from twisted.internet import defer
from twisted.internet.base import ThreadedResolver

from scrapy.utils.datatypes import LocalCache

# TODO: cache misses
# TODO: make cache size a setting

dnscache = LocalCache(10000)

class CachingThreadedResolver(ThreadedResolver):

    def getHostByName(self, name, timeout = (1, 3, 11, 45)):
        if name in dnscache:
            return defer.succeed(dnscache[name])
        d = ThreadedResolver.getHostByName(self, name, timeout)
        d.addCallback(self._cache_result, name)
        return d

    def _cache_result(self, result, name):
        dnscache[name] = result
        return result