StorageManager: remove Post-specific code.

Refactor StorageManager to remove all image URL generation code. Instead
the image URL generation code lives in MediaAsset.

Now StorageManager is only concerned with how to read and write files to
remote storage backends like S3 or SFTP, not with how image URLs should
be generated. This way the file storage code isn't tightly coupled to
posts, so it can be used to store any kind of file, not just images
belonging to posts.

app/models/media_asset.rb

@@ -38,7 +38,9 @@ class MediaAsset < ApplicationRecord
     end
 
     def open_file
-      storage_service.open(file_path)
+      file = storage_service.open(file_path)
+      frame_data = media_asset.pixiv_ugoira_frame_data&.data if media_asset.is_ugoira?
+      MediaFile.open(file, frame_data: frame_data)
     end
 
     def convert_file(media_file)

app/models/post.rb

@@ -74,36 +74,47 @@ class Post < ApplicationRecord
   module FileMethods
     extend ActiveSupport::Concern
 
-    def storage_manager
-      Danbooru.config.storage_manager
+    def seo_tags
+      presenter.humanized_essential_tag_string.gsub(/[^a-z0-9]+/, "_").gsub(/(?:^_+)|(?:_+$)/, "").gsub(/_{2,}/, "_")
     end
 
     def file(type = :original)
-      storage_manager.open_file(self, type)
+      media_asset.variant(type).open_file
     end
 
     def tagged_file_url(tagged_filenames: !CurrentUser.user.disable_tagged_filenames?)
-      storage_manager.file_url(self, :original, tagged_filenames: tagged_filenames)
+      slug = seo_tags if tagged_filenames
+      media_asset.variant(:original).file_url(slug)
     end
 
     def tagged_large_file_url(tagged_filenames: !CurrentUser.user.disable_tagged_filenames?)
-      storage_manager.file_url(self, :large, tagged_filenames: tagged_filenames)
+      slug = seo_tags if tagged_filenames
+
+      if media_asset.has_variant?(:sample)
+        media_asset.variant(:sample).file_url(slug)
+      else
+        media_asset.variant(:original).file_url(slug)
+      end
     end
 
     def file_url
-      storage_manager.file_url(self, :original)
+      media_asset.variant(:original).file_url
     end
 
     def large_file_url
-      storage_manager.file_url(self, :large)
+      if media_asset.has_variant?(:sample)
+        media_asset.variant(:sample).file_url
+      else
+        media_asset.variant(:original).file_url
+      end
     end
 
     def preview_file_url
-      storage_manager.file_url(self, :preview)
+      media_asset.variant(:preview).file_url
     end
 
     def crop_file_url
-      storage_manager.file_url(self, :crop)
+      media_asset.variant(:crop).file_url
     end
 
     def open_graph_image_url
@@ -1162,7 +1173,7 @@ class Post < ApplicationRecord
 
         ModAction.log("<@#{user.name}> regenerated IQDB for post ##{id}", :post_regenerate_iqdb, user)
       else
-        media_file = MediaFile.open(file, frame_data: pixiv_ugoira_frame_data&.data.to_a)
+        media_file = media_asset.variant(:original).open_file
         media_asset.distribute_files!(media_file)
 
         update!(