# A class for retrieving metadata on a particular image.
# See the Djatoka documentation on the {getMetadata service}[http://sourceforge.net/apps/mediawiki/djatoka/index.php?title=Djatoka_OpenURL_Services#info:lanl-repo.2Fsvc.2FgetMetadata]
class Djatoka::Metadata
  attr_accessor :rft_id, :identifier, :imagefile, :width, :height, :dwt_levels,
    :levels, :layer_count, :response, :resolver
  include Djatoka::Net

  def initialize(resolver, rft_id)
    @resolver = resolver
    @rft_id = rft_id
  end

  # To actually retrieve metadata from the server this method must be called.
  def perform
    @response = get_json(url)
    if @response
      @identifier = response['identifier']
      @imagefile = response['imagefile']
      @width = response['width']
      @height = response['height']
      @dwt_levels = response['dwtLevels']
      @levels = response['levels']
      @layer_count = response['compositingLayerCount']
    end
    self
  end

  # If #perform has been called then this can tell you whether
  # the status of the request was 'OK' or not (nil).
  def status
    if @response
      'OK'
    else
      nil
    end
  end

  # Returns an Addressable::URI which can be used to retrieve metadata from the
  # image server, inspected for query_values, or changed before a request.
  def uri
    uri = Addressable::URI.new(resolver.base_uri_params)
    uri.query_values = {'url_ver'=>'Z39.88-2004','svc_id'=>'info:lanl-repo/svc/getMetadata',
    'rft_id'=>rft_id }
    uri
  end

  # Returns a URL as a String for retrieving metdata from the image server.
  def url
    uri.to_s
  end

  # The Djatoka image server {determines level logic}[http://sourceforge.net/apps/mediawiki/djatoka/index.php?title=Djatoka_Level_Logic]
  # different from the number of dwtLevels. This method determines the height and
  # width of each level. Djatoka only responds with the largest level, so we have
  # to determine these other levels ourself.
  def all_levels
    perform if !response # if we haven't already performed the metadata query do it now
    levels_hash = Hashie::Mash.new
    dwt_levels_i = dwt_levels.to_i
    (0..dwt_levels_i).each do |level_num|
      level_height = height.to_i
      level_width = width.to_i

      times_to_halve = dwt_levels_i - level_num
      times_to_halve.times do
        level_height = level_height / 2
        level_width = level_width / 2
      end

      levels_hash[level_num] = {:height => level_height, :width => level_width}
    end
    levels_hash
  end

end