LRU Memory Store

LRU Memory Store

class LRUMemoryStore < ActiveSupport::Cache::Store

  def initialize(max_size = 1000)
    @max_size = max_size
    @data = {}
    @lru = []
  end

  def read(name, options = nil)
    super
    set_lru(name)
    @data[name]
  end

  def write(name, value = nil, options = nil)
    super
    value = name if value.nil?
    @data[name] = value.freeze
    set_lru(name)
    @data.delete(@lru.pop) if @lru.size > @max_size
  end

  def delete(name, options = nil)
    super
    @data.delete(name)
    @lru.delete(name)
  end

  def delete_matched(matcher, options = nil)
    raise 'not implemented'
  end

  def exist?(name, options = nil)
    super
    @data.has_key?(name)
  end

  def clear
    @data.clear
    @lru.clear
  end

  def size
    raise 'Index does not match data size.' if @data.size != @lru.size
    @data.size
  end

  private

  def set_lru(key)
    @lru.unshift(@lru.delete(key) || key)
  end

end