Fix #3877: Add sta.sh strategy.

Co-authored-by: lllusion3469 <31420484+lllusion3469@users.noreply.github.com>

app/logical/sources/strategies/stash.rb

@@ -0,0 +1,39 @@
+module Sources
+  module Strategies
+    class Stash < DeviantArt
+      STASH = %r{\Ahttps?://sta\.sh/(?<post_id>[0-9a-zA-Z]+)}i
+
+      def self.match?(*urls)
+        urls.compact.any? { |x| x =~ STASH }
+      end
+
+      def site_name
+        "Sta.sh"
+      end
+
+      def canonical_url
+        page_url
+      end
+
+      def page_url
+        "https://sta.sh/#{stash_id}"
+      end
+
+      def api_url
+        page_url
+      end
+
+      def self.stash_id_from_url(url)
+       if url =~ STASH
+         $~[:post_id].downcase
+       else
+         nil
+       end
+     end
+
+      def stash_id
+        [url, referer_url].map{ |x| self.class.stash_id_from_url(x) }.compact.first
+      end
+    end
+  end
+end