#--
# Copyright (c) 2006 Herryanto Siatono, Pluit Solutions
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#++

require 'net/http'
require 'hpricot'
require 'cgi'
require 'openssl'
require 'uri'
require 'digest/sha2'
require 'base64'

module Amazon
  class RequestError < StandardError; end
  
  class Ecs
    SERVICE_URLS = {:us => 'http://webservices.amazon.com/onca/xml',
        :uk => 'http://webservices.amazon.co.uk/onca/xml',
        :ca => 'http://webservices.amazon.ca/onca/xml',
        :de => 'http://webservices.amazon.de/onca/xml',
        :jp => 'http://webservices.amazon.co.jp/onca/xml',
        :fr => 'http://webservices.amazon.fr/onca/xml'
    }
    
    @@options = {}
    @@debug = false

    # Default search options
    def self.options
      @@options
    end
    
    # Set default search options
    def self.options=(opts)
      @@options = opts
    end
    
    # Get debug flag.
    def self.debug
      @@debug
    end
    
    # Set debug flag to true or false.
    def self.debug=(dbg)
      @@debug = dbg
    end
    
    def self.configure(&proc)
      raise ArgumentError, "Block is required." unless block_given?
      yield @@options
    end
    
    # Search amazon items with search terms. Default search index option is 'Books'.
    # For other search type other than keywords, please specify :type => [search type param name].
    def self.item_search(terms, opts = {})
      opts[:operation] = 'ItemSearch'
      opts[:search_index] = opts[:search_index] || 'Books'
      
      type = opts.delete(:type)
      if type 
        opts[type.to_sym] = terms
      else 
        opts[:keywords] = terms
      end
      
      self.send_request(opts)
    end

    # Search an item by ASIN no.
    def self.item_lookup(item_id, opts = {})
      opts[:operation] = 'ItemLookup'
      opts[:item_id] = item_id
      
      self.send_request(opts)
    end    
          
    # Generic send request to ECS REST service. You have to specify the :operation parameter.
    def self.send_request(opts)
      opts = self.options.merge(opts) if self.options
      request_url = prepare_url(opts)
      log "Request URL: #{request_url}"
      
      res = Net::HTTP.get_response(URI::parse(request_url))
      unless res.kind_of? Net::HTTPSuccess
        raise Amazon::RequestError, "HTTP Response: #{res.code} #{res.message}"
      end
      Response.new(res.body)
    end

    # Response object returned after a REST call to Amazon service.
    class Response
      # XML input is in string format
      def initialize(xml)
        @doc = Hpricot(xml)
      end

      # Return Hpricot object.
      def doc
        @doc
      end

      # Return true if request is valid.
      def is_valid_request?
        (@doc/"isvalid").inner_html == "True"
      end

      # Return true if response has an error.
      def has_error?
        !(error.nil? || error.empty?)
      end

      # Return error message.
      def error
        Element.get(@doc, "error/message")
      end
      
      # Return error code
      def error_code
        Element.get(@doc, "error/code")
      end
      
      # Return an array of Amazon::Element item objects.
      def items
        unless @items
          @items = (@doc/"item").collect {|item| Element.new(item)}
        end
        @items
      end
      
      # Return the first item (Amazon::Element)
      def first_item
        items.first
      end
      
      # Return current page no if :item_page option is when initiating the request.
      def item_page
        unless @item_page
          @item_page = (@doc/"itemsearchrequest/itempage").inner_html.to_i
        end
        @item_page
      end

      # Return total results.
      def total_results
        unless @total_results
          @total_results = (@doc/"totalresults").inner_html.to_i
        end
        @total_results
      end
      
      # Return total pages.
      def total_pages
        unless @total_pages
          @total_pages = (@doc/"totalpages").inner_html.to_i
        end
        @total_pages
      end
    end
    
    protected
      def self.log(s)
        return unless self.debug
        if defined? RAILS_DEFAULT_LOGGER
          RAILS_DEFAULT_LOGGER.error(s)
        elsif defined? LOGGER
          LOGGER.error(s)
        else
          puts s
        end
      end
      
    private 
    def self.prepare_url(opts)
      country = opts.delete(:country)
      country = (country.nil?) ? 'us' : country
      request_url = SERVICE_URLS[country.to_sym]
      raise Amazon::RequestError, "Invalid country '#{country}'" unless request_url
      secret_access_key = opts.delete(:secret_access_key)
      raise Amazon::RequestError, "secret_access_key is nil" unless secret_access_key
      opts[:Timestamp] = DateTime.now.new_offset.strftime('%Y-%m-%dT%XZ')
      opts[:Service] = "AWSECommerceService"
      opts[:Version] = "2009-01-06"
      qs = opts.map do |k, v|
        [camelize(k.to_s), v]
      end
      qs.reject! do |k,v| v.to_s.empty? end
      qs.sort!
      qs.map! do |k,v|
        v = v.join(',') if v.is_a? Array
        [k, CGI.escape(v.to_s)] * "="
      end
      qs = qs * "&"
      uri = URI.parse(request_url + "?" + qs)
      msg = [ 'GET', uri.host, uri.path, uri.query ].join("\n")
      dig = hmac_sha256(secret_access_key, msg)
      sig = CGI.escape(Base64.encode64(dig).chomp)
      "#{request_url}?#{qs}&Signature=#{sig}"
    end

    IPAD = "\x36"
    OPAD = "\x5c"
    def self.hmac_sha256(key, message)
      ikey = IPAD * 64
      okey = OPAD * 64
      key.size.times do |i|
        ikey[i] = key[i] ^ ikey[i]
        okey[i] = key[i] ^ okey[i]
      end
      value = Digest::SHA256.digest(ikey + message)
      value = Digest::SHA256.digest(okey + value)
    end

    def self.camelize(s)
      s.to_s.gsub(/\/(.?)/) { "::" + $1.upcase }.gsub(/(^|_)(.)/) { $2.upcase }
    end
  end

  # Internal wrapper class to provide convenient method to access Hpricot element value.
  class Element
    # Pass Hpricot::Elements object
    def initialize(element)
      @element = element
    end

    # Returns Hpricot::Elments object    
    def elem
      @element
    end
    
    # Find Hpricot::Elements matching the given path. Example: element/"author".
    def /(path)
      elements = @element/path
      return nil if elements.size == 0
      elements
    end
    
    # Find Hpricot::Elements matching the given path, and convert to Amazon::Element.
    # Returns an array Amazon::Elements if more than Hpricot::Elements size is greater than 1.
    def search_and_convert(path)
      elements = self./(path)
      return unless elements
      elements = elements.map{|element| Element.new(element)}
      return elements.first if elements.size == 1
      elements
    end

    # Get the text value of the given path, leave empty to retrieve current element value.
    def get(path='')
      Element.get(@element, path)
    end
    
    # Get the unescaped HTML text of the given path.
    def get_unescaped(path='')
      Element.get_unescaped(@element, path)
    end
    
    # Get the array values of the given path.
    def get_array(path='')
      Element.get_array(@element, path)
    end

    # Get the children element text values in hash format with the element names as the hash keys.
    def get_hash(path='')
      Element.get_hash(@element, path)
    end

    # Similar to #get, except an element object must be passed-in.
    def self.get(element, path='')
      return unless element
      result = element.at(path)
      result = result.inner_html if result
      result
    end
    
    # Similar to #get_unescaped, except an element object must be passed-in.    
    def self.get_unescaped(element, path='')
      result = get(element, path)
      CGI::unescapeHTML(result) if result
    end

    # Similar to #get_array, except an element object must be passed-in.
    def self.get_array(element, path='')
      return unless element
      
      result = element/path
      if (result.is_a? Hpricot::Elements) || (result.is_a? Array)
        parsed_result = []
        result.each {|item|
          parsed_result << Element.get(item)
        }
        parsed_result
      else
        [Element.get(result)]
      end
    end

    # Similar to #get_hash, except an element object must be passed-in.
    def self.get_hash(element, path='')
      return unless element
    
      result = element.at(path)
      if result
        hash = {}
        result = result.children
        result.each do |item|
          hash[item.name.to_sym] = item.inner_html
        end 
        hash
      end
    end
    
    def to_s
      elem.to_s if elem
    end
  end
end