Add blurhash to preview cards (#13984)

Fixes #13001

app/models/preview_card.rb

@@ -23,19 +23,25 @@
 #  updated_at                   :datetime         not null
 #  embed_url                    :string           default(""), not null
 #  image_storage_schema_version :integer
+#  blurhash                     :string
 #
 
 class PreviewCard < ApplicationRecord
   IMAGE_MIME_TYPES = ['image/jpeg', 'image/png', 'image/gif'].freeze
   LIMIT = 1.megabytes
 
+  BLURHASH_OPTIONS = {
+    x_comp: 4,
+    y_comp: 4,
+  }.freeze
+
   self.inheritance_column = false
 
   enum type: [:link, :photo, :video, :rich]
 
   has_and_belongs_to_many :statuses
 
-  has_attached_file :image, styles: ->(f) { image_styles(f) }, convert_options: { all: '-quality 80 -strip' }
+  has_attached_file :image, processors: [:thumbnail, :blurhash_transcoder], styles: ->(f) { image_styles(f) }, convert_options: { all: '-quality 80 -strip' }
 
   include Attachmentable
 
@@ -72,6 +78,7 @@ class PreviewCard < ApplicationRecord
           geometry: '400x400>',
           file_geometry_parser: FastGeometryParser,
           convert_options: '-coalesce -strip',
+          blurhash: BLURHASH_OPTIONS,
         },
       }