require 'nagios'

module Nagios
  # Keep track of last parsed time and last changed time of the
  # status/cache file to avoid parsing on each HTTP request.
  module TimedParse

    # Set some minimum interval for re-parsing of the status file:
    # even if file changes often, we do not want to parse it more
    # often, then this number of seconds.

    TTL = ::DEFAULT[:ttl] || 0

    # Override constructor and parse method from ::Nagios::Objects or
    # ::Nagios::Status classes, add instance variables to handle
    # modification and parseing times of status file.
    # Original methods are aliased:
    # - initialize -> constructor
    # - parse -> parse!
    # See also
    # http://www.ruby-forum.com/topic/969161
    def self.included(base)
      base.class_eval do
        alias_method :parse!, :parse
        alias_method :constructor, :initialize

        # @method initialize
        # Extend current constructor with some additional data to
        # track file change time
        #
        # @param [String] file Path to status file
        # @param [Fixnum] parse_interval Number of seconds between
        #     re-parsing of the file
        def initialize(file, parse_interval=TTL)
          constructor(file)

          # Time when status file was last time parsed, set it to 0 secs
          # epoch to make sure it will be parsed
          @last_parsed = Time.at(0)

          # Last time file was changed
          @last_changed = File.mtime(@path)
          @parse_interval = parse_interval
        end


        # Extend original parse method: parse file only if it needs
        # parsing and set time of parser run to current time.
        def parse
          if need_parsing?
            parse!
            @last_parsed = Time.now
          end
        end
      end
    end

    attr_accessor :last_parsed, :parse_interval
      
    def last_changed
      @last_changed = File.mtime(@path)
    end

    # Return true if file is changed since it was parsed last time
    def changed?
      self.last_changed > self.last_parsed
    end
    
    # Check if:
    # - file changed?
    # - was it parsed recently?
    def need_parsing?
      changed? && ((Time.now - self.last_parsed) > @parse_interval)
    end
    
  end
end