require "retries/version"

class Retries
  class << self
    # You can use this to turn off all sleeping in with_retries. This can be useful in tests. Defaults to
    # `true`.
    attr_accessor :sleep_enabled
  end
end

Retries.sleep_enabled = true

module Kernel
  # Runs the supplied code block an retries with an exponential backoff.
  #
  # @param [Hash] options the retry options.
  # @option options [Fixnum] :max_tries (3) The maximum number of times to run the block.
  # @option options [Float] :base_sleep_seconds (0.5) The starting delay between retries.
  # @option options [Float] :max_sleep_seconds (1.0) The maximum to which to expand the delay between retries.
  # @option options [Proc] :handler (nil) If not `nil`, a `Proc` that will be called for each retry. It will be
  #         passed two arguments, `exception` (the rescued exception) and `attempt_number`.
  # @option options [Exception, <Exception>] :rescue (StandardError) This may be a specific exception class to
  #         rescue or an array of classes.
  # @yield [attempt_number] The (required) block to be executed, which is passed the attempt number as a
  #         parameter.
  def with_retries(options = {}, &block)
    # Check the options and set defaults
    options_error_string = "Error with options to with_retries:"
    max_tries = options[:max_tries] || 3
    raise "#{options_error_string} :max_tries must be greater than 0." unless max_tries > 0
    base_sleep_seconds = options[:base_sleep_seconds] || 0.5
    max_sleep_seconds = options[:max_sleep_seconds] || 1.0
    if base_sleep_seconds > max_sleep_seconds
      raise "#{options_error_string} :base_sleep_seconds cannot be greater than :max_sleep_seconds."
    end
    handler = options[:handler]
    exception_types_to_rescue = options[:rescue] || StandardError
    exception_types_to_rescue = [exception_types_to_rescue] unless exception_types_to_rescue.is_a?(Array)
    raise "#{options_error_string} with_retries must be passed a block" unless block_given?

    # Let's do this thing
    attempts = 0
    begin
      attempts += 1
      return block.call(attempts)
    rescue *exception_types_to_rescue => exception
      raise exception if attempts >= max_tries
      handler.call(exception, attempts) if handler
      # Don't sleep at all if sleeping is disabled (used in testing).
      if Retries.sleep_enabled
        # The sleep time is an exponentially-increasing function of base_sleep_seconds. But, it never exceeds
        # max_sleep_seconds.
        sleep_seconds = [base_sleep_seconds * (2 ** (attempts - 1)), max_sleep_seconds].min
        # Randomize to a random value in the range sleep_seconds/2 .. sleep_seconds
        sleep_seconds = sleep_seconds * (0.5 * (1 + rand()))
        # But never sleep less than base_sleep_seconds
        sleep_seconds = [base_sleep_seconds, sleep_seconds].max
        sleep sleep_seconds
      end
      retry
    end
  end
end