class LocalFileStoreApp
  class CachedFileStore
    CACHE_SIZE=30000
    DEFAULT_WRITE_DELAY=30

    def initialize(store,writeDelay=nil,cacheSize=nil)
      @writeDelay=writeDelay
      @writeDelay||=DEFAULT_WRITE_DELAY
      
      @cacheSize=cacheSize
      @cacheSize||=CACHE_SIZE
      
      @store=store
      
      @dataCache={}
      @dataAccessTime={}
      @dataWriteTime={}
      @lastWrite=nil
      
      @mutex=Mutex.new
    end
    def []=(name,value)
      @mutex.synchronize {
        @dataCache[name]=value
        @dataAccessTime[name]=Time.now
        @dataWriteTime[name]=Time.now
        checkWriteCache
      }
    end
    def [](name)
      @mutex.synchronize {
        unless @dataCache.key?(name)
          @dataCache[name]=@store[name]
          @dataAccessTime[name]=Time.now
        end
        d=@dataCache[name]
        checkWriteCache
        d
      }
    end
    
    def rm(name)
      @store.rm(name)
    end
    
    def flush
      @mutex.synchronize {
        oldDelay=@writeDela
        @writeDelay=-10000
        checkWriteCache
        @writeDelay=oldDelay
        assert { @dataWriteTime.length==0}
      }
    end
    
    private
    def checkWriteCache
      @dataWriteTime.each{|k,v|
        if v<Time.now-@writeDelay
          # write
          @store[k]=@dataCache[k]
          @dataWriteTime.delete(k)
        end
      }
      
      checkHoldCache
    end
    
    def currentCacheSize
      @dataCache.values.map{|s|s.length}.inject(0){|a,b|a+b}
    end
    
    # should only be called when 
    def checkHoldCache
      while currentCacheSize>@cacheSize
        # remove least recently accessed
        leastTime=@dataAccessTime.values.min
        
        keys=@dataAccessTime.keys.select{|k|@dataAccessTime[k]<=leastTime}
        keys.each{|key|
          unless @dataWriteTime.key?(key)
            removeFromCache(key)
          end
        }
      end
    end
    def removeFromCache(key)
      @dataCache.delete(key)
      @dataAccessTime.delete(key)
      @dataWriteTime.delete(key)
    end
  end
end