using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using ErsatzTV.Core;
using ErsatzTV.Core.Domain;
using ErsatzTV.Core.Interfaces.Metadata;
using ErsatzTV.Core.Interfaces.Repositories;
using ErsatzTV.Core.Interfaces.Search;
using ErsatzTV.Core.Search;
using LanguageExt;
using LanguageExt.UnsafeValueAccess;
using Lucene.Net.Analysis.Standard;
using Lucene.Net.Documents;
using Lucene.Net.Index;
using Lucene.Net.QueryParsers.Classic;
using Lucene.Net.Sandbox.Queries;
using Lucene.Net.Search;
using Lucene.Net.Store;
using Lucene.Net.Util;
using Query = Lucene.Net.Search.Query;

namespace ErsatzTV.Infrastructure.Search
{
    public class SearchIndex : ISearchIndex
    {
        private const LuceneVersion AppLuceneVersion = LuceneVersion.LUCENE_48;

        private const string IdField = "id";
        private const string TypeField = "type";
        private const string TitleField = "title";
        private const string SortTitleField = "sort_title";
        private const string GenreField = "genre";
        private const string TagField = "tag";
        private const string PlotField = "plot";
        private const string LibraryNameField = "library_name";
        private const string TitleAndYearField = "title_and_year";
        private const string JumpLetterField = "jump_letter";

        private const string MovieType = "movie";
        private const string ShowType = "show";

        private static bool _isRebuilding;

        private readonly ILocalFileSystem _localFileSystem;

        private readonly string[] _searchFields = { TitleField, GenreField, TagField };
        private readonly ISearchRepository _searchRepository;

        public SearchIndex(ILocalFileSystem localFileSystem, ISearchRepository searchRepository)
        {
            _localFileSystem = localFileSystem;
            _searchRepository = searchRepository;
        }

        public int Version => 1;

        public Task<bool> Initialize()
        {
            _localFileSystem.EnsureFolderExists(FileSystemLayout.SearchIndexFolder);
            return Task.FromResult(true);
        }

        public async Task<Unit> Rebuild(List<int> itemIds)
        {
            _isRebuilding = true;

            await Initialize();

            using var dir = FSDirectory.Open(FileSystemLayout.SearchIndexFolder);
            var analyzer = new StandardAnalyzer(AppLuceneVersion);
            var indexConfig = new IndexWriterConfig(AppLuceneVersion, analyzer) { OpenMode = OpenMode.CREATE };
            using var writer = new IndexWriter(dir, indexConfig);

            foreach (int id in itemIds)
            {
                Option<MediaItem> maybeMediaItem = await _searchRepository.GetItemToIndex(id);
                if (maybeMediaItem.IsSome)
                {
                    MediaItem mediaItem = maybeMediaItem.ValueUnsafe();
                    switch (mediaItem)
                    {
                        case Movie movie:
                            UpdateMovie(movie, writer);
                            break;
                        case Show show:
                            UpdateShow(show, writer);
                            break;
                    }
                }
            }

            _isRebuilding = false;

            return Unit.Default;
        }

        public Task<Unit> AddItems(List<MediaItem> items) => UpdateItems(items);

        public Task<Unit> UpdateItems(List<MediaItem> items)
        {
            using var dir = FSDirectory.Open(FileSystemLayout.SearchIndexFolder);
            var analyzer = new StandardAnalyzer(AppLuceneVersion);
            var indexConfig = new IndexWriterConfig(AppLuceneVersion, analyzer) { OpenMode = OpenMode.APPEND };
            using var writer = new IndexWriter(dir, indexConfig);

            foreach (MediaItem item in items)
            {
                switch (item)
                {
                    case Movie movie:
                        UpdateMovie(movie, writer);
                        break;
                    case Show show:
                        UpdateShow(show, writer);
                        break;
                }
            }

            return Task.FromResult(Unit.Default);
        }

        public Task<Unit> RemoveItems(List<int> ids)
        {
            using var dir = FSDirectory.Open(FileSystemLayout.SearchIndexFolder);
            var analyzer = new StandardAnalyzer(AppLuceneVersion);
            var indexConfig = new IndexWriterConfig(AppLuceneVersion, analyzer) { OpenMode = OpenMode.APPEND };
            using var writer = new IndexWriter(dir, indexConfig);

            foreach (int id in ids)
            {
                writer.DeleteDocuments(new Term(IdField, id.ToString()));
            }

            return Task.FromResult(Unit.Default);
        }

        public Task<SearchResult> Search(string searchQuery, int skip, int limit, string searchField = "")
        {
            if (_isRebuilding ||
                string.IsNullOrWhiteSpace(searchQuery.Replace("*", string.Empty).Replace("?", string.Empty)))
            {
                return new SearchResult(new List<SearchItem>(), 0).AsTask();
            }

            using var dir = FSDirectory.Open(FileSystemLayout.SearchIndexFolder);
            using var reader = DirectoryReader.Open(dir);
            var searcher = new IndexSearcher(reader);
            int hitsLimit = skip + limit;
            using var analyzer = new StandardAnalyzer(AppLuceneVersion);
            QueryParser parser = !string.IsNullOrWhiteSpace(searchField)
                ? new QueryParser(AppLuceneVersion, searchField, analyzer)
                : new MultiFieldQueryParser(AppLuceneVersion, _searchFields, analyzer);
            Query query = ParseQuery(searchQuery, parser);
            var filter = new DuplicateFilter(TitleAndYearField);
            var sort = new Sort(new SortField(SortTitleField, SortFieldType.STRING));
            TopFieldDocs topDocs = searcher.Search(query, filter, hitsLimit, sort, true, true);
            IEnumerable<ScoreDoc> selectedHits = topDocs.ScoreDocs.Skip(skip).Take(limit);

            var searchResult = new SearchResult(
                selectedHits.Map(d => ProjectToSearchItem(searcher.Doc(d.Doc))).ToList(),
                topDocs.TotalHits);

            searchResult.PageMap = GetSearchPageMap(searcher, query, filter, sort, limit);

            return searchResult.AsTask();
        }

        private static Option<SearchPageMap> GetSearchPageMap(
            IndexSearcher searcher,
            Query query,
            DuplicateFilter filter,
            Sort sort,
            int limit)
        {
            ScoreDoc[] allDocs = searcher.Search(query, filter, int.MaxValue, sort, true, true).ScoreDocs;
            var letters = new List<char>
            {
                '#', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                'u', 'v', 'w', 'x', 'y', 'z'
            };
            var map = letters.ToDictionary(letter => letter, _ => 0);

            var current = 0;
            var page = 0;
            while (current < allDocs.Length)
            {
                // walk up by page size (limit)
                page++;
                current += limit;
                if (current > allDocs.Length)
                {
                    current = allDocs.Length;
                }

                char jumpLetter = searcher.Doc(allDocs[current - 1].Doc).Get(JumpLetterField).Head();
                foreach (char letter in letters.Where(l => letters.IndexOf(l) <= letters.IndexOf(jumpLetter)))
                {
                    if (map[letter] == 0)
                    {
                        map[letter] = page;
                    }
                }
            }

            int max = map.Values.Max();
            foreach (char letter in letters.Where(letter => map[letter] == 0))
            {
                map[letter] = max;
            }

            return new SearchPageMap(map);
        }

        private static void UpdateMovie(Movie movie, IndexWriter writer)
        {
            Option<MovieMetadata> maybeMetadata = movie.MovieMetadata.HeadOrNone();
            if (maybeMetadata.IsSome)
            {
                MovieMetadata metadata = maybeMetadata.ValueUnsafe();

                var doc = new Document
                {
                    new StringField(IdField, movie.Id.ToString(), Field.Store.YES),
                    new StringField(TypeField, MovieType, Field.Store.NO),
                    new TextField(TitleField, metadata.Title, Field.Store.NO),
                    new StringField(SortTitleField, metadata.SortTitle.ToLowerInvariant(), Field.Store.NO),
                    new TextField(LibraryNameField, movie.LibraryPath.Library.Name, Field.Store.NO),
                    new StringField(TitleAndYearField, GetTitleAndYear(metadata), Field.Store.NO),
                    new StringField(JumpLetterField, GetJumpLetter(metadata), Field.Store.YES)
                };

                if (!string.IsNullOrWhiteSpace(metadata.Plot))
                {
                    doc.Add(new TextField(PlotField, metadata.Plot ?? string.Empty, Field.Store.NO));
                }

                foreach (Genre genre in metadata.Genres)
                {
                    doc.Add(new TextField(GenreField, genre.Name, Field.Store.NO));
                }

                foreach (Tag tag in metadata.Tags)
                {
                    doc.Add(new TextField(TagField, tag.Name, Field.Store.NO));
                }

                writer.UpdateDocument(new Term(IdField, movie.Id.ToString()), doc);
            }
        }

        private static void UpdateShow(Show show, IndexWriter writer)
        {
            Option<ShowMetadata> maybeMetadata = show.ShowMetadata.HeadOrNone();
            if (maybeMetadata.IsSome)
            {
                ShowMetadata metadata = maybeMetadata.ValueUnsafe();

                var doc = new Document
                {
                    new StringField(IdField, show.Id.ToString(), Field.Store.YES),
                    new StringField(TypeField, ShowType, Field.Store.NO),
                    new TextField(TitleField, metadata.Title, Field.Store.NO),
                    new StringField(SortTitleField, metadata.SortTitle.ToLowerInvariant(), Field.Store.NO),
                    new TextField(LibraryNameField, show.LibraryPath.Library.Name, Field.Store.NO),
                    new StringField(TitleAndYearField, GetTitleAndYear(metadata), Field.Store.NO),
                    new StringField(JumpLetterField, GetJumpLetter(metadata), Field.Store.YES)
                };

                if (!string.IsNullOrWhiteSpace(metadata.Plot))
                {
                    doc.Add(new TextField(PlotField, metadata.Plot ?? string.Empty, Field.Store.NO));
                }

                foreach (Genre genre in metadata.Genres)
                {
                    doc.Add(new TextField(GenreField, genre.Name, Field.Store.NO));
                }

                foreach (Tag tag in metadata.Tags)
                {
                    doc.Add(new TextField(TagField, tag.Name, Field.Store.NO));
                }

                writer.UpdateDocument(new Term(IdField, show.Id.ToString()), doc);
            }
        }

        private SearchItem ProjectToSearchItem(Document doc) => new(Convert.ToInt32(doc.Get(IdField)));

        private Query ParseQuery(string searchQuery, QueryParser parser)
        {
            Query query;
            try
            {
                query = parser.Parse(searchQuery.Trim());
            }
            catch (ParseException)
            {
                query = parser.Parse(QueryParserBase.Escape(searchQuery.Trim()));
            }

            return query;
        }

        private static string GetTitleAndYear(Metadata metadata) =>
            $"{metadata.Title}_{metadata.Year}";

        private static string GetJumpLetter(Metadata metadata)
        {
            char c = metadata.SortTitle.ToLowerInvariant().Head();
            return c switch
            {
                (>= 'a' and <= 'z') => c.ToString(),
                _ => "#"
            };
        }
    }
}