import random

from .abc import Partitioner


class DefaultPartitioner(Partitioner):
    """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
    """
    def partition(self, topic, key, serialized_key, value, serialized_value, cluster):
        if topic not in cluster.topics():
            raise ValueError("Topic %s not found in ClusterMetadata" % (topic,))
        all_partitions = sorted(cluster.partitions_for_topic(topic))
        available = list(cluster.available_partitions_for_topic(topic))
        if serialized_key is not None:
            idx = murmur2(serialized_key)
            idx &= 0x7fffffff
            idx %= len(all_partitions)
            return all_partitions[idx]
        pool = available if available else all_partitions
        return random.choice(pool)


# https://github.com/apache/kafka/blob/0.8.2/clients/src/main/java/org/apache/kafka/common/utils/Utils.java#L244
def murmur2(data):
    """Pure-python Murmur2 implementation.

    Based on java client, see org.apache.kafka.common.utils.Utils.murmur2

    Args:
        data (bytes): opaque bytes

    Returns: MurmurHash2 of data
    """
    length = len(data)
    seed = 0x9747b28c
    # 'm' and 'r' are mixing constants generated offline.
    # They're not really 'magic', they just happen to work well.
    m = 0x5bd1e995
    r = 24

    # Initialize the hash to a random value
    h = seed ^ length
    length4 = length // 4

    for i in range(length4):
        i4 = i * 4
        k = ((data[i4 + 0] & 0xff) +
            ((data[i4 + 1] & 0xff) << 8) +
            ((data[i4 + 2] & 0xff) << 16) +
            ((data[i4 + 3] & 0xff) << 24))
        k &= 0xffffffff
        k *= m
        k &= 0xffffffff
        k ^= (k % 0x100000000) >> r # k ^= k >>> r
        k &= 0xffffffff
        k *= m
        k &= 0xffffffff

        h *= m
        h &= 0xffffffff
        h ^= k
        h &= 0xffffffff

    # Handle the last few bytes of the input array
    extra_bytes = length % 4
    if extra_bytes >= 3:
        h ^= (data[(length & ~3) + 2] & 0xff) << 16
        h &= 0xffffffff
    if extra_bytes >= 2:
        h ^= (data[(length & ~3) + 1] & 0xff) << 8
        h &= 0xffffffff
    if extra_bytes >= 1:
        h ^= (data[length & ~3] & 0xff)
        h &= 0xffffffff
        h *= m
        h &= 0xffffffff

    h ^= (h % 0x100000000) >> 13 # h >>> 13;
    h &= 0xffffffff
    h *= m
    h &= 0xffffffff
    h ^= (h % 0x100000000) >> 15 # h >>> 15;
    h &= 0xffffffff

    return h