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# COPYRIGHT(c) 2018 STMicroelectronics                                         #
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# IMPORT

from blue_st_sdk.feature import Feature


# CLASSES

class DeviceTimestampFeature(Feature):
    """Class that a feature has to extend if it doesn't have the timestamp field.
    The system time is used as timestamp.

    Refer to
    `Heart Rate Measurement Specs <https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.heart_rate_measurement.xml>`_
    for more information.
    """

    def __init__(self, name, node, description):
        """Constructor.
        
        Args:
            name (str): Name of the feature.
            node (:class:`blue_st_sdk.node.Node`): Node that will update the
                feature.
            description (str): Description of the data of the feature.
        """
        super(DeviceTimestampFeature, self).__init__(name, node, description)

    def _update(self, timestamp, data, offset):
        """Change the timestamp with the system timestamp and reset the data
        offset.
    
        Args:
            timestamp (int): Package timestamp.
            data (list): Array of data.
            offset (int): Offset position to start reading data.
        
        Returns:
            The number of bytes read.
        """
        return super(DeviceTimestampFeature, self)._update(datetime.now(), data, offset - 2)
