item_fetcher_worker.rb

class ItemFetcherWorker < BackgrounDRb::MetaWorker
  set_worker_name :item_fetcher_worker
  def create(args = nil)
  end

  def set_search(search)
    @search = search
  end

  def fetch_query_and_items
    times_tried = 0
    begin
      times_tried = times_tried + 1
      @search.do!
    rescue
      times_tried < 4 ? retry : raise
    end
    fetch_items
  end

  def fetch_items
    times_tried = 0
    begin
      times_tried = times_tried + 1
      @search.items
    rescue
      times_tried < 4 ? retry : raise
    end
  end

  def fetch_next_page_of_items(params = {})
    # query_options = params[:query_options]
    total_pages = params[:total_pages].to_i || 1
    current_page = params[:current_page].to_i || 1
    depth = params[:depth] || 2

    if current_page < total_pages
      new_params  = @search.request.call_params.merge({:page_number => (current_page.to_i + 1).to_s})

      logger.info("---------------------------------\nSearch begun for:\n #{@search.request.call_params}\nwith new parameters:\n #{new_params}")
      @search = Search.new(new_params)
      @search.do!
      @search.items
      logger.info("Search finished!\n---------------------------------\n")

      fetch_next_page_of_items(:total_pages => total_pages, :current_page => current_page, :depth => depth-1) if depth > 0
    end
  rescue
    logger.error("Search finished but something broke:\n #{$!}\n---------------------------------\n")
  end
end

search.rb

class Search
  # Example: Search.new(:query_keywords => 'canon (450d, xti)', :"price_min.Value" => 400, :"price_max.Value" => 1100, :max_entries => 5)
  #
  # Also perfmorms the EbayShopping::Request.
  #
  # Raises hell of exceptions some of which are:
  #   SocketError (getaddrinfo: nodename nor servname provided, or not known)
  #   EbayShopping::TimeoutError
  attr_reader :request
  def initialize(params)
    params_default = {
      :max_entries  => '5', 
      :include_selector =>'Details,SellerInfo',
      :item_type => 'AllItemTypes', # includes "Store Inventory format" in addiction to auction items
      :items_available_to => 'GR', 
      :item_sort => 'EndTime', # Maybe by best-match?
      :payment_method => 'PayPal'
      #:site_id => '3' # Ebay.co.uk
    }
    @request = EbayShopping::Request.new :find_items_advanced, params_default.merge(params)
    @error = nil
  end

  def cached?
    if @request.has_cached_response?
      self.do!
      true
    end
  end

  def do!
    @response = @request.response
  end

  # Returns an array of Items with the result set from the request/response.
  def items(options = {})
    return nil if total_items == 0

    options = {:caclulate_shipping => true, :shipping_for_country_code => 'GR', :get_seller_details => false}.merge(options)    
    @items = @response.items.map{ |item| EbayItem.find_or_create_from_ebay_response(item, options) }
  end

  def total_items
    @total_items ||= @response.total_items
  end

  def items_cached?
    return true unless @response.items # Return true if items is empty
    return EbayItem.count(:conditions => {:item_id => @response.items.map { |item| item.item_id } }) == @response.items.size
  end
end

search_controller.rb

class SearchController < ApplicationController
  layout 'default'

  # GET /
  # GET /search
  # GET /search/index
  def index; @pagetitle = 'simpleBay: Τί ψάχνεις σήμερα;'; end

  # GET /search?q=''&max_price=''&...
  # GET /search/search?q=''&max_price=''&...
  #
  # Required parameters: q
  # Optional parameters: page, min_price, max_price, max_entries
  def search
    @repeat_request = false

    if params[:q].nil? or (@q = params[:q]).empty?
      render :text => 'Καλό θα ήταν να εισάγετε κάτι για αναζήτηση :)' and return
    end

    @pagetitle = "simpleBay: Αναζήτση για #{@q}"
    parse_ebay_parameters
    search = Search.new(@ebay_req_params)

    fetcher = MiddleMan.worker(:item_fetcher_worker)
    fetcher.set_search(:arg => search)

    if search.cached?
      @total_results = search.total_items
      if search.items_cached?
        @items = search.items
        @current_page, @total_pages = (@ebay_req_params[:page_number] || 1).to_i, (@total_results / @ebay_req_params[:max_entries].to_f).ceil
        if @total_results > (@current_page * @ebay_req_params[:max_entries].to_i)
          fetcher.async_fetch_next_page_of_items(:arg => {:current_page => @current_page, :total_pages => @total_pages})
        end
      else # if items are NOT cached.
        @repeat_request = true
        fetcher.async_fetch_items unless request.xhr?
      end
    else # if search is NOT cached.
      @repeat_request = true
      fetcher.async_fetch_query_and_items unless request.xhr?
    end

    # Setup params for periodically_call_remote in search view template if request is to be repeated.
    @ajax_url_params = {:action => :search,
                        :q => @q,
                        :page => @ebay_req_params[:page_number],
                        :min_price => @min_price,
                        :max_price => @max_price,
                        :max_entries => @max_entries } if @repeat_request

  rescue  EbayShopping::TimeoutError
    render :text => 'Ebay timeout error, please try again later'
  end

  protected
  def parse_ebay_parameters
    @ebay_req_params = { :query_keywords => @q }

    @ebay_req_params[:page_number] = params[:page] || '1'

    if @min_price = params[:min_price] and !@min_price.empty?
      @ebay_req_params[:"price_min.Value"] = EbayShopping::Money.euros_to_dollars(@min_price)
    end

    if @max_price = params[:max_price] and !@max_price.empty?
      @ebay_req_params[:"price_max.Value"] = EbayShopping::Money.euros_to_dollars(@max_price)
    end

    @ebay_req_params[:max_entries] = @max_entries = params[:max_entries] ? params[:max_entries] : 10
  end
end