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Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/models/concerns/coverable.rb

@@ -0,0 +1,50 @@
+module Coverable
+  extend ActiveSupport::Concern
+
+  COVER_IMAGE_TYPES = %w[image/png image/jpeg image/webp].freeze
+  MAX_COVER_BYTES = 5.megabytes
+
+  included do
+    has_one_attached :cover_image
+    has_one_attached :cover_slate
+
+    validate :cover_image_file_type, if: -> { cover_image.attached? && cover_image.blob&.new_record? }
+    validate :cover_image_file_size, if: -> { cover_image.attached? && cover_image.blob&.new_record? }
+  end
+
+  def cover_image_attached?
+    cover_image.attached?
+  end
+
+  def cover_url
+    return unless cover_image.attached?
+
+    Rails.application.routes.url_helpers.rails_blob_path(cover_image, only_path: true)
+  end
+
+  def effective_cover_url
+    if cover_image.attached?
+      cover_url
+    else
+      cover_parent&.effective_cover_url
+    end
+  end
+
+  private
+
+  def cover_parent
+    nil
+  end
+
+  def cover_image_file_type
+    return if cover_image.content_type.in?(COVER_IMAGE_TYPES)
+
+    errors.add(:cover_image, I18n.t("coverable.errors.invalid_type"))
+  end
+
+  def cover_image_file_size
+    return if cover_image.byte_size <= MAX_COVER_BYTES
+
+    errors.add(:cover_image, I18n.t("coverable.errors.too_large"))
+  end
+end