require 'action_controller'

module FileBlobs

# Module mixed into ActionController::DataStreaming.
module ActionControllerDataStreamingExtensions
  ETAG = 'ETag'.freeze
  HTTP_IF_NONE_MATCH = 'HTTP_IF_NONE_MATCH'.freeze

  # Sends a file blob to the browser.
  #
  # This method uses HTTP's strong etag feature to facilitate serving the files
  # from a cache whenever possible.
  #
  # @param [FileBlobs::FileBlobProxy] proxy a proxy for a collection of
  #     attributes generated by has_file_blob
  # @param [Hash<Symbol, Object>] options tweaks the options passed to the
  #     underlying send_data call; this method sets the  :filename and :type
  #     options, but their values can be overridden by the options hash
  # @see ActionController::DataStreaming#send_data
  def send_file_blob(proxy, options = {})
    if request.get_header(HTTP_IF_NONE_MATCH) == proxy.blob_id
      head :not_modified
    else
      response.headers[ETAG] = proxy.blob_id
      send_options = { type: proxy.mime_type, filename: proxy.original_name }
      send_options.merge! options
      send_data proxy.data, send_options
    end
  end

  # Creates the table used to hold file blobs.
  #
  # @param [Symbol] table_name the name of the table used to hold file data
  # @param [Hash<Symbol, Object>] options
  # @option options [Boolean] null true
  # @option options [Integer] blob_limit the maximum file size that can be
  #     stored in the table; defaults to 1 megabyte
  def file_blob(column_name_base = :file, options = {}, &block)
    allow_null = options[:null] || false
    mime_type_limit = options[:mime_type_limit] || 64
    file_name_limit = options[:file_name_limit] || 256

    # The index is needed for garbage-collection eligibility checks.
    string :"#{column_name_base}_blob_id", limit: 48, null: allow_null,
           index: true

    integer :"#{column_name_base}_size", null: allow_null
    string :"#{column_name_base}_mime_type", limit: mime_type_limit,
           null: allow_null
    string :"#{column_name_base}_original_name", limit: file_name_limit,
           null: allow_null
  end
end  # module FileBlobs::ActionControllerDataStreamingExtensions

end  # namespace FileBlobs

ActionController::DataStreaming.class_eval do
  include FileBlobs::ActionControllerDataStreamingExtensions
end