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, expected_update_period_in_days, and extract are required") unless options[:expected_update_period_in_days].present? && options[:url].present? && options[:extract].present?
    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)
        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

        previous_payloads = events.order("id desc").limit(UNIQUENESS_LOOK_BACK).pluck(:payload).map(&:to_json) if options[:mode].to_s == "on_change"
        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 !options[:mode] || options[:mode].to_s == "all" || (options[:mode].to_s == "on_change" && !previous_payloads.include?(result.to_json))
            log "Storing new result for '#{name}': #{result.inspect}"
            create_event :payload => result
          end
        end
      end
      hydra.queue request
      hydra.run
    end

    private

    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