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

namespace Timeline.Services
{
    public class PostData : ICacheableData
    {
#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!;
        public string ETag { get; set; } = default!;
        public DateTime? LastModified { get; set; } // TODO: Why nullable?
    }

    public abstract class TimelinePostCreateRequestContent
    {
        public abstract string TypeName { get; }
    }

    public class TimelinePostCreateRequestTextContent : TimelinePostCreateRequestContent
    {
        private string _text;

        public TimelinePostCreateRequestTextContent(string text)
        {
            if (text is null)
                throw new ArgumentNullException(nameof(text));

            _text = text;
        }

        public override string TypeName => TimelinePostContentTypes.Text;

        public string Text
        {
            get => _text;
            set
            {
                if (value is null)
                    throw new ArgumentNullException(nameof(value));
                _text = value;
            }
        }
    }

    public class TimelinePostCreateRequestImageContent : TimelinePostCreateRequestContent
    {
        private byte[] _data;

        public TimelinePostCreateRequestImageContent(byte[] data)
        {
            if (data is null)
                throw new ArgumentNullException(nameof(data));

            _data = data;
        }

        public override string TypeName => TimelinePostContentTypes.Image;

#pragma warning disable CA1819 // Properties should not return arrays
        public byte[] Data
        {
            get => _data;
            set
            {
                if (value is null)
                    throw new ArgumentNullException(nameof(value));
                _data = value;
            }
        }
#pragma warning restore CA1819 // Properties should not return arrays
    }

    public class TimelinePostCreateRequest
    {
        public TimelinePostCreateRequest(TimelinePostCreateRequestContent content)
        {
            Content = content;
        }

        public string? Color { get; set; }

        /// <summary>If not set, current time is used.</summary>
        public DateTime? Time { get; set; }

        public TimelinePostCreateRequestContent Content { get; set; }
    }

    public class TimelinePostPatchRequest
    {
        public string? Color { get; set; }
        public DateTime? Time { get; set; }
        public TimelinePostCreateRequestContent? Content { get; set; }
    }

    public interface ITimelinePostService
    {
        /// <summary>
        /// Get all the posts in the timeline.
        /// </summary>
        /// <param name="timelineId">The id of the timeline.</param>
        /// <param name="modifiedSince">The time that posts have been modified since.</param>
        /// <param name="includeDeleted">Whether include deleted posts.</param>
        /// <returns>A list of all posts.</returns>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        Task<List<TimelinePostEntity>> GetPosts(long timelineId, DateTime? modifiedSince = null, bool includeDeleted = false);

        /// <summary>
        /// Get a post of a timeline.
        /// </summary>
        /// <param name="timelineId">The id of the timeline of the post.</param>
        /// <param name="postId">The id of the post.</param>
        /// <param name="includeDelete">If true, return the entity even if it is deleted.</param>
        /// <returns>The post.</returns>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when post of <paramref name="postId"/> does not exist or has been deleted.</exception>
        Task<TimelinePostEntity> GetPost(long timelineId, long postId, bool includeDelete = false);

        /// <summary>
        /// Get the etag of data of a post.
        /// </summary>
        /// <param name="timelineId">The id of the timeline of the post.</param>
        /// <param name="postId">The id of the post.</param>
        /// <returns>The etag of the data.</returns>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when post of <paramref name="postId"/> does not exist or has been deleted.</exception>
        /// <exception cref="TimelinePostNoDataException">Thrown when post has no data.</exception>
        Task<string> GetPostDataETag(long timelineId, long postId);

        /// <summary>
        /// Get the data of a post.
        /// </summary>
        /// <param name="timelineId">The id of the timeline of the post.</param>
        /// <param name="postId">The id of the post.</param>
        /// <returns>The etag of the data.</returns>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when post of <paramref name="postId"/> does not exist or has been deleted.</exception>
        /// <exception cref="TimelinePostNoDataException">Thrown when post has no data.</exception>
        /// <seealso cref="GetPostDataETag(long, long)"/>
        Task<PostData> GetPostData(long timelineId, long postId);

        /// <summary>
        /// Create a new post in timeline.
        /// </summary>
        /// <param name="timelineId">The id of the timeline to create post against.</param>
        /// <param name="authorId">The author's user id.</param>
        /// <param name="request">Info about the post.</param>
        /// <returns>The entity of the created post.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="request"/> is null.</exception>
        /// <exception cref="ArgumentException">Thrown when <paramref name="request"/> is of invalid format.</exception>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="UserNotExistException">Thrown if user of <paramref name="authorId"/> does not exist.</exception>
        /// <exception cref="ImageException">Thrown if data is not a image. Validated by <see cref="ImageValidator"/>.</exception>
        Task<TimelinePostEntity> CreatePost(long timelineId, long authorId, TimelinePostCreateRequest request);

        /// <summary>
        /// Modify a post. Change its properties or replace its content.
        /// </summary>
        /// <param name="timelineId">The timeline id.</param>
        /// <param name="postId">The post id.</param>
        /// <param name="request">The request.</param>
        /// <returns>The entity of the patched post.</returns>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="request"/> is null.</exception>
        /// <exception cref="ArgumentException">Thrown when <paramref name="request"/> is of invalid format.</exception>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when post does not exist.</exception>
        /// <exception cref="ImageException">Thrown if data is not a image. Validated by <see cref="ImageValidator"/>.</exception>
        Task<TimelinePostEntity> PatchPost(long timelineId, long postId, TimelinePostPatchRequest request);

        /// <summary>
        /// Delete a post.
        /// </summary>
        /// <param name="timelineId">The id of the timeline to delete post against.</param>
        /// <param name="postId">The id of the post to delete.</param>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when the post with given id does not exist or is deleted already.</exception>
        /// <remarks>
        /// First use <see cref="HasPostModifyPermission(long, long, long, bool)"/> to check the permission.
        /// </remarks>
        Task DeletePost(long timelineId, long postId);

        /// <summary>
        /// Delete all posts of the given user. Used when delete a user.
        /// </summary>
        /// <param name="userId">The id of the user.</param>
        Task DeleteAllPostsOfUser(long userId);

        /// <summary>
        /// Verify whether a user has the permission to modify a post.
        /// </summary>
        /// <param name="timelineId">The id of the timeline.</param>
        /// <param name="postId">The id of the post.</param>
        /// <param name="modifierId">The id of the user to check on.</param>
        /// <param name="throwOnPostNotExist">True if you want it to throw <see cref="TimelinePostNotExistException"/>. Default false.</param>
        /// <returns>True if can modify, false if can't modify.</returns>
        /// <exception cref="TimelineNotExistException">Thrown when timeline does not exist.</exception>
        /// <exception cref="TimelinePostNotExistException">Thrown when the post with given id does not exist or is deleted already and <paramref name="throwOnPostNotExist"/> is true.</exception>
        /// <remarks>
        /// Unless <paramref name="throwOnPostNotExist"/> is true, this method should return true if the post does not exist.
        /// If the post is deleted, its author info still exists, so it is checked as the post is not deleted unless <paramref name="throwOnPostNotExist"/> is true.
        /// 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(long timelineId, long postId, long modifierId, bool throwOnPostNotExist = false);
    }

    public class TimelinePostService : ITimelinePostService
    {
        private readonly ILogger<TimelinePostService> _logger;
        private readonly DatabaseContext _database;
        private readonly IBasicTimelineService _basicTimelineService;
        private readonly IBasicUserService _basicUserService;
        private readonly IDataManager _dataManager;
        private readonly IImageValidator _imageValidator;
        private readonly IClock _clock;
        private readonly ColorValidator _colorValidator = new ColorValidator();

        public TimelinePostService(ILogger<TimelinePostService> logger, DatabaseContext database, IBasicTimelineService basicTimelineService, IBasicUserService basicUserService, IDataManager dataManager, IImageValidator imageValidator, IClock clock)
        {
            _logger = logger;
            _database = database;
            _basicTimelineService = basicTimelineService;
            _basicUserService = basicUserService;
            _dataManager = dataManager;
            _imageValidator = imageValidator;
            _clock = clock;
        }

        private async Task CheckTimelineExistence(long timelineId)
        {
            if (!await _basicTimelineService.CheckExistence(timelineId))
                throw new TimelineNotExistException(timelineId);
        }

        private async Task CheckUserExistence(long userId)
        {
            if (!await _basicUserService.CheckUserExistence(userId))
                throw new UserNotExistException(userId);
        }

        public async Task<List<TimelinePostEntity>> GetPosts(long timelineId, DateTime? modifiedSince = null, bool includeDeleted = false)
        {
            await CheckTimelineExistence(timelineId);

            modifiedSince = modifiedSince?.MyToUtc();

            IQueryable<TimelinePostEntity> query = _database.TimelinePosts.Where(p => p.TimelineId == timelineId);

            if (!includeDeleted)
            {
                query = query.Where(p => p.Content != null);
            }

            if (modifiedSince.HasValue)
            {
                query = query.Where(p => p.LastUpdated >= modifiedSince || (p.Author != null && p.Author.UsernameChangeTime >= modifiedSince));
            }

            query = query.OrderBy(p => p.Time);

            return await query.ToListAsync();
        }

        public async Task<TimelinePostEntity> GetPost(long timelineId, long postId, bool includeDelete = false)
        {
            await CheckTimelineExistence(timelineId);

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

            if (post is null)
            {
                throw new TimelinePostNotExistException(timelineId, postId, false);
            }

            if (!includeDelete && post.Content is null)
            {
                throw new TimelinePostNotExistException(timelineId, postId, true);
            }

            return post;
        }

        public async Task<string> GetPostDataETag(long timelineId, long postId)
        {
            await CheckTimelineExistence(timelineId);

            var postEntity = await _database.TimelinePosts.Where(p => p.TimelineId == timelineId && p.LocalId == postId).SingleOrDefaultAsync();

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

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

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

            var tag = postEntity.Content;

            return tag;
        }

        public async Task<PostData> GetPostData(long timelineId, long postId)
        {
            await CheckTimelineExistence(timelineId);

            var postEntity = await _database.TimelinePosts.Where(p => p.TimelineId == timelineId && p.LocalId == postId).SingleOrDefaultAsync();

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

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

            if (postEntity.ContentType != TimelinePostContentTypes.Image)
                throw new TimelinePostNoDataException(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 PostData
            {
                Data = data,
                Type = postEntity.ExtraContent,
                ETag = tag,
                LastModified = postEntity.LastUpdated
            };
        }

        private async Task SaveContent(TimelinePostEntity entity, TimelinePostCreateRequestContent content)
        {
            switch (content)
            {
                case TimelinePostCreateRequestTextContent c:
                    entity.ContentType = c.TypeName;
                    entity.Content = c.Text;
                    break;
                case TimelinePostCreateRequestImageContent c:
                    var imageFormat = await _imageValidator.Validate(c.Data);
                    var imageFormatText = imageFormat.DefaultMimeType;

                    var tag = await _dataManager.RetainEntry(c.Data);

                    entity.ContentType = content.TypeName;
                    entity.Content = tag;
                    entity.ExtraContent = imageFormatText;
                    break;
                default:
                    throw new ArgumentException("Unknown content type.", nameof(content));
            };
        }

        private async Task CleanContent(TimelinePostEntity entity)
        {
            if (entity.Content is not null && entity.ContentType == TimelinePostContentTypes.Image)
                await _dataManager.FreeEntry(entity.Content);
            entity.Content = null;
        }

        public async Task<TimelinePostEntity> CreatePost(long timelineId, long authorId, TimelinePostCreateRequest request)
        {
            if (request is null)
                throw new ArgumentNullException(nameof(request));


            if (request.Content is null)
                throw new ArgumentException("Content is null.", nameof(request));

            {
                if (!_colorValidator.Validate(request.Color, out var message))
                    throw new ArgumentException("Color is not valid.", nameof(request));
            }

            request.Time = request.Time?.MyToUtc();

            await CheckTimelineExistence(timelineId);
            await CheckUserExistence(authorId);

            var currentTime = _clock.GetCurrentTime();
            var finalTime = request.Time ?? currentTime;

            await using var transaction = await _database.Database.BeginTransactionAsync();

            var postEntity = new TimelinePostEntity
            {
                AuthorId = authorId,
                TimelineId = timelineId,
                Time = finalTime,
                LastUpdated = currentTime,
                Color = request.Color
            };

            await SaveContent(postEntity, request.Content);

            var timelineEntity = await _database.Timelines.Where(t => t.Id == timelineId).SingleAsync();
            timelineEntity.CurrentPostLocalId += 1;
            postEntity.LocalId = timelineEntity.CurrentPostLocalId;

            _database.TimelinePosts.Add(postEntity);

            await _database.SaveChangesAsync();

            await transaction.CommitAsync();

            return postEntity;
        }

        public async Task<TimelinePostEntity> PatchPost(long timelineId, long postId, TimelinePostPatchRequest request)
        {
            if (request is null)
                throw new ArgumentNullException(nameof(request));

            {
                if (!_colorValidator.Validate(request.Color, out var message))
                    throw new ArgumentException("Color is not valid.", nameof(request));
            }

            request.Time = request.Time?.MyToUtc();

            await CheckTimelineExistence(timelineId);

            var entity = await _database.TimelinePosts.Where(p => p.TimelineId == timelineId && p.LocalId == postId).SingleOrDefaultAsync();

            await using var transaction = await _database.Database.BeginTransactionAsync();

            if (entity is null)
                throw new TimelinePostNotExistException(timelineId, postId, false);

            if (entity.Content is null)
                throw new TimelinePostNotExistException(timelineId, postId, true);

            if (request.Time.HasValue)
                entity.Time = request.Time.Value;

            if (request.Color is not null)
                entity.Color = request.Color;

            if (request.Content is not null)
            {
                await CleanContent(entity);
                await SaveContent(entity, request.Content);
            }

            entity.LastUpdated = _clock.GetCurrentTime();

            await _database.SaveChangesAsync();

            await transaction.CommitAsync();

            return entity;
        }

        public async Task DeletePost(long timelineId, long postId)
        {
            await CheckTimelineExistence(timelineId);

            var entity = await _database.TimelinePosts.Where(p => p.TimelineId == timelineId && p.LocalId == postId).SingleOrDefaultAsync();

            if (entity == null)
                throw new TimelinePostNotExistException(timelineId, postId, false);

            if (entity.Content == null)
                throw new TimelinePostNotExistException(timelineId, postId, true);

            await using var transaction = await _database.Database.BeginTransactionAsync();

            await CleanContent(entity);

            entity.LastUpdated = _clock.GetCurrentTime();

            await _database.SaveChangesAsync();

            await transaction.CommitAsync();
        }

        public async Task DeleteAllPostsOfUser(long userId)
        {
            var posts = await _database.TimelinePosts.Where(p => p.AuthorId == userId).ToListAsync();

            var now = _clock.GetCurrentTime();

            var dataTags = new List<string>();

            foreach (var post in posts)
            {
                if (post.Content != null)
                {
                    if (post.ContentType == TimelinePostContentTypes.Image)
                    {
                        dataTags.Add(post.Content);
                    }
                    post.Content = null;
                }
                post.LastUpdated = now;
            }

            await _database.SaveChangesAsync();

            foreach (var dataTag in dataTags)
            {
                await _dataManager.FreeEntry(dataTag);
            }
        }

        public async Task<bool> HasPostModifyPermission(long timelineId, long postId, long modifierId, bool throwOnPostNotExist = false)
        {
            await CheckTimelineExistence(timelineId);

            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 == postId).Select(p => new { p.Content, p.AuthorId }).SingleOrDefaultAsync();

            if (postEntity == null)
            {
                if (throwOnPostNotExist)
                    throw new TimelinePostNotExistException(timelineId, postId, false);
                else
                    return true;
            }

            if (postEntity.Content == null && throwOnPostNotExist)
            {
                throw new TimelinePostNotExistException(timelineId, postId, true);
            }

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