using Serilog;
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Caching.Memory;
using NadekoBot.Common;
using NadekoBot.Extensions;
using NadekoBot.Services;

namespace NadekoBot.Modules.Nsfw.Common
{
    public class SearchImageCacher : INService
    {
        private readonly IHttpClientFactory _httpFactory;
        private readonly SemaphoreSlim _lock = new SemaphoreSlim(1, 1);
        private readonly Random _rng;

        private static readonly ISet<string> defaultTagBlacklist = new HashSet<string>()
        {
            "loli",
            "lolicon",
            "shota",
            "shotacon",
            "cub"
        };

        private readonly Dictionary<Booru, object> _typeLocks = new();
        private readonly Dictionary<Booru, HashSet<string>> _usedTags = new();
        private readonly IMemoryCache _cache;

        public SearchImageCacher(IHttpClientFactory httpFactory, IMemoryCache cache)
        {
            _httpFactory = httpFactory;
            _rng = new NadekoRandom();
            _cache = cache;

            // initialize new cache with empty values
            foreach (var type in Enum.GetValues<Booru>())
            {
                _typeLocks[type] = new();
                _usedTags[type] = new();
            }
        }

        private string Key(Booru boory, string tag)
            => $"booru:{boory}__tag:{tag}";

        /// <summary>
        /// Download images of the specified type, and cache them.
        /// </summary>
        /// <param name="tags">Required tags</param>
        /// <param name="forceExplicit">Whether images will be forced to be explicit</param>
        /// <param name="type">Provider type</param>
        /// <param name="cancel">Cancellation token</param>
        /// <returns>Whether any image is found.</returns>
        private async Task<bool> UpdateImagesInternalAsync(string[] tags, bool forceExplicit, Booru type, CancellationToken cancel)
        {
            var images = await DownloadImagesAsync(tags, forceExplicit, type, cancel).ConfigureAwait(false);
            if (images is null || images.Count == 0)
            {
                // Log.Warning("Got no images for {0}, tags: {1}", type, string.Join(", ", tags));
                return false;
            }

            Log.Information("Updating {0}...", type);
            lock (_typeLocks[type])
            {
                var typeUsedTags = _usedTags[type];
                foreach (var tag in tags)
                    typeUsedTags.Add(tag);

                // if user uses no tags for the hentai command and there are no used
                // tags atm, just select 50 random tags from downloaded images to seed
                if (typeUsedTags.Count == 0)
                    images.SelectMany(x => x.Tags)
                        .Distinct()
                        .Shuffle()
                        .Take(50)
                        .ForEach(x => typeUsedTags.Add(x));

                foreach (var img in images)
                {
                    // if any of the tags is a tag banned by discord
                    // do not put that image in the cache
                    if (defaultTagBlacklist.Overlaps(img.Tags))
                        continue;
                    
                    // if image doesn't have a proper absolute uri, skip it
                    if (!Uri.IsWellFormedUriString(img.FileUrl, UriKind.Absolute))
                        continue;

                    // i'm appending current tags because of tag aliasing
                    // this way, if user uses tag alias, for example 'kissing' -
                    // both 'kiss' (real tag returned by the image) and 'kissing' will be populated with
                    // retreived images
                    foreach (var tag in img.Tags.Concat(tags).Distinct())
                    {
                        if (typeUsedTags.Contains(tag))
                        {
                            var set = _cache.GetOrCreate<HashSet<ImageData>>(Key(type, tag), e =>
                            {
                                e.AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(30);
                                return new();
                            });
                            
                            if(set.Count < 100)
                                set.Add(img);
                        }
                    }
                }
            }

            return true;
        }

        private ImageData QueryLocal(string[] tags, bool forceExplicit, Booru type, HashSet<string> blacklistedTags)
        {
            var setList = new List<HashSet<ImageData>>();

            // ofc make sure no changes are happening while we're getting a random one
            lock (_typeLocks[type])
            {
                // if no tags are provided, get a random tag
                if (tags.Length == 0)
                {
                    // get all tags in the cache
                    if (_usedTags.TryGetValue(type, out var allTags)
                        && allTags.Count > 0)
                    {
                        tags = new[] {allTags.ToList()[_rng.Next(0, allTags.Count)]};
                    }
                    else
                    {
                        return null;
                    }
                }

                foreach (var tag in tags)
                {
                    // if any tag is missing from cache, that means there is no result
                    if (_cache.TryGetValue<HashSet<ImageData>>(Key(type, tag), out var set))
                        setList.Add(set);
                    else
                        return null;
                }

                if (setList.Count == 0)
                    return null;


                List<ImageData> resultList;
                // if multiple tags, we need to interesect sets
                if (setList.Count > 1)
                {
                    // now that we have sets, interesect them to find eligible items
                    // make a copy of the 1st set
                    var resultSet = new HashSet<ImageData>(setList[0]);

                    // go through all other sets, and
                    for (var i = 1; i < setList.Count; ++i)
                    {
                        // if any of the elements in result set are not present in the current set
                        // remove it from the result set
                        resultSet.IntersectWith(setList[i]);
                    }

                    resultList = resultSet.ToList();

                }
                else
                {
                    // if only one tag, use that set
                    resultList = setList[0].ToList();
                }

                // return a random one which doesn't have blacklisted tags in it
                resultList = resultList.Where(x => !blacklistedTags.Overlaps(x.Tags)).ToList();

                // if no items in the set -> not found
                if (resultList.Count == 0)
                    return null;
                
                var toReturn = resultList[_rng.Next(0, resultList.Count)];

                // remove from cache
                foreach (var tag in tags)
                {
                    if (_cache.TryGetValue<HashSet<ImageData>>(Key(type, tag), out var items))
                    {
                        items.Remove(toReturn);
                    }
                }
                return toReturn;
            }
        }

        public async Task<ImageData> GetImageNew(string[] tags, bool forceExplicit, Booru type,
            HashSet<string> blacklistedTags, CancellationToken cancel)
        {
            // make sure tags are proper
            tags = tags
                .Where(x => x is not null)
                .Select(tag => tag.ToLowerInvariant().Trim())
                .Distinct()
                .ToArray();

            if (tags.Length > 2 && type == Booru.Danbooru)
                tags = tags[..2];

            // use both tags banned by discord and tags banned on the server 
            if (blacklistedTags.Overlaps(tags) || defaultTagBlacklist.Overlaps(tags))
                return default;

            // query for an image
            var image = QueryLocal(tags, forceExplicit, type, blacklistedTags);
            if (image is not null)
                return image;

            var success = false;
            try
            {
                // if image is not found, update the cache and query again
                success = await UpdateImagesInternalAsync(tags, forceExplicit, type, cancel).ConfigureAwait(false);
            }
            catch (HttpRequestException)
            {
                return default;
            }

            if (!success)
                return default;
            image = QueryLocal(tags, forceExplicit, type, blacklistedTags);

            return image;
        }

        private readonly ConcurrentDictionary<(Booru, string), int> maxPages = new();

        public async Task<List<ImageData>> DownloadImagesAsync(string[] tags, bool isExplicit, Booru type, CancellationToken cancel)
        {
            var tagStr = string.Join(' ', tags.OrderByDescending(x => x));
            var page = 0;

            var attempt = 0;
            while (attempt++ <= 10)
            {
                if (maxPages.TryGetValue((type, tagStr), out var maxPage))
                {
                    if (maxPage == 0)
                    {
                        Log.Information("Tag {0} yields no result on {1}, skipping.", tagStr, type);
                        return new();
                    }

                    page = _rng.Next(0, maxPage);
                }
                else
                {
                    page = _rng.Next(0, 11);
                }

                var result = await DownloadImagesAsync(tags, isExplicit, type, page, cancel).ConfigureAwait(false);

                if (result is null or { Count: 0 })
                {
                    Log.Information("Tag {0}, page {1} has no result on {2}.", string.Join(", ", tags), page, type.ToString());
                    continue;
                }

                return result;
            }

            return new();
        }

        private IImageDownloader GetImageDownloader(Booru booru, HttpClient http)
            => booru switch
            {
                Booru.Danbooru => new DanbooruImageDownloader(http),
                Booru.Yandere => new YandereImageDownloader(http),
                Booru.Konachan => new KonachanImageDownloader(http),
                Booru.Safebooru => new SafebooruImageDownloader(http),
                Booru.E621 => new E621ImageDownloader(http),
                Booru.Derpibooru => new DerpibooruImageDownloader(http),
                Booru.Gelbooru => new GelbooruImageDownloader(http),
                Booru.Rule34 => new Rule34ImageDownloader(http),
                Booru.Sankaku => new SankakuImageDownloader(http),
                _ => throw new NotImplementedException($"{booru} downloader not implemented.")
            };

        private async Task<List<ImageData>> DownloadImagesAsync(string[] tags, bool isExplicit, Booru type, int page, CancellationToken cancel)
        {
            try
            {
                Log.Information("Downloading from {0} (page {1})...", type, page);

                using var http = _httpFactory.CreateClient();
                var downloader = GetImageDownloader(type, http);

                var images = await downloader.DownloadImageDataAsync(tags, page, isExplicit, cancel);
                if (images.Count == 0)
                {
                    var tagStr = string.Join(' ', tags.OrderByDescending(x => x));
                    maxPages[(type, tagStr)] = page;
                }

                return images;
            }
            catch (OperationCanceledException)
            {
                throw;
            }
            catch (Exception ex)
            {
                Log.Error(ex, "Error downloading an image:\nTags: {0}\nType: {1}\nPage: {2}\nMessage: {3}",
                    string.Join(", ", tags),
                    type,
                    page,
                    ex.Message);
                return new();
            }
        }
    }
}