module RailsConnector
  # Provides an enumerator, to iterate over obj search results and return "real" objs.
  # This is done using the {http://ruby-doc.org/core-1.8.7/Enumerable.html <code>Enumerable</code> mixin}, which provided methods like <code>map</code>, <code>select</code> or <code>take</code>.
  #
  # This enumerator is lazy. Let's say, that when looking for Objs with the ObjClass Publication there are 123 objs in total. Now <code>enum.take(10)</code> will only fetch the first 10 objs, leaving the other 113 objs untouched.
  # This also means, that iterating multiple times over this enumerator, each time the search results and objs are fetched again. If you want to get all objs at once, use <code>enum.to_a</code>.
  #
  # For all possible <code>query</code>'s and <code>options</code> have a look at the cms api documentation about objs/search.
  # There is one exception: To adjust how many search results should be fetch with one chunk, use the option <code>:batch_size</code>. The default is <code>10</code>. The <code>:size</code> option will be silently ignored.
  #
  # @example All objs, which are Publications
  #   enum = ObjSearchEnumerator([{:field => '_obj_class', :operator => 'equal', :value => 'Publication'}])
  #   enum.each { |obj| puts obj.path }
  class ObjSearchEnumerator
    include Enumerable

    attr_reader :query
    attr_reader :options

    # @param [Array] query
    # @param [Hash] options
    def initialize(query, options = {})
      @query = query
      @query.freeze

      options.delete(:size)
      options.delete('size')
      if batch_size = options.delete(:batch_size)
        options[:size] = batch_size
      end
      @options = options
      @options.freeze
    end

    def each
      offset = 0
      current_batch, total = fetch_next_batch(offset)
      loop do
        if current_batch.size == 0
          if offset < total
            current_batch, total = fetch_next_batch(offset)
          else
            raise StopIteration
          end
        end

        offset += 1
        hit = current_batch.shift
        yield Obj.find(hit['id'])
      end
    end

    # The total size of all results.
    # @return [Integer]
    def size
      if @size.blank?
        @size = CmsRestApi.get(resource_path, {:query => query, :size => 1})['total'].to_i
      end
      @size
    end

    alias_method :length, :size

    private

    def fetch_next_batch(offset)
      request_result = CmsRestApi.get(resource_path, search_dsl(offset))

      [request_result['results'], request_result['total'].to_i]
    end

    def resource_path
      "revisions/#{Workspace.current.revision_id}/objs/search"
    end

    def search_dsl(offset)
      options.merge({
        :offset => offset,
        :query => query,
      })
    end
  end
end