Kavita/API/Services/CacheService.cs

using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using API.Comparators;
using API.Data;
using API.Entities;
using API.Entities.Enums;
using API.Extensions;
using Microsoft.Extensions.Logging;

namespace API.Services
{
    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>
        /// <returns>Chapter for the passed chapterId. Side-effect from ensuring cache.</returns>
        Task<Chapter> Ensure(int chapterId);
        /// <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);
        string GetCachedPagePath(Chapter chapter, int page);
        string GetCachedEpubFile(int chapterId, Chapter chapter);
        public void ExtractChapterFiles(string extractPath, IReadOnlyList<MangaFile> files);
    }
    public class CacheService : ICacheService
    {
        private readonly ILogger<CacheService> _logger;
        private readonly IUnitOfWork _unitOfWork;
        private readonly IDirectoryService _directoryService;
        private readonly IReadingItemService _readingItemService;
        private readonly NumericComparer _numericComparer;

        public CacheService(ILogger<CacheService> logger, IUnitOfWork unitOfWork,
            IDirectoryService directoryService, IReadingItemService readingItemService)
        {
            _logger = logger;
            _unitOfWork = unitOfWork;
            _directoryService = directoryService;
            _readingItemService = readingItemService;
            _numericComparer = new NumericComparer();
        }

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

        /// <summary>
        /// Caches the files for the given chapter to CacheDirectory
        /// </summary>
        /// <param name="chapterId"></param>
        /// <returns>This will always return the Chapter for the chapterId</returns>
        public async Task<Chapter> Ensure(int chapterId)
        {
            _directoryService.ExistOrCreate(_directoryService.CacheDirectory);
            var chapter = await _unitOfWork.ChapterRepository.GetChapterAsync(chapterId);
            var extractPath = GetCachePath(chapterId);

            if (!_directoryService.Exists(extractPath))
            {
                var files = chapter.Files.ToList();
                ExtractChapterFiles(extractPath, files);
            }

            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>
        /// <returns></returns>
        public void ExtractChapterFiles(string extractPath, IReadOnlyList<MangaFile> files)
        {
            var removeNonImages = true;
            var fileCount = files.Count;
            var extraPath = "";
            var extractDi = _directoryService.FileSystem.DirectoryInfo.FromDirectoryName(extractPath);

            if (files.Count > 0 && files[0].Format == MangaFormat.Image)
            {
                _readingItemService.Extract(files[0].FilePath, extractPath, MangaFormat.Image, files.Count);
                _directoryService.Flatten(extractDi.FullName);
            }

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

                if (file.Format == MangaFormat.Archive)
                {
                    _readingItemService.Extract(file.FilePath, Path.Join(extractPath, extraPath), file.Format);
                }
                else if (file.Format == MangaFormat.Pdf)
                {
                    _readingItemService.Extract(file.FilePath, Path.Join(extractPath, extraPath), file.Format);
                }
                else if (file.Format == MangaFormat.Epub)
                {
                    removeNonImages = false;
                    _directoryService.ExistOrCreate(extractPath);
                    _directoryService.CopyFileToDirectory(files[0].FilePath, extractPath);
                }
            }

            _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.ClearDirectory(GetCachePath(chapter));
            }
        }


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

        /// <summary>
        /// Returns the absolute path of a cached page.
        /// </summary>
        /// <param name="chapter">Chapter entity 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(Chapter chapter, int page)
        {
            // Calculate what chapter the page belongs to
            var path = GetCachePath(chapter.Id);
            var files = _directoryService.GetFilesWithExtension(path, 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.ElementAt(page - 1) : files.ElementAt(page);
        }
    }
}