Added a basic cache service to handle interations with the underlying cache implementation. Refactored some code to be more robust.

API/Services/CacheService.cs

@@ -0,0 +1,46 @@
+using System.IO;
+using API.Entities;
+using API.Interfaces;
+
+namespace API.Services
+{
+    public class CacheService : ICacheService
+    {
+        private readonly IDirectoryService _directoryService;
+        private readonly ISeriesRepository _seriesRepository;
+
+        public CacheService(IDirectoryService directoryService, ISeriesRepository seriesRepository)
+        {
+            _directoryService = directoryService;
+            _seriesRepository = seriesRepository;
+        }
+
+        public async void Ensure(int volumeId)
+        {
+            Volume volume = await _seriesRepository.GetVolumeAsync(volumeId);
+            foreach (var file in volume.Files)
+            {
+                var extractPath = GetCachePath(volumeId);
+                if (file.Chapter > 0)
+                {
+                    extractPath = Path.Join(extractPath, file.Chapter + "");
+                }
+                
+                _directoryService.ExtractArchive(file.FilePath, extractPath);
+            }
+        }
+
+        public bool Cleanup(Volume volume)
+        {
+            throw new System.NotImplementedException();
+        }
+
+        public string GetCachePath(int volumeId)
+        {
+            // TODO: Make this an absolute path, no ..'s in it.
+            return Path.Join(Directory.GetCurrentDirectory(), $"../cache/{volumeId}/");
+        }
+        
+        
+    }
+}