Skip books that don't support PDF

src/fetch.cr

@@ -25,6 +25,7 @@ module Muse::Dl
         return
       end
 
+      # TODO: Remove this hardcoding, and make this more generic by generating it within the Book class
       url = "https://muse.jhu.edu/chapter/#{chapter_id}/pdf"
       headers = HEADERS.merge({
         "Referer" => "https://muse.jhu.edu/verify?url=%2Fchapter%2F#{chapter_id}%2Fpdf",

src/muse-dl.cr

@@ -15,6 +15,10 @@ module Muse::Dl
       return unless thing
 
       if thing.is_a? Muse::Dl::Book
+        unless thing.formats.includes? :pdf
+          STDERR.puts "Book not available in PDF format, skipping: #{url}"
+          return
+        end
         # Will have no effect if parser has a custom title
         parser.output = Util.slug_filename "#{thing.title}.pdf"