Implement puppet-metadata with various subcommands

This implements a puppet-metadata executable which now only implements
the eol command to show which operating systems in metadata are end of
life.

bin/puppet-metadata

@@ -0,0 +1,69 @@
+#!/usr/bin/env ruby
+require 'optparse'
+require 'json'
+require 'puppet_metadata'
+
+class Command
+  def initialize(arguments); end
+
+  def metadata
+    @metadata ||= begin
+      @filename = 'metadata.json' if @filename.nil? || @filename.empty?
+
+      PuppetMetadata.read(@filename)
+    end
+  rescue StandardError => e
+    warn "Failed to read #{filename}: #{e}"
+    exit 2
+  end
+
+  def self.commands
+    Command.subclasses.to_h { |subclass| [subclass.command, subclass] }
+  end
+
+  def self.command
+    name.gsub(/Command$/, '')
+        .gsub(/([A-Z]+)([A-Z][a-z])/, '\1_\2')
+        .gsub(/([a-z\d])([A-Z])/, '\1_\2')
+        .downcase
+  end
+
+  def self.parser
+    raise NotImplementedError
+  end
+end
+
+class EolCommand < Command
+  def initialize(arguments)
+    super
+
+    @filename = arguments.shift
+
+    # TODO: expose --at $DATE
+    eol = metadata.eol_operatingsystems
+
+    if eol.any?
+      width = eol.each_key.map(&:length).max
+
+      puts 'Found EOL operating systems'
+      eol.each do |os, versions|
+        puts "#{os.ljust(width)} #{versions.join(', ')}"
+      end
+    else
+      puts 'All operating systems up to date'
+    end
+  end
+end
+
+def main
+  command = ARGV[0]
+  command_class = Command.commands[command]
+  unless command_class
+    warn "Command '#{command}' not understood."
+    exit 2
+  end
+
+  command_class.new(ARGV[1..])
+end
+
+main

puppet_metadata.gemspec

@@ -13,6 +13,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = Gem::Requirement.new('>= 2.7', '< 4')
 
   s.executables << 'metadata2gha'
+  s.executables << 'puppet-metadata'
   s.files = Dir['lib/**/*.rb']
   s.extra_rdoc_files = ['README.md']
   s.rdoc_options << '--main' << 'README.md'