsync(SignOutContext context)
        {
            throw new NotSupportedException();
        }

        protected override Task HandleSignInAsync(SignInContext context)
        {
            throw new NotSupportedException();
        }

        protected override async Task<bool> HandleForbiddenAsync(ChallengeContext context)
        {
            var challengeContext = new ChallengeContext(Options.SignInScheme, context.Properties, ChallengeBehavior.Forbidden);
            await PriorHandler.ChallengeAsync(challengeContext);
            return challengeContext.Accepted;
        }

        protected virtual void GenerateCorrelationId(AuthenticationProperties properties)
        {
            if (properties == null)
            {
                throw new ArgumentNullException(nameof(properties));
            }

            var bytes = new byte[32];
            CryptoRandom.GetBytes(bytes);
            var correlationId = Base64UrlTextEncoder.Encode(bytes);

            var cookieOptions = new CookieOptions
            {
                HttpOnly = true,
                Secure = Request.IsHttps,
                Expires = Options.SystemClock.UtcNow.Add(Options.RemoteAuthenticationTimeout),
            };

            properties.Items[CorrelationProperty] = correlationId;

            var cookieName = CorrelationPrefix + Options.AuthenticationScheme + "." + correlationId;

            Response.Cookies.Append(cookieName, CorrelationMarker, cookieOptions);
        }

        protected virtual bool ValidateCorrelationId(AuthenticationProperties properties)
        {
            if (properties == null)
            {
                throw new ArgumentNullException(nameof(properties));
            }

            string correlationId;
            if (!properties.Items.TryGetValue(CorrelationProperty, out correlationId))
            {
                Logger.CorrelationPropertyNotFound(CorrelationPrefix);
                return false;
            }

            properties.Items.Remove(CorrelationProperty);

            var cookieName = CorrelationPrefix + Options.AuthenticationScheme + "." + correlationId;

            var correlationCookie = Request.Cookies[cookieName];
            if (string.IsNullOrEmpty(correlationCookie))
            {
                Logger.CorrelationCookieNotFound(cookieName);
                return false;
            }

            var cookieOptions = new CookieOptions
            {
                HttpOnly = true,
                Secure = Request.IsHttps
            };
            Response.Cookies.Delete(cookieName, cookieOptions);

            if (!string.Equals(correlationCookie, CorrelationMarker, StringComparison.Ordinal))
            {
                Logger.UnexpectedCorrelationCookieValue(cookieName, correlationCookie);
                return false;
            }

            return true;
        }
    }
}