media_list.rb

class MediaList

  # File extensions.
  TYPES = {
    :audio => [
      'aac',
      'aif',
      'flac',
      'mp3',
      'oga',
      'ogg',
      'wav',
      'wma',
    ],

    :video => [
      'avi',
      'mp4',
      'mpeg',
      'mov',
      'ogv',
    ]
  }

  def self.show_help(error = nil)
    $stderr.puts(error) if error
    $stderr.puts("Usage: #{$0} <audio|video> </path/to/media>")
    exit
  end

  def show_help(*args)
    self.class.show_help(*args)
  end

  def initialize(args)
    @type, @path = validate(args)
    @files = []
  end

  def print
    header = "#{@type} media in #{@path}:"
    $stdout.puts(header)
    $stdout.puts('-' * header.size)

    read_files if @files.empty?
    @files.each { |file| $stdout.puts(file) }
  end

  def read_files
    Dir["#{@path}/**/*"].each do |full_path|
      next if File.directory?(full_path)

      extname = File.extname(full_path).gsub(/^[.]/, '')
      case @type
      when 'audio'
        @files << name_for(full_path) if TYPES[:audio].include?(extname)
      when 'video'
        @files << name_for(full_path) if TYPES[:video].include?(extname)
      else
        raise "Unknown type: #{@type}"
      end
    end
  end

  private

  def name_for(full_path)
    full_path.gsub(/#{@path}\//, '')
  end

  def validate(args)
    show_help unless args[0] && args[1]
    type = validate_type(args[0])
    path = validate_path(args[1])
    [ type, path ]
  end

  def validate_type(type_name)
    unless (type_name == 'audio') || (type_name == 'video')
      show_help("Type must be: 'audio' or 'video'")
    end
    type_name.downcase
  end

  def validate_path(path)
    full_path = File.expand_path(path)
    unless File.exists?(full_path)
      show_help("Directory not found: #{full_path}")
    end
    full_path
  end

end

if $0 == __FILE__
  if ARGV.size < 2
    MediaList.show_help
  end

  MediaList.new(ARGV).print
end