require 'nokogiri'
require 'typhoeus'
require 'date'

module Agents
  class WebsiteAgent < Agent
    cannot_receive_events!

    description <<-MD
      The WebsiteAgent scrapes a website, XML document, or JSON feed and creates Events based on the results.

      Specify a `url` and select a `mode` for when to create Events based on the scraped data, either `all` or `on_change`.

      The `type` value can be `xml`, `html`, or `json`.

      To tell the Agent how to parse the content, specify `extract` as a hash with keys naming the extractions and values of hashes.

      When parsing HTML or XML, these sub-hashes specify how to extract with a `:css` CSS selector and either `:text => true` or `attr` pointing to an attribute name to grab.  An example:

          :extract => {
            :url => { :css => "#comic img", :attr => "src" },
            :title => { :css => "#comic img", :attr => "title" },
            :body_text => { :css => "div.main", :text => true }
          }

      When parsing JSON, these sub-hashes specify [JSONPaths](http://goessner.net/articles/JsonPath/) to the values that you care about.  For example:

          :extract => {
            :title => { :path => "results.data[*].title" },
            :description => { :path => "results.data[*].description" }
          }

      Note that for all of the formats, whatever you extract MUST have the same number of matches for each extractor.  E.g., if you're extracting rows, all extractors must match all rows.  For generating CSS selectors, something like [SelectorGadget](http://selectorgadget.com) may be helpful.

      Set `expected_update_period_in_days` to the maximum amount of time that you'd expect to pass between Events being created by this Agent.
    MD

    event_description do
      "Events will have the fields you specified.  Your options look like:\n\n    #{Utils.pretty_print options[:extract]}"
    end

    default_schedule "every_12h"

    UNIQUENESS_LOOK_BACK = 30

    def working?
      event_created_within(options[:expected_update_period_in_days]) && !recent_error_logs?
    end

    def default_options
      {
          :expected_update_period_in_days => "2",
          :url => "http://xkcd.com",
          :type => "html",
          :mode => :on_change,
          :extract => {
              :url => {:css => "#comic img", :attr => "src"},
              :title => {:css => "#comic img", :attr => "title"}
          }
      }
    end

    def validate_options
      errors.add(:base, "url and expected_update_period_in_days are required") unless options[:expected_update_period_in_days].present? && options[:url].present?
      if !options[:extract].present? && extraction_type != "json"
        errors.add(:base, "extract is required for all types except json")
      end
    end

    def check
      hydra = Typhoeus::Hydra.new
      log "Fetching #{options[:url]}"
      request = Typhoeus::Request.new(options[:url], :followlocation => true)
      request.on_failure do |response|
        error "Failed: #{response.inspect}"
      end
      request.on_success do |response|
        doc = parse(response.body)

        if extract_full_json?
          result = doc
          if store_payload? result
            log "Storing new result for '#{name}': #{result.inspect}"
            create_event :payload => result
          end
        else
          output = {}
          options[:extract].each do |name, extraction_details|
            result = if extraction_type == "json"
                       output[name] = Utils.values_at(doc, extraction_details[:path])
                     else
                       output[name] = doc.css(extraction_details[:css]).map { |node|
                         if extraction_details[:attr]
                           node.attr(extraction_details[:attr])
                         elsif extraction_details[:text]
                           node.text()
                         else
                           error ":attr or :text is required on HTML or XML extraction patterns"
                           return
                         end
                       }
                     end
            log "Extracting #{extraction_type} at #{extraction_details[:path] || extraction_details[:css]}: #{result}"
          end

          num_unique_lengths = options[:extract].keys.map { |name| output[name].length }.uniq

          if num_unique_lengths.length != 1
            error "Got an uneven number of matches for #{options[:name]}: #{options[:extract].inspect}"
            return
          end
      
          num_unique_lengths.first.times do |index|
            result = {}
            options[:extract].keys.each do |name|
              result[name] = output[name][index]
              if name.to_s == 'url'
                result[name] = URI.join(options[:url], result[name]).to_s if (result[name] =~ URI::DEFAULT_PARSER.regexp[:ABS_URI]).nil?
              end
            end

            if store_payload? result
              log "Storing new parsed result for '#{name}': #{result.inspect}"
              create_event :payload => result
            end
          end
        end
      end
      hydra.queue request
      hydra.run
    end

    private

    def store_payload? result
      !options[:mode] || options[:mode].to_s == "all" || (options[:mode].to_s == "on_change" && !previous_payloads.include?(result.to_json))
    end

    def previous_payloads
      events.order("id desc").limit(UNIQUENESS_LOOK_BACK).pluck(:payload).map(&:to_json) if options[:mode].to_s == "on_change"
    end

    def extract_full_json?
      (!options[:extract].present? && extraction_type == "json")
    end

    def extraction_type
      (options[:type] || begin
        if options[:url] =~ /\.(rss|xml)$/i
          "xml"
        elsif options[:url] =~ /\.json$/i
          "json"
        else
          "html"
        end
      end).to_s
    end

    def parse(data)
      case extraction_type
        when "xml"
          Nokogiri::XML(data)
        when "json"
          JSON.parse(data)
        when "html"
          Nokogiri::HTML(data)
        else
          raise "Unknown extraction type #{extraction_type}"
      end
    end
  end
end