from __future__ import absolute_import

import random

from .hashed import murmur2


class DefaultPartitioner(object):
    """Default partitioner.

    Hashes key to partition using murmur2 hashing (from java client)
    If key is None, selects partition randomly from available,
    or from all partitions if none are currently available
    """
    @classmethod
    def __call__(cls, key, all_partitions, available):
        if key is None:
            if available:
                return random.choice(available)
            return random.choice(all_partitions)

        idx = murmur2(key)
        idx &= 0x7fffffff
        idx %= len(all_partitions)
        return all_partitions[idx]