module Tilt::CLI

def self.run(argv: ARGV, stdout: $stdout, stdin: $stdin, stderr: $stderr, script_name: File.basename($0))
  pattern = nil
  layout = nil
  locals = {}
  abort = proc do |msg|
    stderr.puts msg
    return 1
  end
  OptionParser.new do |o|
    o.program_name = script_name
    # list all available template engines
    o.on("-l", "--list") do
      groups = {}
      Tilt.lazy_map.each do |pattern,engines|
        engines.each do |engine,|
          engine = engine.split('::').last.sub(/Template\z/, '')
          (groups[engine] ||= []) << pattern
        end
      end
      groups.sort { |(k1,v1),(k2,v2)| k1 <=> k2 }.each do |engine,files|
        stdout.printf "%-20s %s\n", engine, files.sort.join(', ')
      end
      return 0
    end
    # the template type / pattern
    o.on("-t", "--type=PATTERN", String) do |val|
      abort.("unknown template type: #{val}") unless Tilt[val]
      pattern = val
    end
    # pass template output into the specified layout template
    o.on("-y", "--layout=FILE", String)  do |file|
      paths = [file, "~/.tilt/#{file}", "/etc/tilt/#{file}"]
      layout = paths.
        map  { |p| File.expand_path(p) }.
        find { |p| File.exist?(p) }
      abort.("no such layout: #{file}") if layout.nil?
    end
    # define a local variable
    o.on("-D", "--define=PAIR", String) do |pair|
      key, value = pair.split(/[=:]/, 2)
      locals[key.to_sym] = value
    end
    # define local variables from YAML or JSON
    o.on("-d", "--define-file=FILE", String) do |file|
      require 'yaml'
      abort.("no such define file: #{file}") unless File.exist? file
      hash = File.open(file, 'r:bom|utf-8') { |f| YAML.load(f.read) }
      abort.("vars must be a Hash, not instance of #{hash.class}") unless hash.is_a?(Hash)
      hash.each { |key, value| locals[key.to_sym] = value }
    end
    # define local variables using a Ruby hash
    o.on("--vars=RUBY") do |ruby|
      hash = eval(ruby)
      abort.("vars must be a Hash, not instance of #{hash.class}") unless hash.is_a?(Hash)
      hash.each { |key, value| locals[key.to_sym] = value }
    end
    o.on_tail("-h", "--help") do
      stdout.puts USAGE
      return 0
    end
  end.parse!(argv)
  file = argv.first || '-'
  pattern = file if pattern.nil?
  abort.("template type not given. see: #{script_name} --help") if ['-', ''].include?(pattern)
  engine = Tilt[pattern]
  abort.("template engine not found for: #{pattern}") unless engine
  template =
    engine.new(file) {
      if file == '-'
        stdin.read
      else
        File.read(file)
      end
    }
  output = template.render(self, locals)
  # process layout
  output = Tilt.new(layout).render(self, locals) { output } if layout
  stdout.write(output)
  0
end