diff --git a/src/library/library.cr b/src/library/library.cr
index 7c9c020..210912f 100644
--- a/src/library/library.cr
+++ b/src/library/library.cr
@@ -1,9 +1,38 @@
 class Library
+  struct ThumbnailContext
+    property current : Int32, total : Int32
+
+    def initialize
+      @current = 0
+      @total = 0
+    end
+
+    def progress
+      if total == 0
+        0
+      else
+        current / total
+      end
+    end
+
+    def reset
+      @current = 0
+      @total = 0
+    end
+
+    def increment
+      @current += 1
+    end
+  end
+
   include YAML::Serializable
 
   getter dir : String, title_ids : Array(String),
     title_hash : Hash(String, Title)
 
+  @[YAML::Field(ignore: true)]
+  getter thumbnail_ctx = ThumbnailContext.new
+
   use_default
 
   def save_instance
@@ -55,9 +84,6 @@ class Library
     @title_ids = [] of String
     @title_hash = {} of String => Title
 
-    @entries_count = 0
-    @thumbnails_count = 0
-
     register_jobs
   end
 
@@ -278,34 +304,29 @@ class Library
       .shuffle!
   end
 
-  def thumbnail_generation_progress
-    return 0 if @entries_count == 0
-    @thumbnails_count / @entries_count
-  end
-
   def generate_thumbnails
-    if @thumbnails_count > 0
+    if thumbnail_ctx.current > 0
       Logger.debug "Thumbnail generation in progress"
       return
     end
 
     Logger.info "Starting thumbnail generation"
     entries = deep_titles.flat_map(&.deep_entries).reject &.err_msg
-    @entries_count = entries.size
-    @thumbnails_count = 0
+    thumbnail_ctx.total = entries.size
+    thumbnail_ctx.current = 0
 
     # Report generation progress regularly
     spawn do
       loop do
-        unless @thumbnails_count == 0
+        unless thumbnail_ctx.current == 0
           Logger.debug "Thumbnail generation progress: " \
-                       "#{(thumbnail_generation_progress * 100).round 1}%"
+                       "#{(thumbnail_ctx.progress * 100).round 1}%"
         end
         # Generation is completed. We reset the count to 0 to allow subsequent
         #   calls to the function, and break from the loop to stop the progress
         #   report fiber
-        if thumbnail_generation_progress.to_i == 1
-          @thumbnails_count = 0
+        if thumbnail_ctx.progress.to_i == 1
+          thumbnail_ctx.reset
           break
         end
         sleep 10.seconds
@@ -319,7 +340,7 @@ class Library
         #   and CPU
         sleep 1.seconds
       end
-      @thumbnails_count += 1
+      thumbnail_ctx.increment
     end
     Logger.info "Thumbnail generation finished"
   end
diff --git a/src/routes/api.cr b/src/routes/api.cr
index 28ec314..413c318 100644
--- a/src/routes/api.cr
+++ b/src/routes/api.cr
@@ -240,7 +240,7 @@ struct APIRouter
     }
     get "/api/admin/thumbnail_progress" do |env|
       send_json env, {
-        "progress" => Library.default.thumbnail_generation_progress,
+        "progress" => Library.default.thumbnail_ctx.progress,
       }.to_json
     end