# Authors: see git history
#
# Copyright (c) 2010 Authors
# Licensed under the GNU GPL version 3.0 or later.  See the file LICENSE for details.
import os
import atexit
import hashlib
import pickle

import appdirs
import diskcache

try:
    from functools import lru_cache
except ImportError:
    from backports.functools_lru_cache import lru_cache


# simplify use of lru_cache decorator
def cache(*args, **kwargs):
    return lru_cache(maxsize=None)(*args, **kwargs)


__stitch_plan_cache = None


def get_stitch_plan_cache():
    global __stitch_plan_cache

    if __stitch_plan_cache is None:
        cache_dir = os.path.join(appdirs.user_config_dir('inkstitch'), 'cache', 'stitch_plan')
        __stitch_plan_cache = diskcache.Cache(cache_dir, size=1024 * 1024 * 100)
        atexit.register(__stitch_plan_cache.close)

    return __stitch_plan_cache


class CacheKeyGenerator(object):
    """Generate cache keys given arbitrary data.

    Given arbitrary data, generate short cache key that is extremely likely
    to be unique.

    Use example:

        >>> generator = CacheKeyGenerator()
        >>> generator.update(b'12345')
        >>> generator.update([1, 2, 3, {4, 5, 6}])
        >>> generator.get_cache_key()
    """

    def __init__(self):
        # SHA1 is chosen for speed.  We don't need cryptography-grade hashing
        # for this use case.
        self._hasher = hashlib.sha1()

    def update(self, data):
        """Provide data to be hashed into a cache key.

        Arguments:
            data -- a bytes object or any object that can be pickled
        """

        if not isinstance(data, bytes):
            data = pickle.dumps(data)

        self._hasher.update(data)

    def get_cache_key(self):
        return self._hasher.hexdigest()