sources: rename Sources::Strategies to Source::Extractor.

Rename Sources::Strategies to Source::Extractor. A Source::Extractor
represents a thing that extracts information from a given URL.

app/logical/source/extractor/newgrounds.rb

@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+# @see Source::URL::Newgrounds
+module Source
+  class Extractor
+    class Newgrounds < Source::Extractor
+      def match?
+        Source::URL::Newgrounds === parsed_url
+      end
+
+      def image_urls
+        if parsed_url.image_url?
+          [url]
+        else
+          urls = []
+
+          urls += page&.css(".image img").to_a.map { |img| img["src"] }
+          urls += page&.css("#author_comments img[data-user-image='1']").to_a.map { |img| img["data-smartload-src"] || img["src"] }
+
+          urls.compact
+        end
+      end
+
+      def page_url
+        return nil if illust_title.blank? || user_name.blank?
+
+        "https://www.newgrounds.com/art/view/#{user_name}/#{illust_title}"
+      end
+
+      def page
+        return nil if page_url.blank?
+
+        response = http.cache(1.minute).get(page_url)
+        return nil if response.status == 404
+
+        response.parse
+      end
+      memoize :page
+
+      def tags
+        page&.css("#sidestats .tags a").to_a.map do |tag|
+          [tag.text, "https://www.newgrounds.com/search/conduct/art?match=tags&tags=" + tag.text]
+        end
+      end
+
+      def normalize_tag(tag)
+        tag = tag.tr("-", "_")
+        super(tag)
+      end
+
+      def artist_name
+        name = page&.css(".item-user .item-details h4 a")&.text&.strip || user_name
+        name&.downcase
+      end
+
+      def other_names
+        [artist_name, user_name].compact.uniq
+      end
+
+      def profile_url
+        # user names are not mutable, artist names are.
+        # However we need the latest name for normalization
+        "https://#{artist_name}.newgrounds.com"
+      end
+
+      def artist_commentary_title
+        page&.css(".pod-head > [itemprop='name']")&.text
+      end
+
+      def artist_commentary_desc
+        page&.css("#author_comments")&.to_html
+      end
+
+      def dtext_artist_commentary_desc
+        DText.from_html(artist_commentary_desc)
+      end
+
+      def user_name
+        parsed_url.username || parsed_referer&.username
+      end
+
+      def illust_title
+        parsed_url.work_title || parsed_referer&.work_title
+      end
+    end
+  end
+end