factor out a bunch of file types

app/models/attachment.rb

@@ -15,12 +15,25 @@ class Attachment < ApplicationRecord
                       end
                     }
 
-  validates_attachment_content_type :file, content_type: [
+  validates_attachment_content_type :file, content_type: Attachable.allowed_types
-    %r{\Aimage/.*\Z},
-    %r{\Avideo/.*\Z}
-  ]
 
   def image?
-    file.instance.file_content_type =~ /image/
+    file.instance.file_content_type =~ %r{\Aimage}
+  end
+
+  def audio?
+    file.instance.file_content_type ~= %r{\Aaudio}
+  end
+
+  def text?
+    file.instance.file_content_type ~= %r{\Atext}
+  end
+
+  def pdf?
+    file.instance.file_content_type == 'application/pdf'
+  end
+
+  def document?
+    text? || pdf?
   end
 end

app/models/concerns/attachable.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+module Attachable
+  extend ActiveSupport::Concern
+
+  has_many :attachments, as: :attachable, dependent: :destroy
+
+  def images
+    attachments.where(file_content_type: self.image_types)
+  end
+
+  def audios
+    attachments.where(file_content_type: self.audio_types)
+  end
+
+  def texts
+    attachments.where(file_content_type: self.text_types)
+  end
+
+  def pdfs
+    attachments.where(file_content_type: self.pdf_types)
+  end
+
+  def documents
+    attachments.where(file_content_type: self.text_types + self.pdf_types)
+  end
+
+  class << self
+    def image_types
+      ['image/png', 'image/gif', 'image/jpeg']
+    end
+
+    def audio_types
+      ['audio/ogg', 'audio/mp3']
+    end
+
+    def text_types
+      ['text/plain', 'text/markdown']
+    end
+
+    def pdf_types
+      ['application/pdf']
+    end
+
+    def allowed_types
+      image_types + audio_types + text_types + pdf_types
+    end
+  end
+end

app/models/topic.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 class Topic < ApplicationRecord
   include TopicsHelper
+  include Attachable
 
   belongs_to :user
   belongs_to :defer_to_map, class_name: 'Map', foreign_key: 'defer_to_map_id'
@@ -21,8 +22,6 @@ class Topic < ApplicationRecord
   validates :permission, presence: true
   validates :permission, inclusion: { in: Perm::ISSIONS.map(&:to_s) }
 
-  has_many :attachments, as: :attachable, dependent: :destroy
-
   def synapses
     synapses1.or(synapses2)
   end