Retrospring/app/uploaders/profile_header_uploader.rb

class ProfileHeaderUploader < CarrierWave::Uploader::Base
  include CarrierWave::Compatibility::Paperclip
  include CarrierWave::MiniMagick

  # Choose what kind of storage to use for this uploader:
  storage :fog

  # Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
    "/uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  def paperclip_path
    "users/:attachment/:id_partition/:style/:basename.:extension"
  end

  # Provide a default URL as a default if there hasn't been a file uploaded:
  def default_url(*args)
    # For Rails 3.1+ asset pipeline compatibility:
    # ActionController::Base.helpers.asset_path("fallback/" + [version_name, "default.png"].compact.join('_'))

    "/images/header/" + [version_name, "no_header.jpg"].compact.join('/')
  end

  version :web do
    process resize_to_fit: [1500, 350]
  end
  version :mobile do
    process resize_to_fit: [450, 105]
  end
  version :retina do
    process resize_to_fit: [900, 210]
  end

  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
  # def extension_whitelist
  #   %w(jpg jpeg gif png)
  # end

  # Override the filename of the uploaded files:
  # Avoid using model.id or version_name here, see uploader/store.rb for details.
  # def filename
  #   "something.jpg" if original_filename
  # end
end