Use original file names for downloaded media

Closes #327

DiscordChatExporter.Domain/Exporting/MediaDownloader.cs

@@ -9,38 +9,44 @@ using DiscordChatExporter.Domain.Internal.Extensions;
 
 namespace DiscordChatExporter.Domain.Exporting
 {
-    internal partial class MediaDownloader
+    internal class MediaDownloader
     {
         private readonly HttpClient _httpClient = Singleton.HttpClient;
         private readonly string _workingDirPath;
 
-        private readonly Dictionary<string, string> _mediaPathMap = new Dictionary<string, string>();
+        private readonly Dictionary<string, string> _pathMap = new Dictionary<string, string>();
 
         public MediaDownloader(string workingDirPath)
         {
             _workingDirPath = workingDirPath;
         }
 
+        private string GetRandomSuffix() => Guid.NewGuid().ToString().Replace("-", "").Substring(0, 8);
+
+        private string GetFileNameFromUrl(string url)
+        {
+            var originalFileName = Regex.Match(url, @".+/([^?]*)").Groups[1].Value;
+
+            if (string.IsNullOrWhiteSpace(originalFileName))
+                return GetRandomSuffix();
+
+            return $"{Path.GetFileNameWithoutExtension(originalFileName)}-{GetRandomSuffix()}{Path.GetExtension(originalFileName)}";
+        }
+
         // HACK: ConfigureAwait() is crucial here to enable sync-over-async in HtmlMessageWriter
         public async ValueTask<string> DownloadAsync(string url)
         {
-            if (_mediaPathMap.TryGetValue(url, out var cachedFilePath))
+            if (_pathMap.TryGetValue(url, out var cachedFilePath))
                 return cachedFilePath;
 
-            var extension = Path.GetExtension(GetFileNameFromUrl(url));
-            var fileName = $"{Guid.NewGuid()}{extension}";
+            var fileName = GetFileNameFromUrl(url);
             var filePath = Path.Combine(_workingDirPath, fileName);
 
             Directory.CreateDirectory(_workingDirPath);
 
             await _httpClient.DownloadAsync(url, filePath).ConfigureAwait(false);
 
-            return _mediaPathMap[url] = filePath;
-        }
+            return _pathMap[url] = filePath;
         }
-
-    internal partial class MediaDownloader
-    {
-        private static string GetFileNameFromUrl(string url) => Regex.Match(url, @".+/([^?]*)").Groups[1].Value;
     }
 }