require 'digest/md5'

# Throttle arbituary operation. Once limit is reached it will raise a
# Throttle::LimitExeeded exception.
#
# Example:
#
#   Throttle.for("feed:#{request.remote_ip}", :max => 20, :in => 10.minutes) do
#     render :xml => Articles.all
#   end
#
#   If you want to clear the timeout for the current block ( for example: fraud protection. Clear the throttle when
#   the submitted Credit Card was valid. ) your block can accept a yielded throttle object and call the clear method
#
#   Throttle.for("cc:#{request.remote_ip}", :max => 20, :in => 10.minutes) do |throttle|
#     if am.pay(@credit_card)
#       throttle.clear
#       redirect_to :action => 'done'
#     end
#   end
#
class Throttle
  class LimitExceeded < StandardError
  end

  def self.for(key, options = {})
    throttle = self.new(key, options)
    if ActionController::Base.perform_caching
      throttle.increment_counter
    end

    yield throttle
  end

  def initialize(key, options)
    @key  =  key.blank? ? nil : "throttle:#{Digest::MD5.hexdigest(key.to_s)}"
    @max, @timeout = options[:max].to_i, options[:in].to_i
  end

  def increment_counter
    return if @key.blank?

    count = Rails.cache.increment(@key)

    if count.nil?
      Rails.cache.write @key, 1, :expires_in => @timeout
    elsif @max <= count
      raise LimitExceeded, "Too many requests for operation"
    end
  end

  def clear
    return if @key.blank?
    return unless ActionController::Base.perform_caching

    Rails.cache.delete @key
    true
  end

end