path: root/Timeline/Services/TimelineService.cs

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using SixLabors.ImageSharp;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Threading.Tasks;
using TimelineApp.Entities;
using TimelineApp.Models;
using TimelineApp.Models.Validation;
using static TimelineApp.Resources.Services.TimelineService;

namespace TimelineApp.Services
{
    public enum TimelineUserRelationshipType
    {
        Own = 0b1,
        Join = 0b10,
        Default = Own | Join
    }

    public class TimelineUserRelationship
    {
        public TimelineUserRelationship(TimelineUserRelationshipType type, long userId)
        {
            Type = type;
            UserId = userId;
        }

        public TimelineUserRelationshipType Type { get; set; }
        public long UserId { get; set; }
    }

    public class DataWithType
    {
#pragma warning disable CA1819 // Properties should not return arrays
        public byte[] Data { get; set; } = default!;
#pragma warning restore CA1819 // Properties should not return arrays
        public string Type { get; set; } = default!;
    }

    /// <summary>
    /// This define the common interface of both personal timeline and normal timeline.
    /// </summary>
    /// <remarks>
    /// The "name" parameter in each method has different meaning.
    /// <see cref="IOrdinaryTimelineService"/> => name of the ordinary timeline
    /// <see cref="IPersonalTimelineService"/> => username of the owner of the personal timeline
    /// <see cref="ITimelineService"/> => username if begin with '@' otherwise timeline name
    ///
    /// <see cref="ArgumentException"/> is thrown when name is illegal.
    /// For ordinary timeline, it means the name is not a valid timeline name.
    /// For personal timeline, it means the name is not a valid username.
    /// 
    /// <see cref="TimelineNotExistException"> is thrown when timeline does not exist.
    /// For ordinary timeline, it means the timeline of the name does not exist.
    /// For personal timeline, it means the user with the username does not exist and the inner exception should be a <see cref="UserNotExistException"/>.
    /// </remarks>
    public interface IBaseTimelineService
    {
        /// <summary>
        /// Get the timeline info.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <returns>The timeline info.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        Task<Timeline> GetTimeline(string name);

        /// <summary>
        /// Set the properties of a timeline. 
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="newProperties">The new properties. Null member means not to change.</param>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> or <paramref name="newProperties"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        Task ChangeProperty(string name, TimelineChangePropertyRequest newProperties);

        /// <summary>
        /// Get all the posts in the timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <returns>A list of all posts.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        Task<List<TimelinePost>> GetPosts(string name);

        /// <summary>
        /// Get the data of a post.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="postId">The id of the post.</param>
        /// <returns>The data and its type.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when post of <paramref name="postId"/> does not exist or has been deleted.</exception>
        /// <exception cref="InvalidOperationException">Thrown when post has no data. See remarks.</exception>
        /// <remarks>
        /// Use this method to retrieve the image of image post.
        /// </remarks>
        Task<DataWithType> GetPostData(string name, long postId);

        /// <summary>
        /// Create a new text post in timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="authorId">The author's user id.</param>
        /// <param name="text">The content text.</param>
        /// <param name="time">The time of the post. If null, then use current time.</param>
        /// <returns>The info of the created post.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> or <paramref name="text"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="UserNotExistException">Thrown if user with <paramref name="authorId"/> does not exist.</exception>
        Task<TimelinePost> CreateTextPost(string name, long authorId, string text, DateTime? time);

        /// <summary>
        /// Create a new image post in timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="authorId">The author's user id.</param>
        /// <param name="data">The image data.</param>
        /// <param name="time">The time of the post. If null, then use current time.</param>
        /// <returns>The info of the created post.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> or <paramref name="data"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="UserNotExistException">Thrown if user with <paramref name="authorId"/> does not exist.</exception>
        /// <exception cref="ImageException">Thrown if data is not a image. Validated by <see cref="ImageValidator"/>.</exception>
        Task<TimelinePost> CreateImagePost(string name, long authorId, byte[] data, DateTime? time);

        /// <summary>
        /// Delete a post.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="id">The id of the post to delete.</param>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelinePostNotExistException">
        /// Thrown when the post with given id does not exist or is deleted already.
        /// </exception>
        /// <remarks>
        /// First use <see cref="IBaseTimelineService.HasPostModifyPermission(string, long, string)"/>
        /// to check the permission.
        /// </remarks>
        Task DeletePost(string name, long id);

        /// <summary>
        /// Remove members to a timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="add">A list of usernames of members to add. May be null.</param>
        /// <param name="remove">A list of usernames of members to remove. May be null.</param>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="ArgumentException">Thrown when names in <paramref name="add"/> or <paramref name="remove"/> is not a valid username.</exception>
        /// <exception cref="UserNotExistException">
        /// Thrown when one of the user to change does not exist.
        /// </exception>
        /// <remarks>
        /// Operating on a username that is of bad format or does not exist always throws.
        /// Add a user that already is a member has no effects.
        /// Remove a user that is not a member also has not effects.
        /// Add and remove an identical user results in no effects.
        /// More than one same usernames are regarded as one.
        /// </remarks>
        Task ChangeMember(string name, IList<string>? add, IList<string>? remove);

        /// <summary>
        /// Check whether a user can manage(change timeline info, member, ...) a timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="userId">The user id.</param>
        /// <returns>True if the user can manage the timeline, otherwise false.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <remarks>
        /// This method does not check whether visitor is administrator.
        /// Return false if user with user id does not exist.
        /// </remarks>
        Task<bool> HasManagePermission(string name, long userId);

        /// <summary>
        /// Verify whether a visitor has the permission to read a timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="visitorId">The id of the user to check on. Null means visitor without account.</param>
        /// <returns>True if can read, false if can't read.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <remarks>
        /// This method does not check whether visitor is administrator.
        /// Return false if user with visitor id does not exist.
        /// </remarks>
        Task<bool> HasReadPermission(string name, long? visitorId);

        /// <summary>
        /// Verify whether a user has the permission to modify a post.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="modifierId">The id of the user to check on.</param>
        /// <returns>True if can modify, false if can't modify.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelinePostNotExistException">
        /// Thrown when the post with given id does not exist or is deleted already.
        /// </exception>
        /// <remarks>
        /// This method does not check whether the user is administrator.
        /// It only checks whether he is the author of the post or the owner of the timeline.
        /// Return false when user with modifier id does not exist.
        /// </remarks>
        Task<bool> HasPostModifyPermission(string name, long id, long modifierId);

        /// <summary>
        /// Verify whether a user is member of a timeline.
        /// </summary>
        /// <param name="name">See remarks of <see cref="IBaseTimelineService"/>.</param>
        /// <param name="userId">The id of user to check on.</param>
        /// <returns>True if it is a member, false if not.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <exception cref="TimelineNotExistException">See remarks of <see cref="IBaseTimelineService"/>.</exception>
        /// <remarks>
        /// Timeline owner is also considered as a member.
        /// Return false when user with user id does not exist.
        /// </remarks>
        Task<bool> IsMemberOf(string name, long userId);
    }

    /// <summary>
    /// Service for normal timeline.
    /// </summary>
    public interface ITimelineService : IBaseTimelineService
    {
        /// <summary>
        /// Get all timelines including personal timelines.
        /// </summary>
        /// <param name="relate">Filter timelines related (own or is a member) to specific user.</param>
        /// <param name="visibility">Filter timelines with given visibility. If null or empty, all visibilities are returned. Duplicate value are ignored.</param>
        /// <returns>The list of timelines.</returns>
        /// <remarks>
        /// If user with related user id does not exist, empty list will be returned.
        /// </remarks>
        Task<List<Timeline>> GetTimelines(TimelineUserRelationship? relate = null, List<TimelineVisibility>? visibility = null);

        /// <summary>
        /// Create a timeline.
        /// </summary>
        /// <param name="name">The name of the timeline.</param>
        /// <param name="owner">The id of owner of the timeline.</param>
        /// <returns>The info of the new timeline.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">Thrown when timeline name is invalid.</exception>
        /// <exception cref="ConflictException">Thrown when the timeline already exists.</exception>
        /// <exception cref="UserNotExistException">Thrown when the owner user does not exist.</exception>
        Task<Timeline> CreateTimeline(string name, long owner);

        /// <summary>
        /// Delete a timeline.
        /// </summary>
        /// <param name="name">The name of the timeline.</param>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">Thrown when timeline name is invalid.</exception>
        /// <exception cref="TimelineNotExistException">Thrown when the timeline does not exist.</exception>
        Task DeleteTimeline(string name);
    }

    public interface IOrdinaryTimelineService : IBaseTimelineService
    {

    }

    public interface IPersonalTimelineService : IBaseTimelineService
    {

    }

    public abstract class BaseTimelineManager : IBaseTimelineService
    {
        protected BaseTimelineManager(ILoggerFactory loggerFactory, DatabaseContext database, IImageValidator imageValidator, IDataManager dataManager, IUserService userService, IClock clock)
        {
            _logger = loggerFactory.CreateLogger<BaseTimelineManager>();
            Clock = clock;
            Database = database;
            ImageValidator = imageValidator;
            DataManager = dataManager;
            UserService = userService;
        }

        private ILogger<BaseTimelineManager> _logger;

        protected IClock Clock { get; }

        protected UsernameValidator UsernameValidator { get; } = new UsernameValidator();

        protected DatabaseContext Database { get; }

        protected IImageValidator ImageValidator { get; }
        protected IDataManager DataManager { get; }
        protected IUserService UserService { get; }

        /// <summary>
        /// Find the timeline id by the name.
        /// For details, see remarks.
        /// </summary>
        /// <param name="name">The username or the timeline name. See remarks.</param>
        /// <returns>The id of the timeline entity.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="name"/> is null.</exception>
        /// <exception cref="ArgumentException">Thrown when <paramref name="name"/> is illegal. It is not a valid timeline name (for normal timeline service) or a valid username (for personal timeline service).</exception>
        /// <exception cref="TimelineNotExistException">
        /// Thrown when timeline does not exist.
        /// For normal timeline, it means the name does not exist.
        /// For personal timeline, it means the user of that username does not exist
        /// and the inner exception should be a <see cref="UserNotExistException"/>.
        /// </exception>
        /// <remarks>
        /// This is the common but different part for both types of timeline service.
        /// For class that implements <see cref="IPersonalTimelineService"/>, this method should
        /// find the timeline entity id by the given <paramref name="name"/> as the username of the owner.
        /// For class that implements <see cref="ITimelineService"/>, this method should
        /// find the timeline entity id by the given <paramref name="name"/> as the timeline name.
        /// This method should be called by many other method that follows the contract.
        /// </remarks>
        protected abstract Task<long> FindTimelineId(string name);

        public async Task<Timeline> GetTimeline(string name)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);

            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).SingleAsync();

            var timelineMemberEntities = await Database.TimelineMembers.Where(m => m.TimelineId == timelineId).Select(m => new { m.UserId }).ToListAsync();

            var owner = await UserService.GetUserById(timelineEntity.OwnerId);

            var members = new List<User>();
            foreach (var memberEntity in timelineMemberEntities)
            {
                members.Add(await UserService.GetUserById(memberEntity.UserId));
            }

            return new Timeline
            {
                Name = timelineEntity.Name ?? ("@" + owner.Username),
                Description = timelineEntity.Description ?? "",
                Owner = owner,
                Visibility = timelineEntity.Visibility,
                Members = members
            };
        }

        public async Task<List<TimelinePost>> GetPosts(string name)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);
            var postEntities = await Database.TimelinePosts.OrderBy(p => p.Time).Where(p => p.TimelineId == timelineId && p.Content != null).ToListAsync();

            var posts = new List<TimelinePost>();
            foreach (var entity in postEntities)
            {
                if (entity.Content != null) // otherwise it is deleted
                {
                    var author = await UserService.GetUserById(entity.AuthorId);

                    var type = entity.ContentType;

                    ITimelinePostContent content = type switch
                    {
                        TimelinePostContentTypes.Text => new TextTimelinePostContent(entity.Content),
                        TimelinePostContentTypes.Image => new ImageTimelinePostContent(entity.Content),
                        _ => throw new DatabaseCorruptedException(string.Format(CultureInfo.InvariantCulture, ExceptionDatabaseUnknownContentType, type))
                    };

                    posts.Add(new TimelinePost
                    {
                        Id = entity.LocalId,
                        Content = content,
                        Author = author,
                        Time = entity.Time,
                        LastUpdated = entity.LastUpdated
                    });
                }
            }
            return posts;
        }
        public async Task<DataWithType> GetPostData(string name, long postId)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);
            var postEntity = await Database.TimelinePosts.Where(p => p.LocalId == postId).SingleOrDefaultAsync();

            if (postEntity == null)
                throw new TimelinePostNotExistException(name, postId);

            if (postEntity.Content == null)
                throw new TimelinePostNotExistException(name, postId, true);

            if (postEntity.ContentType != TimelinePostContentTypes.Image)
                throw new InvalidOperationException(ExceptionGetDataNonImagePost);

            var tag = postEntity.Content;

            byte[] data;

            try
            {
                data = await DataManager.GetEntry(tag);
            }
            catch (InvalidOperationException e)
            {
                throw new DatabaseCorruptedException(ExceptionGetDataDataEntryNotExist, e);
            }

            if (postEntity.ExtraContent == null)
            {
                _logger.LogWarning(LogGetDataNoFormat);
                var format = Image.DetectFormat(data);
                postEntity.ExtraContent = format.DefaultMimeType;
                await Database.SaveChangesAsync();
            }

            return new DataWithType
            {
                Data = data,
                Type = postEntity.ExtraContent
            };
        }

        public async Task<TimelinePost> CreateTextPost(string name, long authorId, string text, DateTime? time)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));
            if (text == null)
                throw new ArgumentNullException(nameof(text));

            var timelineId = await FindTimelineId(name);
            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).SingleAsync();

            var author = await UserService.GetUserById(authorId);

            var currentTime = Clock.GetCurrentTime();
            var finalTime = time ?? currentTime;

            timelineEntity.CurrentPostLocalId += 1;

            var postEntity = new TimelinePostEntity
            {
                LocalId = timelineEntity.CurrentPostLocalId,
                ContentType = TimelinePostContentTypes.Text,
                Content = text,
                AuthorId = authorId,
                TimelineId = timelineId,
                Time = finalTime,
                LastUpdated = currentTime
            };
            Database.TimelinePosts.Add(postEntity);
            await Database.SaveChangesAsync();

            return new TimelinePost
            {
                Id = postEntity.LocalId,
                Content = new TextTimelinePostContent(text),
                Author = author,
                Time = finalTime,
                LastUpdated = currentTime
            };
        }

        public async Task<TimelinePost> CreateImagePost(string name, long authorId, byte[] data, DateTime? time)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));
            if (data == null)
                throw new ArgumentNullException(nameof(data));

            var timelineId = await FindTimelineId(name);
            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).SingleAsync();

            var author = await UserService.GetUserById(authorId);

            var imageFormat = await ImageValidator.Validate(data);

            var imageFormatText = imageFormat.DefaultMimeType;

            var tag = await DataManager.RetainEntry(data);

            var currentTime = Clock.GetCurrentTime();
            var finalTime = time ?? currentTime;

            timelineEntity.CurrentPostLocalId += 1;

            var postEntity = new TimelinePostEntity
            {
                LocalId = timelineEntity.CurrentPostLocalId,
                ContentType = TimelinePostContentTypes.Image,
                Content = tag,
                ExtraContent = imageFormatText,
                AuthorId = authorId,
                TimelineId = timelineId,
                Time = finalTime,
                LastUpdated = currentTime
            };
            Database.TimelinePosts.Add(postEntity);
            await Database.SaveChangesAsync();

            return new TimelinePost
            {
                Id = postEntity.LocalId,
                Content = new ImageTimelinePostContent(tag),
                Author = author,
                Time = finalTime,
                LastUpdated = currentTime
            };
        }

        public async Task DeletePost(string name, long id)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);

            var post = await Database.TimelinePosts.Where(p => p.TimelineId == timelineId && p.LocalId == id).SingleOrDefaultAsync();

            if (post == null)
                throw new TimelinePostNotExistException(name, id);

            string? dataTag = null;

            if (post.ContentType == TimelinePostContentTypes.Image)
            {
                dataTag = post.Content;
            }

            post.Content = null;
            post.LastUpdated = Clock.GetCurrentTime();

            await Database.SaveChangesAsync();

            if (dataTag != null)
            {
                await DataManager.FreeEntry(dataTag);
            }
        }

        public async Task ChangeProperty(string name, TimelineChangePropertyRequest newProperties)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));
            if (newProperties == null)
                throw new ArgumentNullException(nameof(newProperties));

            var timelineId = await FindTimelineId(name);

            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).SingleAsync();

            if (newProperties.Description != null)
            {
                timelineEntity.Description = newProperties.Description;
            }

            if (newProperties.Visibility.HasValue)
            {
                timelineEntity.Visibility = newProperties.Visibility.Value;
            }

            await Database.SaveChangesAsync();
        }

        public async Task ChangeMember(string name, IList<string>? add, IList<string>? remove)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            List<string>? RemoveDuplicateAndCheckFormat(IList<string>? list, string paramName)
            {
                if (list != null)
                {
                    List<string> result = new List<string>();
                    var count = list.Count;
                    for (var index = 0; index < count; index++)
                    {
                        var username = list[index];
                        if (result.Contains(username))
                        {
                            continue;
                        }
                        var (validationResult, message) = UsernameValidator.Validate(username);
                        if (!validationResult)
                            throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, ExceptionChangeMemberUsernameBadFormat, index), nameof(paramName));
                        result.Add(username);
                    }
                    return result;
                }
                else
                {
                    return null;
                }
            }
            var simplifiedAdd = RemoveDuplicateAndCheckFormat(add, nameof(add));
            var simplifiedRemove = RemoveDuplicateAndCheckFormat(remove, nameof(remove));

            // remove those both in add and remove
            if (simplifiedAdd != null && simplifiedRemove != null)
            {
                var usersToClean = simplifiedRemove.Where(u => simplifiedAdd.Contains(u)).ToList();
                foreach (var u in usersToClean)
                {
                    simplifiedAdd.Remove(u);
                    simplifiedRemove.Remove(u);
                }
            }

            var timelineId = await FindTimelineId(name);

            async Task<List<long>?> CheckExistenceAndGetId(List<string>? list)
            {
                if (list == null)
                    return null;

                List<long> result = new List<long>();
                foreach (var username in list)
                {
                    result.Add(await UserService.GetUserIdByUsername(username));
                }
                return result;
            }
            var userIdsAdd = await CheckExistenceAndGetId(simplifiedAdd);
            var userIdsRemove = await CheckExistenceAndGetId(simplifiedRemove);

            if (userIdsAdd != null)
            {
                var membersToAdd = userIdsAdd.Select(id => new TimelineMemberEntity { UserId = id, TimelineId = timelineId }).ToList();
                Database.TimelineMembers.AddRange(membersToAdd);
            }

            if (userIdsRemove != null)
            {
                var membersToRemove = await Database.TimelineMembers.Where(m => m.TimelineId == timelineId && userIdsRemove.Contains(m.UserId)).ToListAsync();
                Database.TimelineMembers.RemoveRange(membersToRemove);
            }

            await Database.SaveChangesAsync();
        }

        public async Task<bool> HasManagePermission(string name, long userId)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);
            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).Select(t => new { t.OwnerId }).SingleAsync();

            return userId == timelineEntity.OwnerId;
        }

        public async Task<bool> HasReadPermission(string name, long? visitorId)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);

            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).Select(t => new { t.Visibility }).SingleAsync();

            if (timelineEntity.Visibility == TimelineVisibility.Public)
                return true;

            if (timelineEntity.Visibility == TimelineVisibility.Register && visitorId != null)
                return true;

            if (visitorId == null)
            {
                return false;
            }
            else
            {
                var memberEntity = await Database.TimelineMembers.Where(m => m.UserId == visitorId && m.TimelineId == timelineId).SingleOrDefaultAsync();
                return memberEntity != null;
            }
        }

        public async Task<bool> HasPostModifyPermission(string name, long id, long modifierId)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);

            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).Select(t => new { t.OwnerId }).SingleAsync();

            var postEntity = await Database.TimelinePosts.Where(p => p.Id == id).Select(p => new { p.AuthorId }).SingleOrDefaultAsync();

            if (postEntity == null)
                throw new TimelinePostNotExistException(name, id);

            return timelineEntity.OwnerId == modifierId || postEntity.AuthorId == modifierId;
        }

        public async Task<bool> IsMemberOf(string name, long userId)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            var timelineId = await FindTimelineId(name);

            var timelineEntity = await Database.Timelines.Where(t => t.Id == timelineId).Select(t => new { t.OwnerId }).SingleAsync();

            if (userId == timelineEntity.OwnerId)
                return true;

            return await Database.TimelineMembers.AnyAsync(m => m.TimelineId == timelineId && m.UserId == userId);
        }
    }

    public class OrdinaryTimelineService : BaseTimelineManager, IOrdinaryTimelineService
    {
        private readonly TimelineNameValidator _timelineNameValidator = new TimelineNameValidator();

        private void ValidateTimelineName(string name, string paramName)
        {
            if (!_timelineNameValidator.Validate(name, out var message))
            {
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, ExceptionTimelineNameBadFormat, message), paramName);
            }
        }

        public OrdinaryTimelineService(ILoggerFactory loggerFactory, DatabaseContext database, IImageValidator imageValidator, IDataManager dataManager, IUserService userService, IClock clock)
            : base(loggerFactory, database, imageValidator, dataManager, userService, clock)
        {

        }

        protected override async Task<long> FindTimelineId(string name)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            ValidateTimelineName(name, nameof(name));

            var timelineEntity = await Database.Timelines.Where(t => t.Name == name).Select(t => new { t.Id }).SingleOrDefaultAsync();

            if (timelineEntity == null)
            {
                throw new TimelineNotExistException(name);
            }
            else
            {
                return timelineEntity.Id;
            }
        }
    }

    public class PersonalTimelineService : BaseTimelineManager, IPersonalTimelineService
    {
        public PersonalTimelineService(ILoggerFactory loggerFactory, DatabaseContext database, IImageValidator imageValidator, IDataManager dataManager, IUserService userService, IClock clock)
            : base(loggerFactory, database, imageValidator, dataManager, userService, clock)
        {

        }

        protected override async Task<long> FindTimelineId(string name)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            long userId;
            try
            {
                userId = await UserService.GetUserIdByUsername(name);
            }
            catch (ArgumentException e)
            {
                throw new ArgumentException(ExceptionFindTimelineUsernameBadFormat, nameof(name), e);
            }
            catch (UserNotExistException e)
            {
                throw new TimelineNotExistException(name, e);
            }

            var timelineEntity = await Database.Timelines.Where(t => t.OwnerId == userId && t.Name == null).Select(t => new { t.Id }).SingleOrDefaultAsync();

            if (timelineEntity != null)
            {
                return timelineEntity.Id;
            }
            else
            {
                var newTimelineEntity = new TimelineEntity
                {
                    CurrentPostLocalId = 0,
                    Name = null,
                    OwnerId = userId,
                    Visibility = TimelineVisibility.Register,
                    CreateTime = Clock.GetCurrentTime()
                };
                Database.Timelines.Add(newTimelineEntity);
                await Database.SaveChangesAsync();

                return newTimelineEntity.Id;
            }
        }
    }

    public class TimelineService : ITimelineService
    {
        private readonly TimelineNameValidator _timelineNameValidator = new TimelineNameValidator();

        private readonly DatabaseContext _database;

        private readonly IUserService _userService;
        private readonly IClock _clock;

        private readonly IOrdinaryTimelineService _ordinaryTimelineService;
        private readonly IPersonalTimelineService _personalTimelineService;

        public TimelineService(DatabaseContext database, IUserService userService, IClock clock, IOrdinaryTimelineService ordinaryTimelineService, IPersonalTimelineService personalTimelineService)
        {
            _database = database;
            _userService = userService;
            _clock = clock;
            _ordinaryTimelineService = ordinaryTimelineService;
            _personalTimelineService = personalTimelineService;
        }

        private void ValidateTimelineName(string name, string paramName)
        {
            if (!_timelineNameValidator.Validate(name, out var message))
            {
                throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, ExceptionTimelineNameBadFormat, message), paramName);
            }
        }

        public async Task<List<Timeline>> GetTimelines(TimelineUserRelationship? relate = null, List<TimelineVisibility>? visibility = null)
        {
            List<TimelineEntity> entities;

            IQueryable<TimelineEntity> ApplyTimelineVisibilityFilter(IQueryable<TimelineEntity> query)
            {
                if (visibility != null && visibility.Count != 0)
                {
                    return query.Where(t => visibility.Contains(t.Visibility));
                }
                return query;
            }

            bool allVisibilities = visibility == null || visibility.Count == 0;

            if (relate == null)
            {
                entities = await ApplyTimelineVisibilityFilter(_database.Timelines).Include(t => t.Members).ToListAsync();
            }
            else
            {
                entities = new List<TimelineEntity>();

                if ((relate.Type & TimelineUserRelationshipType.Own) != 0)
                {
                    entities.AddRange(await ApplyTimelineVisibilityFilter(_database.Timelines.Where(t => t.OwnerId == relate.UserId)).Include(t => t.Members).ToListAsync());
                }

                if ((relate.Type & TimelineUserRelationshipType.Join) != 0)
                {
                    entities.AddRange(await ApplyTimelineVisibilityFilter(_database.TimelineMembers.Where(m => m.UserId == relate.UserId).Include(m => m.Timeline).ThenInclude(t => t.Members).Select(m => m.Timeline)).ToListAsync());
                }
            }

            var result = new List<Timeline>();

            foreach (var entity in entities)
            {
                var owner = await _userService.GetUserById(entity.OwnerId);
                var timeline = new Timeline
                {
                    Name = entity.Name ?? ("@" + owner.Username),
                    Description = entity.Description ?? "",
                    Owner = owner,
                    Visibility = entity.Visibility,
                    Members = new List<User>()
                };

                foreach (var m in entity.Members)
                {
                    timeline.Members.Add(await _userService.GetUserById(m.UserId));
                }

                result.Add(timeline);
            }

            return result;
        }

        public async Task<Timeline> CreateTimeline(string name, long owner)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            ValidateTimelineName(name, nameof(name));

            var user = await _userService.GetUserById(owner);

            var conflict = await _database.Timelines.AnyAsync(t => t.Name == name);

            if (conflict)
                throw new ConflictException(ExceptionTimelineNameConflict);

            var newEntity = new TimelineEntity
            {
                CurrentPostLocalId = 0,
                Name = name,
                OwnerId = owner,
                Visibility = TimelineVisibility.Register,
                CreateTime = _clock.GetCurrentTime()
            };

            _database.Timelines.Add(newEntity);
            await _database.SaveChangesAsync();

            return new Timeline
            {
                Name = name,
                Description = "",
                Owner = user,
                Visibility = newEntity.Visibility,
                Members = new List<User>()
            };
        }

        public async Task DeleteTimeline(string name)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            ValidateTimelineName(name, nameof(name));

            var entity = await _database.Timelines.Where(t => t.Name == name).SingleOrDefaultAsync();

            if (entity == null)
                throw new TimelineNotExistException(name);

            _database.Timelines.Remove(entity);
            await _database.SaveChangesAsync();
        }


        private IBaseTimelineService BranchName(string name, out string realName)
        {
            if (name == null)
                throw new ArgumentNullException(nameof(name));

            if (name.StartsWith('@'))
            {
                realName = name.Substring(1);
                return _personalTimelineService;
            }
            else
            {
                realName = name;
                return _ordinaryTimelineService;
            }
        }

        public Task<Timeline> GetTimeline(string name)
        {
            var s = BranchName(name, out var realName);
            return s.GetTimeline(realName);
        }

        public Task ChangeProperty(string name, TimelineChangePropertyRequest newProperties)
        {
            var s = BranchName(name, out var realName);
            return s.ChangeProperty(realName, newProperties);
        }

        public Task<List<TimelinePost>> GetPosts(string name)
        {
            var s = BranchName(name, out var realName);
            return s.GetPosts(realName);
        }

        public Task<DataWithType> GetPostData(string name, long postId)
        {
            var s = BranchName(name, out var realName);
            return s.GetPostData(realName, postId);
        }

        public Task<TimelinePost> CreateTextPost(string name, long authorId, string text, DateTime? time)
        {
            var s = BranchName(name, out var realName);
            return s.CreateTextPost(realName, authorId, text, time);
        }

        public Task<TimelinePost> CreateImagePost(string name, long authorId, byte[] data, DateTime? time)
        {
            var s = BranchName(name, out var realName);
            return s.CreateImagePost(realName, authorId, data, time);
        }

        public Task DeletePost(string name, long id)
        {
            var s = BranchName(name, out var realName);
            return s.DeletePost(realName, id);
        }

        public Task ChangeMember(string name, IList<string>? add, IList<string>? remove)
        {
            var s = BranchName(name, out var realName);
            return s.ChangeMember(realName, add, remove);
        }

        public Task<bool> HasManagePermission(string name, long userId)
        {
            var s = BranchName(name, out var realName);
            return s.HasManagePermission(realName, userId);
        }

        public Task<bool> HasReadPermission(string name, long? visitorId)
        {
            var s = BranchName(name, out var realName);
            return s.HasReadPermission(realName, visitorId);
        }

        public Task<bool> HasPostModifyPermission(string name, long id, long modifierId)
        {
            var s = BranchName(name, out var realName);
            return s.HasPostModifyPermission(realName, id, modifierId);
        }

        public Task<bool> IsMemberOf(string name, long userId)
        {
            var s = BranchName(name, out var realName);
            return s.IsMemberOf(realName, userId);
        }
    }
}