Generate the context for a Cookiecutter project template.

    Loads the JSON file as a Python object, with key being the JSON filename.

    :param context_file: JSON file containing key/value pairs for populating
        the cookiecutter's variables.
    :param default_context: Dictionary containing config to take into account.
    :param extra_context: Dictionary containing configuration overrides

def generate_context(context_file='cookiecutter.json', default_context=None,
                     extra_context=None):
    """Generate the context for a Cookiecutter project template.

    Loads the JSON file as a Python object, with key being the JSON filename.

    :param context_file: JSON file containing key/value pairs for populating
        the cookiecutter's variables.
    :param default_context: Dictionary containing config to take into account.
    :param extra_context: Dictionary containing configuration overrides
    """
    context = OrderedDict([])

    try:
        with open(context_file) as file_handle:
            obj = json.load(file_handle, object_pairs_hook=OrderedDict)
    except ValueError as e:
        # JSON decoding error.  Let's throw a new exception that is more
        # friendly for the developer or user.
        full_fpath = os.path.abspath(context_file)
        json_exc_message = str(e)
        our_exc_message = (
            'JSON decoding error while loading "{0}".  Decoding'
            ' error details: "{1}"'.format(full_fpath, json_exc_message))
        raise ContextDecodingException(our_exc_message)

    # Add the Python object to the context dictionary
    file_name = os.path.split(context_file)[1]
    file_stem = file_name.split('.')[0]
    context[file_stem] = obj

    # Overwrite context variable defaults with the default context from the
    # user's global config, if available
    if default_context:
        apply_overwrites_to_context(obj, default_context)
    if extra_context:
        apply_overwrites_to_context(obj, extra_context)

    logger.debug('Context generated is {}'.format(context))
    return context