// 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.Collections.Generic;
using System.Globalization;
using System.Net.Http;
using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNet.Http;
using Microsoft.AspNet.Http.Authentication;
using Microsoft.AspNet.Http.Features.Authentication;
using Microsoft.AspNet.Http.Internal;
using Microsoft.AspNet.WebUtilities;
using Microsoft.Framework.Internal;
using Microsoft.Framework.Logging;

namespace Microsoft.AspNet.Authentication.Twitter
{
    internal class TwitterAuthenticationHandler : AuthenticationHandler<TwitterAuthenticationOptions>
    {
        private static readonly DateTime Epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
        private const string StateCookie = "__TwitterState";
        private const string RequestTokenEndpoint = "https://api.twitter.com/oauth/request_token";
        private const string AuthenticationEndpoint = "https://twitter.com/oauth/authenticate?oauth_token=";
        private const string AccessTokenEndpoint = "https://api.twitter.com/oauth/access_token";

        private readonly HttpClient _httpClient;

        public TwitterAuthenticationHandler(HttpClient httpClient)
        {
            _httpClient = httpClient;
        }

        public override async Task<bool> InvokeAsync()
        {
            if (Options.CallbackPath.HasValue && Options.CallbackPath == Request.Path)
            {
                return await InvokeReturnPathAsync();
            }
            return false;
        }

        protected override async Task<AuthenticationTicket> HandleAuthenticateAsync()
        {
            AuthenticationProperties properties = null;
            try
            {
                var query = Request.Query;
                var protectedRequestToken = Request.Cookies[StateCookie];

                var requestToken = Options.StateDataFormat.Unprotect(protectedRequestToken);

                if (requestToken == null)
                {
                    Logger.LogWarning("Invalid state");
                    return null;
                }

                properties = requestToken.Properties;

                var returnedToken = query.Get("oauth_token");
                if (string.IsNullOrWhiteSpace(returnedToken))
                {
                    Logger.LogWarning("Missing oauth_token");
                    return new AuthenticationTicket(properties, Options.AuthenticationScheme);
                }

                if (returnedToken != requestToken.Token)
                {
                    Logger.LogWarning("Unmatched token");
                    return new AuthenticationTicket(properties, Options.AuthenticationScheme);
                }

                var oauthVerifier = query.Get("oauth_verifier");
                if (string.IsNullOrWhiteSpace(oauthVerifier))
                {
                    Logger.LogWarning("Missing or blank oauth_verifier");
                    return new AuthenticationTicket(properties, Options.AuthenticationScheme);
                }

                var cookieOptions = new CookieOptions
                {
                    HttpOnly = true,
                    Secure = Request.IsHttps
                };

                Response.Cookies.Delete(StateCookie, cookieOptions);

                var accessToken = await ObtainAccessTokenAsync(Options.ConsumerKey, Options.ConsumerSecret, requestToken, oauthVerifier);
                
                var identity = new ClaimsIdentity(new[]
                {
                    new Claim(ClaimTypes.NameIdentifier, accessToken.UserId, ClaimValueTypes.String, Options.ClaimsIssuer),
                    new Claim(ClaimTypes.Name, accessToken.ScreenName, ClaimValueTypes.String, Options.ClaimsIssuer),
                    new Claim("urn:twitter:userid", accessToken.UserId, ClaimValueTypes.String, Options.ClaimsIssuer),
                    new Claim("urn:twitter:screenname", accessToken.ScreenName, ClaimValueTypes.String, Options.ClaimsIssuer)
                },
                Options.ClaimsIssuer);

                if (Options.SaveTokensAsClaims)
                {
                    identity.AddClaim(new Claim("access_token", accessToken.Token, ClaimValueTypes.String, Options.ClaimsIssuer));
                }
                
                return await CreateTicketAsync(identity, properties, accessToken);
            }
            catch (Exception ex)
            {
                Logger.LogError("Authentication failed", ex);
                return new AuthenticationTicket(properties, Options.AuthenticationScheme);
            }
        }

        protected virtual async Task<AuthenticationTicket> CreateTicketAsync(ClaimsIdentity identity, AuthenticationProperties properties, AccessToken token)
        {
            var notification = new TwitterAuthenticatedContext(Context, token.UserId, token.ScreenName, token.Token, token.TokenSecret)
            {
                Principal = new ClaimsPrincipal(identity),
                Properties = properties
            };

            await Options.Notifications.Authenticated(notification);
            
            if (notification.Principal?.Identity == null)
            {
                return null;
            }

            return new AuthenticationTicket(notification.Principal, notification.Properties, Options.AuthenticationScheme);
        }

        protected override async Task<bool> HandleUnauthorizedAsync([NotNull] ChallengeContext context)
        {
            var properties = new AuthenticationProperties(context.Properties);
            if (string.IsNullOrEmpty(properties.RedirectUri))
            {
                properties.RedirectUri = CurrentUri;
            }

            var requestToken = await ObtainRequestTokenAsync(Options.ConsumerKey, Options.ConsumerSecret, BuildRedirectUri(Options.CallbackPath), properties);
            if (requestToken.CallbackConfirmed)
            {
                var twitterAuthenticationEndpoint = AuthenticationEndpoint + requestToken.Token;

                var cookieOptions = new CookieOptions
                {
                    HttpOnly = true,
                    Secure = Request.IsHttps
                };

                Response.Cookies.Append(StateCookie, Options.StateDataFormat.Protect(requestToken), cookieOptions);

                var redirectContext = new TwitterApplyRedirectContext(
                    Context, Options,
                    properties, twitterAuthenticationEndpoint);
                Options.Notifications.ApplyRedirect(redirectContext);
                return true;
            }
            else
            {
                Logger.LogError("requestToken CallbackConfirmed!=true");
            }
            return false; // REVIEW: Make sure this should not stop other handlers
        }

        public async Task<bool> InvokeReturnPathAsync()
        {
            var model = await HandleAuthenticateOnceAsync();
            if (model == null)
            {
                Logger.LogWarning("Invalid return state, unable to redirect.");
                Response.StatusCode = 500;
                return true;
            }

            var context = new TwitterReturnEndpointContext(Context, model)
            {
                SignInScheme = Options.SignInScheme,
                RedirectUri = model.Properties.RedirectUri
            };
            model.Properties.RedirectUri = null;

            await Options.Notifications.ReturnEndpoint(context);

            if (context.SignInScheme != null && context.Principal != null)
            {
                await Context.Authentication.SignInAsync(context.SignInScheme, context.Principal, context.Properties);
            }

            if (!context.IsRequestCompleted && context.RedirectUri != null)
            {
                if (context.Principal == null)
                {
                    // add a redirect hint that sign-in failed in some way
                    context.RedirectUri = QueryHelpers.AddQueryString(context.RedirectUri, "error", "access_denied");
                }
                Response.Redirect(context.RedirectUri);
                context.RequestCompleted();
            }

            return context.IsRequestCompleted;
        }

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

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

        protected override Task<bool> HandleForbiddenAsync(ChallengeContext context)
        {
            throw new NotSupportedException();
        }

        private async Task<RequestToken> ObtainRequestTokenAsync(string consumerKey, string consumerSecret, string callBackUri, AuthenticationProperties properties)
        {
            Logger.LogVerbose("ObtainRequestToken");

            var nonce = Guid.NewGuid().ToString("N");

            var authorizationParts = new SortedDictionary<string, string>
            {
                { "oauth_callback", callBackUri },
                { "oauth_consumer_key", consumerKey },
                { "oauth_nonce", nonce },
                { "oauth_signature_method", "HMAC-SHA1" },
                { "oauth_timestamp", GenerateTimeStamp() },
                { "oauth_version", "1.0" }
            };

            var parameterBuilder = new StringBuilder();
            foreach (var authorizationKey in authorizationParts)
            {
                parameterBuilder.AppendFormat("{0}={1}&", UrlEncoder.UrlEncode(authorizationKey.Key), UrlEncoder.UrlEncode(authorizationKey.Value));
            }
            parameterBuilder.Length--;
            var parameterString = parameterBuilder.ToString();

            var canonicalizedRequestBuilder = new StringBuilder();
            canonicalizedRequestBuilder.Append(HttpMethod.Post.Method);
            canonicalizedRequestBuilder.Append("&");
            canonicalizedRequestBuilder.Append(UrlEncoder.UrlEncode(RequestTokenEndpoint));
            canonicalizedRequestBuilder.Append("&");
            canonicalizedRequestBuilder.Append(UrlEncoder.UrlEncode(parameterString));

            var signature = ComputeSignature(consumerSecret, null, canonicalizedRequestBuilder.ToString());
            authorizationParts.Add("oauth_signature", signature);

            var authorizationHeaderBuilder = new StringBuilder();
            authorizationHeaderBuilder.Append("OAuth ");
            foreach (var authorizationPart in authorizationParts)
            {
                authorizationHeaderBuilder.AppendFormat(
                    "{0}=\"{1}\", ", authorizationPart.Key, UrlEncoder.UrlEncode(authorizationPart.Value));
            }
            authorizationHeaderBuilder.Length = authorizationHeaderBuilder.Length - 2;

            var request = new HttpRequestMessage(HttpMethod.Post, RequestTokenEndpoint);
            request.Headers.Add("Authorization", authorizationHeaderBuilder.ToString());

            var response = await _httpClient.SendAsync(request, Context.RequestAborted);
            response.EnsureSuccessStatusCode();
            string responseText = await response.Content.ReadAsStringAsync();

            var responseParameters = new FormCollection(FormReader.ReadForm(responseText));
            if (string.Equals(responseParameters["oauth_callback_confirmed"], "true", StringComparison.Ordinal))
            {
                return new RequestToken { Token = Uri.UnescapeDataString(responseParameters["oauth_token"]), TokenSecret = Uri.UnescapeDataString(responseParameters["oauth_token_secret"]), CallbackConfirmed = true, Properties = properties };
            }

            return new RequestToken();
        }

        private async Task<AccessToken> ObtainAccessTokenAsync(string consumerKey, string consumerSecret, RequestToken token, string verifier)
        {
            // https://dev.twitter.com/docs/api/1/post/oauth/access_token

            Logger.LogVerbose("ObtainAccessToken");

            var nonce = Guid.NewGuid().ToString("N");

            var authorizationParts = new SortedDictionary<string, string>
            {
                { "oauth_consumer_key", consumerKey },
                { "oauth_nonce", nonce },
                { "oauth_signature_method", "HMAC-SHA1" },
                { "oauth_token", token.Token },
                { "oauth_timestamp", GenerateTimeStamp() },
                { "oauth_verifier", verifier },
                { "oauth_version", "1.0" },
            };

            var parameterBuilder = new StringBuilder();
            foreach (var authorizationKey in authorizationParts)
            {
                parameterBuilder.AppendFormat("{0}={1}&", UrlEncoder.UrlEncode(authorizationKey.Key), UrlEncoder.UrlEncode(authorizationKey.Value));
            }
            parameterBuilder.Length--;
            var parameterString = parameterBuilder.ToString();

            var canonicalizedRequestBuilder = new StringBuilder();
            canonicalizedRequestBuilder.Append(HttpMethod.Post.Method);
            canonicalizedRequestBuilder.Append("&");
            canonicalizedRequestBuilder.Append(UrlEncoder.UrlEncode(AccessTokenEndpoint));
            canonicalizedRequestBuilder.Append("&");
            canonicalizedRequestBuilder.Append(UrlEncoder.UrlEncode(parameterString));

            var signature = ComputeSignature(consumerSecret, token.TokenSecret, canonicalizedRequestBuilder.ToString());
            authorizationParts.Add("oauth_signature", signature);
            authorizationParts.Remove("oauth_verifier");

            var authorizationHeaderBuilder = new StringBuilder();
            authorizationHeaderBuilder.Append("OAuth ");
            foreach (var authorizationPart in authorizationParts)
            {
                authorizationHeaderBuilder.AppendFormat(
                    "{0}=\"{1}\", ", authorizationPart.Key, UrlEncoder.UrlEncode(authorizationPart.Value));
            }
            authorizationHeaderBuilder.Length = authorizationHeaderBuilder.Length - 2;

            var request = new HttpRequestMessage(HttpMethod.Post, AccessTokenEndpoint);
            request.Headers.Add("Authorization", authorizationHeaderBuilder.ToString());

            var formPairs = new Dictionary<string, string>()
            {
                { "oauth_verifier", verifier },
            };

            request.Content = new FormUrlEncodedContent(formPairs);

            var response = await _httpClient.SendAsync(request, Context.RequestAborted);

            if (!response.IsSuccessStatusCode)
            {
                Logger.LogError("AccessToken request failed with a status code of " + response.StatusCode);
                response.EnsureSuccessStatusCode(); // throw
            }

            var responseText = await response.Content.ReadAsStringAsync();
            var responseParameters = new FormCollection(FormReader.ReadForm(responseText));

            return new AccessToken
            {
                Token = Uri.UnescapeDataString(responseParameters["oauth_token"]),
                TokenSecret = Uri.UnescapeDataString(responseParameters["oauth_token_secret"]),
                UserId = Uri.UnescapeDataString(responseParameters["user_id"]),
                ScreenName = Uri.UnescapeDataString(responseParameters["screen_name"])
            };
        }

        private static string GenerateTimeStamp()
        {
            var secondsSinceUnixEpocStart = DateTime.UtcNow - Epoch;
            return Convert.ToInt64(secondsSinceUnixEpocStart.TotalSeconds).ToString(CultureInfo.InvariantCulture);
        }

        private string ComputeSignature(string consumerSecret, string tokenSecret, string signatureData)
        {
            using (var algorithm = new HMACSHA1())
            {
                algorithm.Key = Encoding.ASCII.GetBytes(
                    string.Format(CultureInfo.InvariantCulture,
                        "{0}&{1}",
                        UrlEncoder.UrlEncode(consumerSecret),
                        string.IsNullOrEmpty(tokenSecret) ? string.Empty : UrlEncoder.UrlEncode(tokenSecret)));
                var hash = algorithm.ComputeHash(Encoding.ASCII.GetBytes(signatureData));
                return Convert.ToBase64String(hash);
            }
        }
    }
}