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/art_station.rb

@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+# @see Source::URL::ArtStation
+class Source::Extractor
+  class ArtStation < Source::Extractor
+    def match?
+      Source::URL::ArtStation === parsed_url
+    end
+
+    def image_urls
+      if parsed_url.image_url?
+        [asset_url(url)]
+      else
+        image_urls_from_api
+      end
+    end
+
+    def page_url
+      return nil if project_id.blank?
+
+      if artist_name.present?
+        "https://#{artist_name}.artstation.com/projects/#{project_id}"
+      else
+        "https://www.artstation.com/artwork/#{project_id}"
+      end
+    end
+
+    def profile_url
+      return nil if artist_name.blank?
+      "https://www.artstation.com/#{artist_name}"
+    end
+
+    def artist_name
+      artist_name_from_url || api_response.dig(:user, :username)
+    end
+
+    def artist_commentary_title
+      api_response[:title]
+    end
+
+    def artist_commentary_desc
+      api_response[:description]
+    end
+
+    def dtext_artist_commentary_desc
+      ActionView::Base.full_sanitizer.sanitize(artist_commentary_desc)
+    end
+
+    def tags
+      api_response[:tags].to_a.map do |tag|
+        [tag, "https://www.artstation.com/search?q=" + CGI.escape(tag)]
+      end
+    end
+
+    def image_urls_from_api
+      api_response[:assets].to_a.map do |asset|
+        if asset[:asset_type] == "image"
+          asset_url(asset[:image_url])
+        elsif asset[:asset_type] == "video_clip"
+          next # XXX Skip for now; actually downloading these videos requires bypassing a Cloudflare captcha.
+
+          url = Nokogiri::HTML5.parse(asset[:player_embedded]).at("iframe").attr("src")
+          next if url.nil?
+
+          response = http.cache(1.minute).get(url)
+          next if response.status != 200
+
+          response.parse.at("video source").attr("src")
+        end
+      end.compact
+    end
+
+    def artist_name_from_url
+      parsed_url.username || parsed_referer&.username
+    end
+
+    def project_id
+      parsed_url.work_id || parsed_referer&.work_id
+    end
+
+    def api_response
+      return {} if project_id.blank?
+
+      resp = http.cache(1.minute).get("https://www.artstation.com/projects/#{project_id}.json")
+      return {} if resp.code != 200
+
+      resp.parse.with_indifferent_access
+    end
+    memoize :api_response
+
+    def asset_url(url)
+      parsed_url = Source::URL.parse(url)
+
+      image_sizes = %w[original 4k large medium small]
+      urls = image_sizes.map { |size| parsed_url.full_image_url(size) }
+
+      chosen_url = urls.find { |url| http_exists?(url) }
+      chosen_url || url
+    end
+  end
+end