find_appcast: detect electron-builder appcasts (#69968)

* find_appcast: detect electron-builder appcasts

Fixes Homebrew/homebrew-cask#69749.

* find_appcast: address @vitorgalvao's comments

developer/bin/find_appcast

@@ -69,6 +69,18 @@ function find_devmate {
   verify_appcast 'DevMate' "${url}"
 }
 
+function find_electron_builder {
+  local app url
+
+  app="${1}"
+
+  electron_parser_script="$(brew --repo homebrew/cask)/developer/bin/parse_electron_builder_appcast"
+
+  url="$("${electron_parser_script}" "${app}")"
+
+  verify_appcast 'electron-builder' "${url}"
+}
+
 # Exit if no argument (or more than one) was given
 if [[ -z "${1}" ]] || [[ -n "${2}" ]]; then
   usage
@@ -86,3 +98,4 @@ fi
 find_sparkle "${path_to_app}"
 find_hockeyapp "${path_to_app}"
 find_devmate "${path_to_app}"
+find_electron_builder "${path_to_app}"

developer/bin/parse_electron_builder_appcast

@@ -0,0 +1,42 @@
+#!/usr/bin/env ruby
+
+require "pathname"
+require "yaml"
+
+def parse(app_path)
+  appcast_url = Pathname.new "#{app_path}/Contents/Resources/app-update.yml"
+
+  exit 2 unless appcast_url.exist?
+
+  data = YAML.load_file appcast_url
+
+  case data["provider"]
+  when "github"
+    owner = data["owner"]
+    repo = data["repo"]
+    puts "https://github.com/#{owner}/#{repo}/releases.atom"
+  when "s3"
+    bucket = data["bucket"]
+    channel = data["channel"]
+    puts "https://#{bucket}.s3.amazon-aws.yml/#{channel}/latest-mac.yml"
+  end
+end
+
+###
+### main
+###
+
+usage = <<~EOS
+  Usage: parse_electron_builder_appcast <application.app>
+
+  Given an Application name or a path to an Application, attempt to parse the
+  included 'app-update.yml' manifest and output the appcast URL.
+
+EOS
+
+unless ARGV.length == 1
+  puts usage
+  exit 1
+end
+
+parse(ARGV[0])