sources: factor out Source::URL::Newgrounds.

Also fix it so that the image URL is set as the source for Newgrounds
posts, not the page URL. It's possible to generate the page URL from the
image URL (except for images after the first in multi-image posts).

* Page: https://www.newgrounds.com/art/view/natthelich/weaver
* Image: https://art.ngfiles.com/images/1520000/1520217_natthelich_weaver.jpg?f1606365031

app/logical/source/url.rb

@@ -20,6 +20,7 @@ module Source
     SUBCLASSES = [
       Source::URL::Twitter,
       Source::URL::HentaiFoundry,
+      Source::URL::Newgrounds,
       Source::URL::Plurk,
       Source::URL::Skeb,
       Source::URL::TwitPic,

app/logical/source/url/newgrounds.rb

@@ -0,0 +1,92 @@
+# frozen_string_literal: true
+
+# Image Urls
+#
+# * https://art.ngfiles.com/images/1543000/1543982_natthelich_pandora-2.jpg?f1607971817
+# * https://art.ngfiles.com/images/1033000/1033622_natthelich_fire-emblem-marth-plus-progress-pic.png?f1569487181
+#
+# * https://www.newgrounds.com/art/view/natthelich/weaver (page)
+# * https://art.ngfiles.com/images/1520000/1520217_natthelich_weaver.jpg?f1606365031
+# * https://art.ngfiles.com/comments/57000/iu_57615_7115981.jpg
+#
+# Thumbnail URLs
+#
+# * https://art.ngfiles.com/thumbnails/1543000/1543982_full.png?f1607971901
+# * https://art.ngfiles.com/thumbnails/1254000/1254985.png?f1588263349
+#
+# Page URLs
+#
+# * https://www.newgrounds.com/art/view/puddbytes/costanza-at-bat
+# * https://www.newgrounds.com/art/view/natthelich/weaver (multiple)
+#
+# Video URLs
+#
+# * https://www.newgrounds.com/portal/view/825916 (page)
+# * https://picon.ngfiles.com/825000/flash_825916_card.png?f1639666239 (poster)
+# * https://uploads.ungrounded.net/alternate/1801000/1801343_alternate_165104.1080p.mp4?1639666238
+# * https://uploads.ungrounded.net/alternate/1801000/1801343_alternate_165104.720p.mp4?1639666238
+# * https://uploads.ungrounded.net/alternate/1801000/1801343_alternate_165104.360p.mp4?1639666238
+#
+# Flash URLs
+#
+# * https://www.newgrounds.com/portal/view/225625 (page)
+# * https://uploads.ungrounded.net/225000/225625_colormedressup.swf?1111143751 (file)
+#
+# Other URLs
+#
+# * https://www.newgrounds.com/reviews/portal/1543982/4/
+# * https://www.newgrounds.com/reviews/portal/1543982/4/score/1
+# * https://www.newgrounds.com/content/share/1543982/4/
+# * https://www.newgrounds.com/favorites/content/who/1543982/4
+#
+# Profile URLs
+#
+# * https://natthelich.newgrounds.com
+# * https://natthelich.newgrounds.com/art
+#
+class Source::URL::Newgrounds < Source::URL
+  attr_reader :username, :work_id, :work_title
+
+  def self.match?(url)
+    url.domain.in?(["newgrounds.com", "ngfiles.com", "ungrounded.net"])
+  end
+
+  def parse
+    case [host, *path_segments]
+
+    # https://www.newgrounds.com/art/view/puddbytes/costanza-at-bat
+    # https://www.newgrounds.com/art/view/natthelich/fire-emblem-marth-plus-progress-pic
+    in "www.newgrounds.com", "art", "view", username, work_title
+      @username = username
+      @work_title = work_title
+
+    # https://art.ngfiles.com/images/1254000/1254722_natthelich_pandora.jpg
+    # https://art.ngfiles.com/images/1033000/1033622_natthelich_fire-emblem-marth-plus-progress-pic.png?f1569487181
+    in "art.ngfiles.com", "images", _, /^(\d+)_([^_]+)_(.*)\.\w+$/ => filename
+      @work_id = $1
+      @username = $2
+      @work_title = $3
+      @filename = filename
+
+    # https://art.ngfiles.com/thumbnails/1254000/1254985.png?f1588263349
+    in "art.ngfiles.com", "thumbnails", _, /^(\d+)\.\w+$/ => filename
+      @work_id = $1
+      @filename = filename
+
+    # https://art.ngfiles.com/comments/57000/iu_57615_7115981.jpg
+    in "art.ngfiles.com", "comments", _, /^iu/ => filename
+      @filename = filename
+
+    # https://natthelich.newgrounds.com
+    # https://natthelich.newgrounds.com/art/
+    in /^([a-z0-9-]+)\.newgrounds\.com$/, *rest if host != "www.newgrounds.com"
+      @username = $1
+
+    else
+    end
+  end
+
+  def image_url?
+    url.host == "art.ngfiles.com"
+  end
+end