Refactored archive code into a service so that I can write tests for it.

API/Services/ArchiveService.cs

@@ -0,0 +1,74 @@
+using System.Diagnostics;
+using System.IO;
+using System.IO.Compression;
+using System.Linq;
+using API.Extensions;
+using API.Interfaces;
+using Microsoft.Extensions.Logging;
+
+namespace API.Services
+{
+    /// <summary>
+    /// Responsible for manipulating Archive files. Used by <see cref="CacheService"/> almost exclusively.
+    /// </summary>
+    public class ArchiveService : IArchiveService
+    {
+        private readonly ILogger<ArchiveService> _logger;
+
+        public ArchiveService(ILogger<ArchiveService> logger)
+        {
+            _logger = logger;
+        }
+
+        public bool ArchiveNeedsFlattening(ZipArchive archive)
+        {
+            // Sometimes ZipArchive will list the directory and others it will just keep it in the FullName
+            return archive.Entries.Count > 0 &&
+                !Path.HasExtension(archive.Entries.ElementAt(0).FullName) ||
+                archive.Entries.Any(e => e.FullName.Contains(Path.AltDirectorySeparatorChar));
+            
+            // return archive.Entries.Count > 0 &&
+            //        archive.Entries.Any(e => e.FullName.Contains(Path.AltDirectorySeparatorChar));
+            //return archive.Entries.Count > 0 && !Path.HasExtension(archive.Entries.ElementAt(0).FullName);
+        }
+
+        /// <summary>
+        /// Extracts an archive to a temp cache directory. Returns path to new directory. If temp cache directory already exists,
+        /// will return that without performing an extraction. Returns empty string if there are any invalidations which would
+        /// prevent operations to perform correctly (missing archivePath file, empty archive, etc).
+        /// </summary>
+        /// <param name="archivePath">A valid file to an archive file.</param>
+        /// <param name="extractPath">Path to extract to</param>
+        /// <returns></returns>
+        public void ExtractArchive(string archivePath, string extractPath)
+        {
+            if (!File.Exists(archivePath) || !Parser.Parser.IsArchive(archivePath))
+            {
+                _logger.LogError($"Archive {archivePath} could not be found.");
+                return;
+            }
+
+            if (Directory.Exists(extractPath))
+            {
+                _logger.LogDebug($"Archive {archivePath} has already been extracted. Returning existing folder.");
+                return;
+            }
+           
+            Stopwatch sw = Stopwatch.StartNew();
+            using ZipArchive archive = ZipFile.OpenRead(archivePath);
+            var needsFlattening = ArchiveNeedsFlattening(archive);
+            if (!archive.HasFiles() && !needsFlattening) return;
+            
+            archive.ExtractToDirectory(extractPath);
+            _logger.LogDebug($"Extracted archive to {extractPath} in {sw.ElapsedMilliseconds} milliseconds.");
+
+            if (needsFlattening)
+            {
+                sw = Stopwatch.StartNew();
+                _logger.LogInformation("Extracted archive is nested in root folder, flattening...");
+                new DirectoryInfo(extractPath).Flatten();
+                _logger.LogInformation($"Flattened in {sw.ElapsedMilliseconds} milliseconds");
+            }
+        }
+    }
+}