// 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.Globalization;
using System.Net.Http;
using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNet.Authentication.OAuth;
using Microsoft.AspNet.Builder;
using Microsoft.AspNet.Http.Authentication;
using Microsoft.AspNet.WebUtilities;
using Newtonsoft.Json.Linq;

namespace Microsoft.AspNet.Authentication.Facebook
{
    internal class FacebookHandler : OAuthHandler<FacebookOptions>
    {
        public FacebookHandler(HttpClient httpClient)
            : base(httpClient)
        {
        }

        protected override async Task<AuthenticationTicket> CreateTicketAsync(ClaimsIdentity identity, AuthenticationProperties properties, OAuthTokenResponse tokens)
        {
            var endpoint = QueryHelpers.AddQueryString(Options.UserInformationEndpoint, "access_token", tokens.AccessToken);
            if (Options.SendAppSecretProof)
            {
                endpoint = QueryHelpers.AddQueryString(endpoint, "appsecret_proof", GenerateAppSecretProof(tokens.AccessToken));
            }
            if (Options.Fields.Count > 0)
            {
                endpoint = QueryHelpers.AddQueryString(endpoint, "fields", string.Join(",", Options.Fields));
            }

            var response = await Backchannel.GetAsync(endpoint, Context.RequestAborted);
            response.EnsureSuccessStatusCode();

            var payload = JObject.Parse(await response.Content.ReadAsStringAsync());

            var ticket = new AuthenticationTicket(new ClaimsPrincipal(identity), properties, Options.AuthenticationScheme);
            var context = new OAuthCreatingTicketContext(ticket, Context, Options, Backchannel, tokens, payload);

            var identifier = FacebookHelper.GetId(payload);
            if (!string.IsNullOrEmpty(identifier))
            {
                identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, identifier, ClaimValueTypes.String, Options.ClaimsIssuer));
            }

            var userName = FacebookHelper.GetUserName(payload);
            if (!string.IsNullOrEmpty(userName))
            {
                identity.AddClaim(new Claim(ClaimsIdentity.DefaultNameClaimType, userName, ClaimValueTypes.String, Options.ClaimsIssuer));
            }

            var email = FacebookHelper.GetEmail(payload);
            if (!string.IsNullOrEmpty(email))
            {
                identity.AddClaim(new Claim(ClaimTypes.Email, email, ClaimValueTypes.String, Options.ClaimsIssuer));
            }

            var name = FacebookHelper.GetName(payload);
            if (!string.IsNullOrEmpty(name))
            {
                identity.AddClaim(new Claim("urn:facebook:name", name, ClaimValueTypes.String, Options.ClaimsIssuer));

                // Many Facebook accounts do not set the UserName field.  Fall back to the Name field instead.
                if (string.IsNullOrEmpty(userName))
                {
                    identity.AddClaim(new Claim(identity.NameClaimType, name, ClaimValueTypes.String, Options.ClaimsIssuer));
                }
            }

            var link = FacebookHelper.GetLink(payload);
            if (!string.IsNullOrEmpty(link))
            {
                identity.AddClaim(new Claim("urn:facebook:link", link, ClaimValueTypes.String, Options.ClaimsIssuer));
            }

            await Options.Events.CreatingTicket(context);

            return context.Ticket;
        }

        private string GenerateAppSecretProof(string accessToken)
        {
            using (var algorithm = new HMACSHA256(Encoding.ASCII.GetBytes(Options.AppSecret)))
            {
                var hash = algorithm.ComputeHash(Encoding.ASCII.GetBytes(accessToken));
                var builder = new StringBuilder();
                for (int i = 0; i < hash.Length; i++)
                {
                    builder.Append(hash[i].ToString("x2", CultureInfo.InvariantCulture));
                }
                return builder.ToString();
            }
        }

        protected override string FormatScope()
        {
            // Facebook deviates from the OAuth spec here. They require comma separated instead of space separated.
            // https://developers.facebook.com/docs/reference/dialogs/oauth
            // http://tools.ietf.org/html/rfc6749#section-3.3
            return string.Join(",", Options.Scope);
        }
    }
}