# frozen_string_literal: true

module Html2rss
  ##
  # Provides a namespace for item extractors.
  module ItemExtractors
    ##
    # The Error class to be thrown when an unknown extractor name is requested.
    class UnknownExtractorName < Html2rss::Error; end

    ##
    # Maps the extractor name to the class implementing the extractor.
    #
    # The key is the name to use in the feed config.
    NAME_TO_CLASS = {
      attribute: Attribute,
      href: Href,
      html: Html,
      static: Static,
      text: Text
    }.freeze

    ##
    # Maps the extractor class to its corresponding options class.
    ITEM_OPTION_CLASSES = Hash.new do |hash, klass|
      hash[klass] = klass.const_get(:Options)
    end

    DEFAULT_EXTRACTOR = :text

    ##
    # Retrieves an element from Nokogiri XML based on the selector.
    #
    # @param xml [Nokogiri::XML::Document]
    # @param selector [String, nil]
    # @return [Nokogiri::XML::ElementSet] selected XML elements
    def self.element(xml, selector)
      selector ? xml.css(selector) : xml
    end

    ##
    # Creates an instance of the requested item extractor.
    #
    # @param attribute_options [Hash<Symbol, Object>]
    #   Should contain at least `:extractor` (the name) and required options for that extractor.
    # @param xml [Nokogiri::XML::Document]
    # @return [Object] instance of the specified item extractor class
    def self.item_extractor_factory(attribute_options, xml)
      extractor_name = attribute_options[:extractor]&.to_sym || DEFAULT_EXTRACTOR
      extractor_class = find_extractor_class(extractor_name)
      options_instance = build_options_instance(extractor_class, attribute_options)
      create_extractor_instance(extractor_class, xml, options_instance)
    end

    ##
    # Finds the extractor class based on the name.
    #
    # @param extractor_name [Symbol] the name of the extractor
    # @return [Class] the class implementing the extractor
    # @raise [UnknownExtractorName] if the extractor class is not found
    def self.find_extractor_class(extractor_name)
      NAME_TO_CLASS[extractor_name] || raise(UnknownExtractorName,
                                             "Unknown extractor name '#{extractor_name}' requested in NAME_TO_CLASS")
    end

    ##
    # Builds the options instance for the extractor class.
    #
    # @param extractor_class [Class] the class implementing the extractor
    # @param attribute_options [Hash<Symbol, Object>] the attribute options
    # @return [Object] an instance of the options class for the extractor
    def self.build_options_instance(extractor_class, attribute_options)
      options = attribute_options.slice(*extractor_class::Options.members)
      ITEM_OPTION_CLASSES[extractor_class].new(options)
    end

    ##
    # Creates an instance of the extractor class.
    #
    # @param extractor_class [Class] the class implementing the extractor
    # @param xml [Nokogiri::XML::Document] the XML document
    # @param options_instance [Object] the options instance
    # @return [Object] an instance of the extractor class
    def self.create_extractor_instance(extractor_class, xml, options_instance)
      extractor_class.new(xml, options_instance)
    end
  end
end