using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using API.Data;
using API.DTOs.Reader;
using API.Entities;
using API.Entities.Enums;
using API.Extensions;
using Kavita.Common;
using Microsoft.Extensions.Logging;
using NetVips;

namespace API.Services;
#nullable enable

public interface ICacheService
{
    /// <summary>
    /// Ensures the cache is created for the given chapter and if not, will create it. Should be called before any other
    /// cache operations (except cleanup).
    /// </summary>
    /// <param name="chapterId"></param>
    /// <param name="extractPdfToImages">Extracts a PDF into images for a different reading experience</param>
    /// <returns>Chapter for the passed chapterId. Side-effect from ensuring cache.</returns>
    Task<Chapter?> Ensure(int chapterId, bool extractPdfToImages = false);
    /// <summary>
    /// Clears cache directory of all volumes. This can be invoked from deleting a library or a series.
    /// </summary>
    /// <param name="chapterIds">Volumes that belong to that library. Assume the library might have been deleted before this invocation.</param>
    void CleanupChapters(IEnumerable<int> chapterIds);
    void CleanupBookmarks(IEnumerable<int> seriesIds);
    string GetCachedPagePath(int chapterId, int page);
    string GetCachePath(int chapterId);
    string GetBookmarkCachePath(int seriesId);
    IEnumerable<string> GetCachedPages(int chapterId);
    IEnumerable<FileDimensionDto> GetCachedFileDimensions(string cachePath);
    string GetCachedBookmarkPagePath(int seriesId, int page);
    string GetCachedFile(Chapter chapter);
    public void ExtractChapterFiles(string extractPath, IReadOnlyList<MangaFile> files, bool extractPdfImages = false);
    Task<int> CacheBookmarkForSeries(int userId, int seriesId);
    void CleanupBookmarkCache(int seriesId);
}
public class CacheService : ICacheService
{
    private readonly ILogger<CacheService> _logger;
    private readonly IUnitOfWork _unitOfWork;
    private readonly IDirectoryService _directoryService;
    private readonly IReadingItemService _readingItemService;
    private readonly IBookmarkService _bookmarkService;

    private static readonly ConcurrentDictionary<int, SemaphoreSlim> ExtractLocks = new();

    public CacheService(ILogger<CacheService> logger, IUnitOfWork unitOfWork,
        IDirectoryService directoryService, IReadingItemService readingItemService,
        IBookmarkService bookmarkService)
    {
        _logger = logger;
        _unitOfWork = unitOfWork;
        _directoryService = directoryService;
        _readingItemService = readingItemService;
        _bookmarkService = bookmarkService;
    }

    public IEnumerable<string> GetCachedPages(int chapterId)
    {
        var path = GetCachePath(chapterId);
        return _directoryService.GetFilesWithExtension(path, Tasks.Scanner.Parser.Parser.ImageFileExtensions)
            .OrderByNatural(Path.GetFileNameWithoutExtension);
    }

    /// <summary>
    /// For a given path, scan all files (in reading order) and generate File Dimensions for it. Path must exist
    /// </summary>
    /// <param name="cachePath"></param>
    /// <returns></returns>
    public IEnumerable<FileDimensionDto> GetCachedFileDimensions(string cachePath)
    {
        var sw = Stopwatch.StartNew();
        var files = _directoryService.GetFilesWithExtension(cachePath, Tasks.Scanner.Parser.Parser.ImageFileExtensions)
            .OrderByNatural(Path.GetFileNameWithoutExtension)
            .ToArray();

        if (files.Length == 0)
        {
            return ArraySegment<FileDimensionDto>.Empty;
        }

        var dimensions = new List<FileDimensionDto>();
        var originalCacheSize = Cache.MaxFiles;
        try
        {
            Cache.MaxFiles = 0;
            for (var i = 0; i < files.Length; i++)
            {
                var file = files[i];
                using var image = Image.NewFromFile(file, memory: false, access: Enums.Access.SequentialUnbuffered);
                dimensions.Add(new FileDimensionDto()
                {
                    PageNumber = i,
                    Height = image.Height,
                    Width = image.Width,
                    IsWide = image.Width > image.Height,
                    FileName = file.Replace(cachePath, string.Empty)
                });
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "There was an error calculating image dimensions for {CachePath}", cachePath);
        }
        finally
        {
            Cache.MaxFiles = originalCacheSize;
        }

        _logger.LogDebug("File Dimensions call for {Length} images took {Time}ms", dimensions.Count, sw.ElapsedMilliseconds);
        return dimensions;
    }

    public string GetCachedBookmarkPagePath(int seriesId, int page)
    {
        // Calculate what chapter the page belongs to
        var path = GetBookmarkCachePath(seriesId);
        var files = _directoryService.GetFilesWithExtension(path, Tasks.Scanner.Parser.Parser.ImageFileExtensions);
        files = files
            .AsEnumerable()
            .OrderByNatural(Path.GetFileNameWithoutExtension)
            .ToArray();

        if (files.Length == 0)
        {
            return string.Empty;
        }

        // Since array is 0 based, we need to keep that in account (only affects last image)
        return page == files.Length ? files[page - 1] : files[page];
    }

    /// <summary>
    /// Returns the full path to the cached file. If the file does not exist, will fallback to the original.
    /// </summary>
    /// <param name="chapter"></param>
    /// <returns></returns>
    public string GetCachedFile(Chapter chapter)
    {
        var extractPath = GetCachePath(chapter.Id);
        var path = Path.Join(extractPath, _directoryService.FileSystem.Path.GetFileName(chapter.Files.First().FilePath));
        if (!(_directoryService.FileSystem.FileInfo.New(path).Exists))
        {
            path = chapter.Files.First().FilePath;
        }
        return path;
    }


    /// <summary>
    /// Caches the files for the given chapter to CacheDirectory
    /// </summary>
    /// <param name="chapterId"></param>
    /// <param name="extractPdfToImages">Defaults to false. Extract pdf file into images rather than copying just the pdf file</param>
    /// <returns>This will always return the Chapter for the chapterId</returns>
    public async Task<Chapter?> Ensure(int chapterId, bool extractPdfToImages = false)
    {
        _directoryService.ExistOrCreate(_directoryService.CacheDirectory);
        var chapter = await _unitOfWork.ChapterRepository.GetChapterAsync(chapterId);
        var extractPath = GetCachePath(chapterId);

        SemaphoreSlim extractLock = ExtractLocks.GetOrAdd(chapterId, id => new SemaphoreSlim(1,1));

        await extractLock.WaitAsync();
        try {
            if(_directoryService.Exists(extractPath)) return chapter;

            var files = chapter?.Files.ToList();
            ExtractChapterFiles(extractPath, files, extractPdfToImages);
        } finally {
            extractLock.Release();
        }

        return chapter;
    }

    /// <summary>
    /// This is an internal method for cache service for extracting chapter files to disk. The code is structured
    /// for cache service, but can be re-used (download bookmarks)
    /// </summary>
    /// <param name="extractPath"></param>
    /// <param name="files"></param>
    /// <param name="extractPdfImages">Defaults to false, if true, will extract the images from the PDF renderer and not move the pdf file</param>
    /// <returns></returns>
    public void ExtractChapterFiles(string extractPath, IReadOnlyList<MangaFile>? files, bool extractPdfImages = false)
    {
        if (files == null) return;
        var removeNonImages = true;
        var fileCount = files.Count;
        var extraPath = string.Empty;
        var extractDi = _directoryService.FileSystem.DirectoryInfo.New(extractPath);

        if (files.Count > 0 && files[0].Format == MangaFormat.Image)
        {
            // Check if all the files are Images. If so, do a directory copy, else do the normal copy
            if (files.All(f => f.Format == MangaFormat.Image))
            {
                _directoryService.ExistOrCreate(extractPath);
                _directoryService.CopyFilesToDirectory(files.Select(f => f.FilePath), extractPath);
            }
            else
            {
                foreach (var file in files)
                {
                    if (fileCount > 1)
                    {
                        extraPath = file.Id + string.Empty;
                    }
                    _readingItemService.Extract(file.FilePath, Path.Join(extractPath, extraPath), MangaFormat.Image, files.Count);
                }
                _directoryService.Flatten(extractDi.FullName);
            }

        }

        foreach (var file in files)
        {
            if (fileCount > 1)
            {
                extraPath = file.Id + string.Empty;
            }

            switch (file.Format)
            {
                case MangaFormat.Archive:
                    _readingItemService.Extract(file.FilePath, Path.Join(extractPath, extraPath), file.Format);
                    break;
                case MangaFormat.Epub:
                case MangaFormat.Pdf:
                {
                    if (!_directoryService.FileSystem.File.Exists(files[0].FilePath))
                    {
                        _logger.LogError("{File} does not exist on disk", files[0].FilePath);
                        throw new KavitaException($"{files[0].FilePath} does not exist on disk");
                    }
                    if (extractPdfImages)
                    {
                        _readingItemService.Extract(file.FilePath, Path.Join(extractPath, extraPath), file.Format);
                        break;
                    }
                    removeNonImages = false;

                    _directoryService.ExistOrCreate(extractPath);
                    _directoryService.CopyFileToDirectory(files[0].FilePath, extractPath);
                    break;
                }
            }
        }

        _directoryService.Flatten(extractDi.FullName);
        if (removeNonImages)
        {
            _directoryService.RemoveNonImages(extractDi.FullName);
        }
    }

    /// <summary>
    /// Removes the cached files and folders for a set of chapterIds
    /// </summary>
    /// <param name="chapterIds"></param>
    public void CleanupChapters(IEnumerable<int> chapterIds)
    {
        foreach (var chapter in chapterIds)
        {
            _directoryService.ClearAndDeleteDirectory(GetCachePath(chapter));
        }
    }

    /// <summary>
    /// Removes the cached files and folders for a set of chapterIds
    /// </summary>
    /// <param name="seriesIds"></param>
    public void CleanupBookmarks(IEnumerable<int> seriesIds)
    {
        foreach (var series in seriesIds)
        {
            _directoryService.ClearAndDeleteDirectory(GetBookmarkCachePath(series));
        }
    }


    /// <summary>
    /// Returns the cache path for a given Chapter. Should be cacheDirectory/{chapterId}/
    /// </summary>
    /// <param name="chapterId"></param>
    /// <returns></returns>
    public string GetCachePath(int chapterId)
    {
        return _directoryService.FileSystem.Path.GetFullPath(_directoryService.FileSystem.Path.Join(_directoryService.CacheDirectory, $"{chapterId}/"));
    }

    /// <summary>
    /// Returns the cache path for a given series' bookmarks. Should be cacheDirectory/{seriesId_bookmarks}/
    /// </summary>
    /// <param name="seriesId"></param>
    /// <returns></returns>
    public string GetBookmarkCachePath(int seriesId)
    {
        return _directoryService.FileSystem.Path.GetFullPath(_directoryService.FileSystem.Path.Join(_directoryService.CacheDirectory, $"{seriesId}_bookmarks/"));
    }

    /// <summary>
    /// Returns the absolute path of a cached page.
    /// </summary>
    /// <param name="chapterId">Chapter id with Files populated.</param>
    /// <param name="page">Page number to look for</param>
    /// <returns>Page filepath or empty if no files found.</returns>
    public string GetCachedPagePath(int chapterId, int page)
    {
        // Calculate what chapter the page belongs to
        var path = GetCachePath(chapterId);
        // NOTE: We can optimize this by extracting and renaming, so we don't need to scan for the files and can do a direct access
        var files = _directoryService.GetFilesWithExtension(path, Tasks.Scanner.Parser.Parser.ImageFileExtensions)
            //.OrderByNatural(Path.GetFileNameWithoutExtension) // This is already done in GetPageFromFiles
            .ToArray();

        return GetPageFromFiles(files, page);
    }

    public async Task<int> CacheBookmarkForSeries(int userId, int seriesId)
    {
        var destDirectory = _directoryService.FileSystem.Path.Join(_directoryService.CacheDirectory, seriesId + "_bookmarks");
        if (_directoryService.Exists(destDirectory)) return _directoryService.GetFiles(destDirectory).Count();

        var bookmarkDtos = await _unitOfWork.UserRepository.GetBookmarkDtosForSeries(userId, seriesId);
        var files = (await _bookmarkService.GetBookmarkFilesById(bookmarkDtos.Select(b => b.Id))).ToList();
        _directoryService.CopyFilesToDirectory(files, destDirectory,
            Enumerable.Range(1, files.Count).Select(i => i + string.Empty).ToList());
        return files.Count;
    }

    /// <summary>
    /// Clears a cached bookmarks for a series id folder
    /// </summary>
    /// <param name="seriesId"></param>
    public void CleanupBookmarkCache(int seriesId)
    {
        var destDirectory = _directoryService.FileSystem.Path.Join(_directoryService.CacheDirectory, seriesId + "_bookmarks");
        if (!_directoryService.Exists(destDirectory)) return;

        _directoryService.ClearAndDeleteDirectory(destDirectory);
    }

    /// <summary>
    /// Returns either the file or an empty string
    /// </summary>
    /// <param name="files"></param>
    /// <param name="pageNum"></param>
    /// <returns></returns>
    public static string GetPageFromFiles(string[] files, int pageNum)
    {
        files = files
            .AsEnumerable()
            .OrderByNatural(Path.GetFileNameWithoutExtension)
            .ToArray();

        if (files.Length == 0)
        {
            return string.Empty;
        }

        if (pageNum < 0)
        {
            pageNum = 0;
        }

        // Since array is 0 based, we need to keep that in account (only affects last image)
        return pageNum >= files.Length ? files[Math.Min(pageNum - 1, files.Length - 1)] : files[pageNum];
    }


}