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# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# Copyright 2011 Justin Santa Barbara
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

"""Utilities and helper functions."""


import os


def read_cached_file(filename, cache_info, reload_func=None):
    """Read from a file if it has been modified.

    :param cache_info: dictionary to hold opaque cache.
    :param reload_func: optional function to be called with data when
                        file is reloaded due to a modification.

    :returns: data from file

    """
    mtime = os.path.getmtime(filename)
    if not cache_info or mtime != cache_info.get('mtime'):
        with open(filename) as fap:
            cache_info['data'] = fap.read()
        cache_info['mtime'] = mtime
        if reload_func:
            reload_func(cache_info['data'])
    return cache_info['data']


def recursive_keypairs(d):
    """Generator that produces sequence of keypairs for nested dictionaries.
    """
    for name, value in sorted(d.iteritems()):
        if isinstance(value, dict):
            for subname, subvalue in recursive_keypairs(value):
                yield ('%s:%s' % (name, subname), subvalue)
        elif isinstance(value, (tuple, list)):
            # When doing a pair of JSON encode/decode operations to the tuple,
            # the tuple would become list. So we have to generate the value as
            # list here.
            yield name, list(map(lambda x: unicode(x).encode('utf-8'),
                                 value))
        else:
            yield name, value