module Parliament
  module Utils
    module Helpers
      module ApplicationHelper
        # What MIME types does the API accept?
        #
        # Note: All of the below are used to generate MIME types that our application will answer to, but NOT the
        # alternatives shown in our header. See ALTERNATIVE_MIME_TYPE_CONFIG.
        API_MIME_TYPE_CONFIG = [
            {
                nt: 'application/n-triples'
            },
            {
                ttl: 'text/turtle'
            },
            {
                tsv: 'text/tab-separated-values'
            },
            {
                csv: 'text/csv'
            },
            {
                rj: 'application/json+rdf'
            },
            {
                jsonld: 'application/json+ld',
                json:   'application/json'
            },
            {
                rdfxml: 'application/rdf+xml',
                rdf:    'application/xml',
                xml:    'text/xml'
            }
        ].freeze

        # Use the above, minus the last two entries (json & xml), to build an alternative URL list.
        # Then re-create JSON and XML with the correct alternatives
        ALTERNATIVE_MIME_TYPE_CONFIG = API_MIME_TYPE_CONFIG.take(API_MIME_TYPE_CONFIG.size-2).concat(
            [
                {
                    json: 'application/json+ld'
                },
                {
                    xml: 'application/rdf+xml'
                }
            ]
        )

        API_MIME_TYPES                   = Parliament::Utils::Helpers::ApplicationHelper::API_MIME_TYPE_CONFIG.map { |mime_type| mime_type.values }.flatten.freeze
        API_FILE_EXTENSIONS              = Parliament::Utils::Helpers::ApplicationHelper::API_MIME_TYPE_CONFIG.map { |mime_type| mime_type.keys   }.flatten.freeze
        ALTERNATIVE_MIME_TYPES_FLATTENED = Parliament::Utils::Helpers::ApplicationHelper::ALTERNATIVE_MIME_TYPE_CONFIG.reduce(:merge)

        # Sets the title for a page.
        #
        # @param [String] page_title the title of the page.
        # @return [String] the title of the page.
        def title(page_title)
          content_for(:title) { page_title }
          page_title
        end
        # Before every request that provides data, see if the user is requesting a format that can be served by the data API.
        # If they are, transparently redirect them with a '302: Found' status code
        def data_check
          # Check format to see if it is available from the data API
          # We DO NOT offer data formats for constituency maps
          return if !API_MIME_TYPES.include?(request.formats.first) || (params[:controller] == 'constituencies' && params[:action] == 'map')

          # Find the current controller/action's API url
          @data_url = data_url

          # Catch potential nil values
          raise StandardError, 'Data URL does not exist' if @data_url.nil?

          # Get the requested type
          response.headers['Accept'] = request.formats.first.to_s

          # Set redirect_url as URI object
          redirect_url = URI(@data_url.call(params).query_url)

          # Get the request url as a URI object
          request_extension = File.extname(URI.parse(request.url).path)
          redirect_url.path = redirect_url.path + request_extension if request_extension != ''

          return redirect_to(redirect_url.to_s)
        end

        # Get the data URL for our current controller and action OR raise a StandardError
        #
        # @raises [StandardError] if there is no Proc available for a controller and action pair, we raise a StandardError
        #
        # @return [Proc] a Proc which can be called to generate a data URL
        def data_url
          self.class::ROUTE_MAP[params[:action].to_sym] || raise(StandardError, "You must provide a ROUTE_MAP proc for #{params[:controller]}##{params[:action]}")
        end

        # Populates @request with a data url which can be used within controllers.
        def build_request
          @request = data_url.call(params)

          populate_alternates(@request.query_url)
        end

        # Populates Pugin.alternates with a list of data formats and corresponding urls
        #
        # @param [String] url the url where alternatives can be found
        def populate_alternates(url)
          alternates = []

          ALTERNATIVE_MIME_TYPES_FLATTENED.each do |extension, format| # (key, value)
            uri =  URI.parse(url)
            uri.path = "#{uri.path}.#{extension}"

            alternates << { type: format, href: uri.to_s }
          end

          Pugin.alternates = alternates
        end

        private

        # Before every request, reset Pugin's list of alternates to prevent showing rel-alternate tags on pages without data
        def reset_alternates
          Pugin.alternates = []
        end

      end
    end
  end
end