Add Rule34.us support.

app/logical/source/url/rule34_dot_us.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+# https://rule34.us is running a modified fork of Gelbooru 0.1, so its URL structure is similar but not identical to
+# that of other Gelbooru-based sites.
+#
+# @see Source::URL::Gelbooru
+class Source::URL::Rule34DotUs < Source::URL
+  attr_reader :post_id, :md5, :image_type, :full_image_url
+
+  def self.match?(url)
+    url.domain.in?(%w[rule34.us])
+  end
+
+  def parse
+    case [domain, *path_segments]
+
+    # https://rule34.us/index.php?r=posts/view&id=6204967
+    in _, "index.php" if params[:r] == "posts/view" && params[:id].present?
+      @post_id = params[:id].to_i
+
+    # https://rule34.us/hotlink.php?hash=236690fd962fa394edf9894450261dac
+    in _, "hotlink.php" if params[:hash]&.match?(/\A\h{32}\z/)
+      @md5 = params[:hash]
+
+    # https://img2.rule34.us/thumbnails/23/66/thumbnail_236690fd962fa394edf9894450261dac.jpg
+    # https://img2.rule34.us/images/23/66/236690fd962fa394edf9894450261dac.png
+    # https://video.rule34.us/images/d8/1d/d81d79f0292cdb096a8653efa001342d.webm
+    # no samples
+    in _, ("images" | "thumbnails") => image_type, /\A\h{2}\z/ => h1, /\A\h{2}\z/ => h2, /\A(?:thumbnail_)?(\h{32})\.\w+\z/i
+      @md5 = $1
+      @image_type = image_type
+      @full_image_url = url.to_s if image_type == "images"
+
+    else
+      nil
+    end
+  end
+
+  def image_url?
+    image_type.present?
+  end
+
+  def page_url
+    if post_id.present?
+      "https://rule34.us/index.php?r=posts/view&id=#{post_id}"
+    elsif md5.present?
+      "https://rule34.us/hotlink.php?hash=#{md5}"
+    end
+  end
+end