Creating thumbnails for multi-page Pdfs in Carrierwave 2.2.3 and Rails 7

class VersionUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick
  include CarrierWave::RMagick
  storage :fog

  # @doc Specifies the position on remote hosting to save the file
  def store_dir = "shared/system/#{klass}/#{attachment}/#{id_partition}/#{style}/"

  # @doc Returns the model class name, camel_case and pluralized.
  # @example 
  #   irb(main):038:0> MyModel.first.file.file.klass
  #   => "my_models"
  def klass = model.class.name.underscore.pluralize

  # @doc Specifies the uploader's association name that is mounted on the model.  In the model `MyModel.rb`, we mount an uploader called VersionUploader, and we call that mount `file`.  This is considered the `attachment`
  # @example
  #   irb(main):039:0> MyModel.first.file.file.attachment
  #   => "files"
  def attachment = mounted_as.to_s.downcase.pluralize

  # @doc Creates a section of the final path partitioned by the id's of the model
  # @note
  #   These appear to be the id of the model, with a weird operation done to them.
  #   I sourced this code from the paperclip compatibility source code of Carrierwave's github as in my situation, I was converting from Paperclip to Carrierwave
  def id_partition = ("%09d" % model.id).scan(/.{3}/).join("/")

  # @doc Specifies the style of file for storage directory purposes
  def style = :original

  # @doc Returns the first page of a file
  version :thumb do
    process :to_array
    process :front
    process convert: "jpg"
    def full_filename(filename = model.file.filename) = "#{filename.split(".").first}.jpg"
    def style = :thumb
  end

  private

  # @doc Utilizes minimagick to split the uploading file from it's temporary path into an array
  # @note This code was sourced from https://github.com/janko/image_processing/wiki/Splitting-a-PDF-into-multiple-images, though I've made a few edits
  def to_array
    MiniMagick::Image.new(path).pages.count.times.map{ |page_number|
      ImageProcessing::MiniMagick
        .source(path)
        .convert("jpg")
        .colorspace("RGB")
        .loader(page: page_number).call
    }.first
  end

  # @doc Used in conjunction with `to_array` to return the first page of the array of pages
  # @note This utilizes the module CarrierWave::RMagick in some way...
  def front
    manipulate! do |frame, index|
      frame if index.zero?
    end
  end

end