module BitPlayer
  # Business rules for proceeding statefully through an application.
  class Navigator
    RenderOptions = Struct.new(
      :view_context, :app_context, :position, :participant
    )

    def initialize(participant)
      @participant = participant
      @status = participant.navigation_status
    end

    def context
      @status.context
    end

    def module_position
      @status.module_position
    end

    def provider_position
      @status.provider_position
    end

    def content_position
      @status.content_position
    end

    def render_current_content(view_context)
      options = RenderOptions.new(
        view_context, context, content_position, @participant
      )

      current_content_provider.render_current(options)
    end

    def show_nav_link?
      current_content_provider.show_nav_link?
    end

    def current_content_provider
      current_module.provider(provider_position)
    end

    def fetch_next_content
      if current_content_provider.exists?(content_position + 1)
        @status.increment_content_position
      elsif current_module.provider_exists?(provider_position + 1)
        @status.increment_provider_position
      else
        initialize_context(context)
      end
    end

    def initialize_context(context)
      @status.initialize_context(context)
    end

    def initialize_location(options)
      content_module = ContentModule.find(options[:module_id])
      @status.context = content_module.context
      @status.module_position = content_module.position
      @status.provider_position = 1
      if options[:provider_id]
        @status.provider_position = content_module.content_providers
          .find(options[:provider_id]).position
      end
      @status.content_position = [options[:content_position].to_i, 1].max
      @status.save
    end

    def current_module
      @current_module ||= nil

      module_attrs = { context: context, position: module_position }

      if current_module_stale?
        @current_module = ContentModule.where(module_attrs).first
      end

      @current_module ||= ContentModule.new(module_attrs)
    end

    private

    def current_module_stale?
      @current_module.nil? ||
        (@current_module.context != context ||
         @current_module.position != module_position)
    end
  end
end