Add Sparkle livecheck strategy.

Library/Homebrew/livecheck/strategy.rb

@@ -112,4 +112,5 @@ require_relative "strategy/page_match"
 require_relative "strategy/pypi"
 require_relative "strategy/follow_redirection"
 require_relative "strategy/sourceforge"
+require_relative "strategy/sparkle"
 require_relative "strategy/xorg"

Library/Homebrew/livecheck/strategy/sparkle.rb

@@ -0,0 +1,56 @@
+# typed: false
+# frozen_string_literal: true
+
+require_relative "page_match"
+
+module Homebrew
+  module Livecheck
+    module Strategy
+      # The {Sparkle} strategy fetches content at a URL and parses
+      # its contents as a Sparkle appcast in XML format.
+      #
+      # @api private
+      class Sparkle
+        extend T::Sig
+
+        NICE_NAME = "Sparkle"
+
+        PRIORITY = 1
+
+        # Whether the strategy can be applied to the provided URL.
+        sig { params(url: String).returns(T::Boolean) }
+        def self.match?(url)
+          url.match?(%r{^https?://}) &&
+            ["application/xml", "text/xml"].include?(Strategy.page_headers(url)["content-type"]) &&
+            Strategy.page_contents(url).include?("http://www.andymatuschak.org/xml-namespaces/sparkle")
+        end
+
+        # Checks the content at the URL for new versions.
+        sig { params(url: String, regex: T.nilable(Regexp)).returns(T::Hash[Symbol, T.untyped]) }
+        def self.find_versions(url, regex)
+          raise ArgumentError, "The #{NICE_NAME} strategy does not support regular expressions." if regex
+
+          require "nokogiri"
+
+          match_data = { matches: {}, regex: regex, url: url }
+
+          contents = Strategy.page_contents(url)
+
+          xml = Nokogiri.parse(contents)
+          xml.remove_namespaces!
+
+          match = xml.xpath("//rss//channel//item//enclosure")
+                     .map { |enclosure| [*enclosure["shortVersionString"], *enclosure["version"]].uniq }
+                     .reject(&:empty?)
+                     .uniq
+                     .max_by { |versions| versions.map { |v| Version.new(v) } }
+                     &.join(",")
+
+          match_data[:matches][match] = Version.new(match) if match
+
+          match_data
+        end
+      end
+    end
+  end
+end