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class FailureMap(object):
    def __init__(self):
        self._failures = []

    def add_regression_window(self, builder, regression_window):
        self._failures.append({
            'builder': builder,
            'regression_window': regression_window,
        })

    def is_empty(self):
        return not self._failures

    def failing_revisions(self):
        failing_revisions = [failure_info['regression_window'].revisions()
                             for failure_info in self._failures]
        return sorted(set(sum(failing_revisions, [])))

    def builders_failing_for(self, revision):
        return self._builders_failing_because_of([revision])

    def tests_failing_for(self, revision):
        tests = [failure_info['regression_window'].failing_tests()
                 for failure_info in self._failures
                 if revision in failure_info['regression_window'].revisions()
                    and failure_info['regression_window'].failing_tests()]
        result = set()
        for test in tests:
            result = result.union(test)
        return sorted(result)

    def _old_failures(self, is_old_failure):
        return filter(lambda revision: is_old_failure(revision),
                      self.failing_revisions())

    def _builders_failing_because_of(self, revisions):
        revision_set = set(revisions)
        return [failure_info['builder'] for failure_info in self._failures
                if revision_set.intersection(
                    failure_info['regression_window'].revisions())]

    # FIXME: We should re-process old failures after some time delay.
    # https://bugs.webkit.org/show_bug.cgi?id=36581
    def filter_out_old_failures(self, is_old_failure):
        old_failures = self._old_failures(is_old_failure)
        old_failing_builder_names = set([builder.name()
            for builder in self._builders_failing_because_of(old_failures)])

        # We filter out all the failing builders that could have been caused
        # by old_failures.  We could miss some new failures this way, but
        # emperically, this reduces the amount of spam we generate.
        failures = self._failures
        self._failures = [failure_info for failure_info in failures
            if failure_info['builder'].name() not in old_failing_builder_names]
        self._cache = {}