module GLI
  # Class to encapsulate stuff about the terminal.  This is a singleton, mostly to facilitate testing.
  #
  # Example:
  #
  #     Terminal.instance.size[0] # => columns in the terminal
  #     Terminal.default_size = [128,24] # => change default when we can't figure it out
  #     raise "no ls?!?!?" unless Terminal.instance.command_exists?("ls")
  #
  class Terminal

    @@default_size = [80,24]

    # Get the default size of the terminal when we can't figure it out
    # 
    # Returns an array of int [cols,rows]
    def self.default_size
      @@default_size
    end

    # Set the default size of the terminal to use when we can't figure it out
    #
    # size - array of two int [cols,rows]
    def self.default_size=(size)
      @@default_size = size
    end

    # Provide access to the shared instance
    def self.instance; @@instance ||= Terminal.new; end

    # Call this to cause methods to throw exceptions rather than return a sane default.  You
    # probably don't want to call this unless you are writing tests
    def make_unsafe!;
      @unsafe = true
    end

    # Returns true if the given command exists on this system
    #
    # command - The command to check for
    def command_exists?(command)
      ENV['PATH'].split(File::PATH_SEPARATOR).any? {|d| File.exists? File.join(d, command) }
    end

    # Ripped from hirb https://github.com/cldwalker/hirb/blob/master/lib/hirb/util.rb
    # Returns an array of size two ints representing the terminal width and height
    def size
      if (ENV['COLUMNS'] =~ /^\d+$/) && (ENV['LINES'] =~ /^\d+$/)
        [ENV['COLUMNS'].to_i, ENV['LINES'].to_i]
      elsif (jruby? || (!STDIN.tty? && ENV['TERM'])) && command_exists?('tput')
        [run_command('tput cols').to_i, run_command('tput lines').to_i]
      elsif STDIN.tty? && command_exists?('stty')
        run_command('stty size').scan(/\d+/).map { |s| s.to_i }.reverse
      else
        Terminal.default_size
      end
    rescue Exception => ex
      raise ex if @unsafe
      Terminal.default_size
    end

    private

    # Runs a command using backticks.  Extracted to allow for testing
    def run_command(command)
      `#{command}`
    end

    # True if we are JRuby; exposed to allow for testing
    def jruby?; RUBY_PLATFORM =~ /java/; end

  end
end