sliding_window_map.rb

# By Pseudon Mousie
class SlidingWindowMap

  # Create a hash, with the keys as keys
  # The values will be the timestamps when the key was used.
  def initialize(keys, max_count, period_ms, verbose=false)
    @verbose = verbose
    @key_counts = Hash.new
    keys.each{|key|
      @key_counts[key] = []
    }
    @max_count = max_count
    # store period in floating point seconds to match Time objects
    @period_f_sec = period_ms / 1000.0
    puts "keycounts:#{@key_counts.inspect}..." if @verbose
  end

  def getNextKey()
    @key_counts.keys.each{|key|
    puts "checking #{key}..." if @verbose
      return key if has_uses_remaining?(key)
    }
    nil
  end

  # Calling this function counts as a "use"
  # unless there are no uses available.
  def has_uses_remaining?(key)
    times_used = @key_counts[key]
    # Clear out expired uses
    while !(times_used.empty?) && (times_used.first < Time.now)
      times_used.shift
    end
    if times_used.length < @max_count
      times_used.push(Time.now + @period_f_sec)
      return true
    else
      return false
    end
  end
end