Add support for editing for published statuses (#16697)

* Add support for editing for published statuses

* Fix references to stripped-out code

* Various fixes and improvements

* Further fixes and improvements

* Fix updates being potentially sent to unauthorized recipients

* Various fixes and improvements

* Fix wrong words in test

* Fix notifying accounts that were tagged but were not in the audience

* Fix mistake

app/lib/activitypub/parser/media_attachment_parser.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+class ActivityPub::Parser::MediaAttachmentParser
+  include JsonLdHelper
+
+  def initialize(json)
+    @json = json
+  end
+
+  # @param [MediaAttachment] previous_record
+  def significantly_changes?(previous_record)
+    remote_url != previous_record.remote_url ||
+      thumbnail_remote_url != previous_record.thumbnail_remote_url ||
+      description != previous_record.description
+  end
+
+  def remote_url
+    Addressable::URI.parse(@json['url'])&.normalize&.to_s
+  rescue Addressable::URI::InvalidURIError
+    nil
+  end
+
+  def thumbnail_remote_url
+    Addressable::URI.parse(@json['icon'].is_a?(Hash) ? @json['icon']['url'] : @json['icon'])&.normalize&.to_s
+  rescue Addressable::URI::InvalidURIError
+    nil
+  end
+
+  def description
+    @json['summary'].presence || @json['name'].presence
+  end
+
+  def focus
+    @json['focalPoint']
+  end
+
+  def blurhash
+    supported_blurhash? ? @json['blurhash'] : nil
+  end
+
+  def file_content_type
+    @json['mediaType']
+  end
+
+  private
+
+  def supported_blurhash?
+    components = begin
+      blurhash = @json['blurhash']
+
+      if blurhash.present? && /^[\w#$%*+-.:;=?@\[\]^{|}~]+$/.match?(blurhash)
+        Blurhash.components(blurhash)
+      end
+    end
+
+    components.present? && components.none? { |comp| comp > 5 }
+  end
+end