#!/usr/bin/env python

# Copyright 2014 IIJ Innovation Institute Inc. All rights reserved.
# Copyright 2014 Keiichi Shima. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
#       copyright notice, this list of conditions and the following
#       disclaimer in the documentation and/or other materials provided
#       with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
# ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
# GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
# OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF

import time

class SensorBase(object):
    def __init__(self, update_callback):
        assert (update_callback is not None)

        self._cache_lifetime = 0
        self._last_updated = None
        self._update_callback = update_callback

    def _update(self, **kwargs):
        now = time.time()

        # If caching is disabled, just update the data.
        if self._cache_lifetime > 0:
            # Check if the cached value is still valid or not.
            if (self._last_updated is not None
                and self._last_updated + self._cache_lifetime > now):
                # The value is still valid.
                return

        # Get the latest sensor values.
        self._update_callback(**kwargs)
        self._last_updated = now

        return

    @property
    def cache_lifetime(self):
        '''Gets/Sets the cache time (in seconds).

        '''
        return (self._cache_lifetime)

    @cache_lifetime.setter
    def cache_lifetime(self, cache_lifetime):
        assert(cache_lifetime >= 0)

        self._cache_lifetime = cache_lifetime
