using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
using BirdsiteLive.ActivityPub;
using BirdsiteLive.ActivityPub.Converters;
using BirdsiteLive.ActivityPub.Models;
using BirdsiteLive.Common.Regexes;
using BirdsiteLive.Common.Settings;
using BirdsiteLive.Cryptography;
using BirdsiteLive.DAL.Contracts;
using BirdsiteLive.DAL.Models;
using BirdsiteLive.Domain.BusinessUseCases;
using BirdsiteLive.Domain.Repository;
using BirdsiteLive.Domain.Statistics;
using BirdsiteLive.Domain.Tools;
using BirdsiteLive.Twitter;
using BirdsiteLive.Twitter.Models;
using Tweetinvi.Core.Exceptions;
using Tweetinvi.Models;

namespace BirdsiteLive.Domain
{
    public interface IUserService
    {
        Actor GetUser(TwitterUser twitterUser, SyncTwitterUser dbTwitterUser);
        Task<bool> FollowRequestedAsync(string signature, string method, string path, string queryString, Dictionary<string, string> requestHeaders, ActivityFollow activity, string body);
        Task<bool> UndoFollowRequestedAsync(string signature, string method, string path, string queryString, Dictionary<string, string> requestHeaders, ActivityUndoFollow activity, string body);

        Task<bool> SendRejectFollowAsync(ActivityFollow activity, string followerHost);
        Task<bool> DeleteRequestedAsync(string signature, string method, string path, string queryString, Dictionary<string, string> requestHeaders, ActivityDelete activity, string body);
    }

    public class UserService : IUserService
    {
        private readonly IProcessDeleteUser _processDeleteUser;
        private readonly IProcessFollowUser _processFollowUser;
        private readonly IProcessUndoFollowUser _processUndoFollowUser;

        private readonly InstanceSettings _instanceSettings;
        private readonly ICryptoService _cryptoService;
        private readonly IActivityPubService _activityPubService;
        private readonly IStatusExtractor _statusExtractor;
        private readonly IExtractionStatisticsHandler _statisticsHandler;

        private readonly ITwitterUserService _twitterUserService;

        private readonly IModerationRepository _moderationRepository;

        private readonly IFollowersDal _followerDal;

        #region Ctor
        public UserService(InstanceSettings instanceSettings, ICryptoService cryptoService, IActivityPubService activityPubService, IProcessFollowUser processFollowUser, IProcessUndoFollowUser processUndoFollowUser, IStatusExtractor statusExtractor, IExtractionStatisticsHandler statisticsHandler, ITwitterUserService twitterUserService, IModerationRepository moderationRepository, IFollowersDal followerDal, IProcessDeleteUser processDeleteUser)
        {
            _instanceSettings = instanceSettings;
            _cryptoService = cryptoService;
            _activityPubService = activityPubService;
            _processFollowUser = processFollowUser;
            _processUndoFollowUser = processUndoFollowUser;
            _statusExtractor = statusExtractor;
            _statisticsHandler = statisticsHandler;
            _twitterUserService = twitterUserService;
            _moderationRepository = moderationRepository;
            _followerDal = followerDal;
            _processDeleteUser = processDeleteUser;
        }
        #endregion

        public Actor GetUser(TwitterUser twitterUser, SyncTwitterUser dbTwitterUser)
        {
            var actorUrl = UrlFactory.GetActorUrl(_instanceSettings.Domain, twitterUser.Acct);
            var acct = twitterUser.Acct.ToLowerInvariant();

            // Extract links, mentions, etc
            var description = twitterUser.Description;
            if (!string.IsNullOrWhiteSpace(description))
            {
                var extracted = _statusExtractor.Extract(description, _instanceSettings.ResolveMentionsInProfiles);
                description = extracted.content;

                _statisticsHandler.ExtractedDescription(extracted.tags.Count(x => x.type == "Mention"));
            }

            var attachments = new List<UserAttachment>();
            attachments.Add(new UserAttachment
            {
                type = "PropertyValue",
                name = _instanceSettings.TwitterDomainLabel != "" ? _instanceSettings.TwitterDomainLabel : _instanceSettings.TwitterDomain,
                value = $"<a href=\"https://{_instanceSettings.TwitterDomain}/{acct}\" rel=\"me nofollow noopener noreferrer\" target=\"_blank\"><span class=\"invisible\">https://</span><span class=\"ellipsis\">{_instanceSettings.TwitterDomain}/{acct}</span></a>"
            });

            if(_instanceSettings.TwitterDomain != "twitter.com")
            {
                attachments.Add(new UserAttachment
                {
                    type = "PropertyValue",
                    name = "Twitter",
                    value = $"twitter.com/{acct}"
                });
            }

            if (_instanceSettings.ShowAboutInstanceOnProfiles)
            {
                attachments.Add(new UserAttachment
                {
                    type = "PropertyValue",
                    name = $"About {_instanceSettings.Name}",
                    value = $"<a href=\"https://{_instanceSettings.Domain}/About\" rel=\"nofollow noopener noreferrer\" target=\"_blank\"><span class=\"invisible\">https://</span><span class=\"ellipsis\">{_instanceSettings.Domain}/About</span></a>"
                });
            }

            var user = new Actor
            {
                id = actorUrl,
                type = "Service", 
                followers = $"{actorUrl}/followers",
                preferredUsername = acct,
                name = twitterUser.Name,
                inbox = $"{actorUrl}/inbox",
                summary = "[UNOFFICIAL MIRROR: This is a view of Twitter using ActivityPub]<br/><br/>" + description,
                url = actorUrl,
                manuallyApprovesFollowers = twitterUser.Protected,
                discoverable = false,
                publicKey = new PublicKey()
                {
                    id = $"{actorUrl}#main-key",
                    owner = actorUrl,
                    publicKeyPem = _cryptoService.GetUserPem(acct)
                },
                icon = new Image
                {
                    mediaType = "image/jpeg",
                    url = twitterUser.ProfileImageUrl
                },
                image = new Image
                {
                    mediaType = "image/jpeg",
                    url = twitterUser.ProfileBannerURL
                },
                attachment = new []
                {
                    new UserAttachment
                    {
                        type = "PropertyValue",
                        name = "Official Account",
                        value = $"<a href=\"https://twitter.com/{acct}\" rel=\"me nofollow noopener noreferrer\" target=\"_blank\"><span class=\"invisible\">https://</span><span class=\"ellipsis\">twitter.com/{acct}</span></a>"
                    },
                    new UserAttachment
                    {
                        type = "PropertyValue",
                        name = "Disclaimer",
                        value = "This is an automatically created and managed mirror profile from Twitter. While it reflects exactly the content of the original account, it doesn't provide support for interactions and replies. It is an equivalent view from other 3rd party Twitter client apps and uses the same technical means to provide it."
                    },
                    new UserAttachment
                    {
                        type = "PropertyValue",
                        name = "Take control of this account",
                        value = $"<a href=\"https://{_instanceSettings.Domain}/migration/move/{acct}\" rel=\"me nofollow noopener noreferrer\" target=\"_blank\">MANAGE</a>"
                    }
                },
                endpoints = new EndPoints
                {
                    sharedInbox = $"https://{_instanceSettings.Domain}/inbox"
                },
                movedTo = dbTwitterUser?.MovedTo
            };

            if (twitterUser.Verified)
            {
                user.tag = new List<Tag>
                {
                    new Tag
                    {
                        icon = new TagResource
                        {
                            type = "Image",
                            url = "https://" + _instanceSettings.Domain + "/verified.png"
                        },
                        id = "https://" + _instanceSettings.Domain + "/verified.png",
                        name = ":verified:",
                        type = "Emoji"
                    }
                };

                user.name += " :verified:";
            }

            return user;
        }

        public async Task<bool> FollowRequestedAsync(string signature, string method, string path, string queryString, Dictionary<string, string> requestHeaders, ActivityFollow activity, string body)
        {
            // Validate
            var sigValidation = await ValidateSignature(activity.actor, signature, method, path, queryString, requestHeaders, body);
            if (!sigValidation.SignatureIsValidated) return false;

            // Prepare data
            var followerUserName = SigValidationResultExtractor.GetUserName(sigValidation);
            var followerHost = SigValidationResultExtractor.GetHost(sigValidation);
            var followerInbox = sigValidation.User.inbox;
            var followerSharedInbox = SigValidationResultExtractor.GetSharedInbox(sigValidation);
            var twitterUser = activity.apObject.Split('/').Last().Replace("@", string.Empty).ToLowerInvariant().Trim();

            // Make sure to only keep routes
            followerInbox = OnlyKeepRoute(followerInbox, followerHost);
            followerSharedInbox = OnlyKeepRoute(followerSharedInbox, followerHost);
            
            // Validate Moderation status
            var followerModPolicy = _moderationRepository.GetModerationType(ModerationEntityTypeEnum.Follower);
            if (followerModPolicy != ModerationTypeEnum.None)
            {
                var followerStatus = _moderationRepository.CheckStatus(ModerationEntityTypeEnum.Follower, $"@{followerUserName}@{followerHost}");
                
                if(followerModPolicy == ModerationTypeEnum.WhiteListing && followerStatus != ModeratedTypeEnum.WhiteListed || 
                   followerModPolicy == ModerationTypeEnum.BlackListing && followerStatus == ModeratedTypeEnum.BlackListed)
                    return await SendRejectFollowAsync(activity, followerHost);
            }

            // Validate TwitterAccount status
            var twitterAccountModPolicy = _moderationRepository.GetModerationType(ModerationEntityTypeEnum.TwitterAccount);
            if (twitterAccountModPolicy != ModerationTypeEnum.None)
            {
                var twitterUserStatus = _moderationRepository.CheckStatus(ModerationEntityTypeEnum.TwitterAccount, twitterUser);
                if (twitterAccountModPolicy == ModerationTypeEnum.WhiteListing && twitterUserStatus != ModeratedTypeEnum.WhiteListed ||
                    twitterAccountModPolicy == ModerationTypeEnum.BlackListing && twitterUserStatus == ModeratedTypeEnum.BlackListed)
                    return await SendRejectFollowAsync(activity, followerHost);
            }

            // Validate follower count < MaxFollowsPerUser
            if (_instanceSettings.MaxFollowsPerUser > 0) {
                var follower = await _followerDal.GetFollowerAsync(followerUserName, followerHost);

                if (follower != null && follower.Followings.Count + 1 > _instanceSettings.MaxFollowsPerUser)
                {
                    return await SendRejectFollowAsync(activity, followerHost);
                }
            }

            // Validate User Protected
            var user = _twitterUserService.GetUser(twitterUser);
            if (!user.Protected)
            {
                // Execute
                await _processFollowUser.ExecuteAsync(followerUserName, followerHost, twitterUser, followerInbox, followerSharedInbox, activity.actor);

                return await SendAcceptFollowAsync(activity, followerHost);
            }
            else
            {
                return await SendRejectFollowAsync(activity, followerHost);
            }
        }
        
        private async Task<bool> SendAcceptFollowAsync(ActivityFollow activity, string followerHost)
        {
            var acceptFollow = new ActivityAcceptFollow()
            {
                context = "https://www.w3.org/ns/activitystreams",
                id = $"{activity.apObject}#accepts/follows/{Guid.NewGuid()}",
                type = "Accept",
                actor = activity.apObject,
                apObject = new ActivityFollow()
                {
                    id = activity.id,
                    type = activity.type,
                    actor = activity.actor,
                    apObject = activity.apObject
                }
            };
            var result = await _activityPubService.PostDataAsync(acceptFollow, followerHost, activity.apObject);
            return result == HttpStatusCode.Accepted ||
                   result == HttpStatusCode.OK; //TODO: revamp this for better error handling
        }

        public async Task<bool> SendRejectFollowAsync(ActivityFollow activity, string followerHost)
        {
            var acceptFollow = new ActivityRejectFollow()
            {
                context = "https://www.w3.org/ns/activitystreams",
                id = $"{activity.apObject}#rejects/follows/{Guid.NewGuid()}",
                type = "Reject",
                actor = activity.apObject,
                apObject = new ActivityFollow()
                {
                    id = activity.id,
                    type = activity.type,
                    actor = activity.actor,
                    apObject = activity.apObject
                }
            };
            var result = await _activityPubService.PostDataAsync(acceptFollow, followerHost, activity.apObject);
            return result == HttpStatusCode.Accepted ||
                   result == HttpStatusCode.OK; //TODO: revamp this for better error handling
        }
        
        private string OnlyKeepRoute(string inbox, string host)
        {
            if (string.IsNullOrWhiteSpace(inbox)) 
                return null;

            if (inbox.Contains(host))
                inbox = inbox.Split(new[] { host }, StringSplitOptions.RemoveEmptyEntries).Last();

            return inbox;
        }

        public async Task<bool> UndoFollowRequestedAsync(string signature, string method, string path, string queryString,
            Dictionary<string, string> requestHeaders, ActivityUndoFollow activity, string body)
        {
            // Validate
            var sigValidation = await ValidateSignature(activity.actor, signature, method, path, queryString, requestHeaders, body);
            if (!sigValidation.SignatureIsValidated) return false;

            // Save Follow in DB
            var followerUserName = sigValidation.User.preferredUsername.ToLowerInvariant();
            var followerHost = sigValidation.User.url.Replace("https://", string.Empty).Split('/').First();
            //var followerInbox = sigValidation.User.inbox;
            var twitterUser = activity.apObject.apObject.Split('/').Last().Replace("@", string.Empty);
            await _processUndoFollowUser.ExecuteAsync(followerUserName, followerHost, twitterUser);

            // Send Accept Activity
            var acceptFollow = new ActivityAcceptUndoFollow()
            {
                context = "https://www.w3.org/ns/activitystreams",
                id = $"{activity.apObject.apObject}#accepts/undofollows/{Guid.NewGuid()}",
                type = "Accept",
                actor = activity.apObject.apObject,
                apObject = new ActivityUndoFollow()
                {
                    id = activity.id,
                    type = activity.type,
                    actor = activity.actor,
                    apObject = activity.apObject
                }
            };
            var result = await _activityPubService.PostDataAsync(acceptFollow, followerHost, activity.apObject.apObject);
            return result == HttpStatusCode.Accepted || result == HttpStatusCode.OK; //TODO: revamp this for better error handling
        }

        public async Task<bool> DeleteRequestedAsync(string signature, string method, string path, string queryString, Dictionary<string, string> requestHeaders,
            ActivityDelete activity, string body)
        {
            // Validate
            var sigValidation = await ValidateSignature(activity.actor, signature, method, path, queryString, requestHeaders, body);
            if (!sigValidation.SignatureIsValidated) return false;

            // Remove user and followings
            var followerUserName = SigValidationResultExtractor.GetUserName(sigValidation);
            var followerHost = SigValidationResultExtractor.GetHost(sigValidation);

            await _processDeleteUser.ExecuteAsync(followerUserName, followerHost);

            return true;
        }

        private async Task<SignatureValidationResult> ValidateSignature(string actor, string rawSig, string method, string path, string queryString, Dictionary<string, string> requestHeaders, string body)
        {
            //Check Date Validity
            var date = requestHeaders["date"];
            var d = DateTime.Parse(date).ToUniversalTime();
            var now = DateTime.UtcNow;
            var delta = Math.Abs((d - now).TotalSeconds);
            if (delta > 30) return new SignatureValidationResult { SignatureIsValidated = false };
            
            //Check Digest
            var digest = requestHeaders["digest"];
            var digestHash = digest.Split(new [] {"SHA-256="},StringSplitOptions.RemoveEmptyEntries).LastOrDefault();
            var calculatedDigestHash = _cryptoService.ComputeSha256Hash(body);
            if (digestHash != calculatedDigestHash) return new SignatureValidationResult { SignatureIsValidated = false };

            //Check Signature
            var signatures = rawSig.Split(',');
            var signature_header = new Dictionary<string, string>();
            foreach (var signature in signatures)
            {
                var m = HeaderRegexes.HeaderSignature.Match(signature);
                signature_header.Add(m.Groups[1].ToString(), m.Groups[2].ToString());
            }

            var key_id = signature_header["keyId"];
            var headers = signature_header["headers"];
            var algorithm = signature_header["algorithm"];
            var sig = Convert.FromBase64String(signature_header["signature"]);

            // Retrieve User
            var remoteUser = await _activityPubService.GetUser(actor);

            // Prepare Key data
            var toDecode = remoteUser.publicKey.publicKeyPem.Trim().Remove(0, remoteUser.publicKey.publicKeyPem.IndexOf('\n'));
            toDecode = toDecode.Remove(toDecode.LastIndexOf('\n')).Replace("\n", "");
            var signKey = ASN1.ToRSA(Convert.FromBase64String(toDecode));

            var toSign = new StringBuilder();
            foreach (var headerKey in headers.Split(' '))
            {
                if (headerKey == "(request-target)") toSign.Append($"(request-target): {method.ToLower()} {path}{queryString}\n");
                else toSign.Append($"{headerKey}: {string.Join(", ", requestHeaders[headerKey])}\n");
            }
            toSign.Remove(toSign.Length - 1, 1);

            // Import key
            var key = new RSACryptoServiceProvider();
            var rsaKeyInfo = key.ExportParameters(false);
            rsaKeyInfo.Modulus = Convert.FromBase64String(toDecode);
            key.ImportParameters(rsaKeyInfo);

            // Trust and Verify
            var result = signKey.VerifyData(Encoding.UTF8.GetBytes(toSign.ToString()), sig, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

            return new SignatureValidationResult()
            {
                SignatureIsValidated = result,
                User = remoteUser
            };
        }
    }

    public class SignatureValidationResult 
    {
        public bool SignatureIsValidated { get; set; }
        public Actor User { get; set; }
    }
}