Fixes cover images for IDW's Transformers Humble Bundle epub: https://www.humblebundle.com/books/transformers-2019-idw-books

epub_cover_fixer.rb

# Fixes cover images in epub files
# Run this file wherever you want, just change the path in the last line to a directory containing all your epub files.

class EpubCoverFixer

  class MetaTagNotFound < StandardError; end

  attr_reader :starting_dir

  def initialize(dir)
    @starting_dir = dir
  end

  def run
    Dir.foreach(starting_dir) do |name|
      if name.match? /^\./
        puts "Skipping #{name}"
      else
        puts "#{name}"
        path = File.expand_path(starting_dir + '/' + name)
        unzipped_dir = unzip(path)
        update_cover(unzipped_dir)
        new_file = zip(unzipped_dir)
        cleanup(unzipped_dir)
      end
      puts "Fixed #{new_file}"
    end
  end

  private def unzip(path)
    puts "  Unzipping..."
    unzip_to = path.split('.').first
    `rm -rf #{unzip_to}`
    `unzip #{path} -d #{unzip_to}`
    unzip_to
  end

  private def update_cover(dir)
    puts "  Updating cover..."
    path = dir + '/OEBPS/content.opf'

    opf = File.read(path)
    if opf.match? /\<meta name="cover" content="cover-image" \/\>/
      opf.gsub!(/\<meta name="cover" content="cover-image" \/\>/, '<meta name="cover" content="cover-img" />')
      write_file(path, opf)
      puts "    Replaced <meta> tag"
    else
      raise MetaTagNotFound
    end
  end

  private def zip(dir)
    puts "  Zipping..."
    filename = "#{dir.split('/').last}-fixed.epub"
    `cd #{dir} && zip -r ../#{filename} *`
    "#{starting_dir}/#{filename}"
  end

  private def cleanup(dir)
    `rm -rf #{dir}`
  end

  private def write_file(path, contents)
    File.open(path, 'w') do |file|
      file.puts contents
    end
  end
end

EpubCoverFixer.new(File.join('/path', 'to', 'downloads')).run