module Rib; end
module Rib::API
  def before_loop
    read_history
    self
  end

  def in_loop
    input = catch(:rib_exit){ loop_once while true }
    puts if input == nil
  end

  # Runs through one loop iteration: gets input, evals and prints result
  def loop_once
    self.error_raised = nil
    input = get_input
    throw(:rib_exit, input) if config[:exit].include?(input)
    if input.strip == ''
      eval_input(input)
    else
      print_result(eval_input(input))
    end
  rescue Interrupt
    handle_interrupt
  end

  # Handles interrupt (Control-C) by printing a newline
  def handle_interrupt() puts end

  # Sets @result to result of evaling input and print unexpected errors
  def eval_input(input)
    loop_eval(input)
  rescue Exception => e
    self.error_raised = true
    print_eval_error(e)
  ensure
    config[:line] += 1
  end

  # When extending this method, ensure your plugin disables readline:
  # Readline.config[:readline] = false.
  # @return [String, nil] Prints #prompt and returns input given by user
  def get_input
    print(prompt)
    if input = $stdin.gets
      input.chomp
    else
      nil
    end
  end

  # @return [String]
  def prompt
    config[:prompt]
  end

  def read_history
  end

  def write_history
  end

  def history
    @history ||= []
  end

  # Evals user input using @binding, @name and @line
  def loop_eval(input)
    config[:binding].eval(input, "(#{config[:name]})", config[:line])
  end

  # Prints error formatted by #format_error to STDERR. Could be extended to
  # handle certain exceptions.
  # @param [Exception]
  def print_eval_error(err)
    warn format_error(err)
  end

  # Prints result using #format_result
  def print_result(result)
    puts(format_result(result)) unless error_raised
  rescue StandardError, SyntaxError => e
    warn "#{config[:name]}: Error while printing result:\n" \
         "#{format_error(e)}"
  end

  # Formats errors raised by eval of user input
  # @param [Exception]
  # @return [String]
  def format_error(e)
    "#{e.class}: #{e.message}\n    #{e.backtrace.join("\n    ")}"
  end

  # @return [String] Formats result using result_prompt
  def format_result(result)
    config[:result_prompt] + result.inspect
  end

  # Called after shell finishes looping.
  def after_loop
    write_history
    self
  end
end