# Source code for opentelemetry.sdk.metrics._internal.exemplar.exemplar_filter

    # Copyright The OpenTelemetry Authors
    #
    # 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.

    from abc import ABC, abstractmethod
    from typing import Union

    from opentelemetry import trace
    from opentelemetry.context import Context
    from opentelemetry.trace.span import INVALID_SPAN
    from opentelemetry.util.types import Attributes

    class ExemplarFilter(ABC):
        """``ExemplarFilter`` determines which measurements are eligible for becoming an
        ``Exemplar``.

        Exemplar filters are used to filter measurements before attempting to store them
        in a reservoir.

        Reference:
            https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#exemplarfilter
        """

        @abstractmethod
        def should_sample(
            self,
            value: Union[int, float],
            time_unix_nano: int,
            attributes: Attributes,
            context: Context,
        ) -> bool:
            """Returns whether or not a reservoir should attempt to filter a measurement.

            Args:
                value: The value of the measurement
                timestamp: A timestamp that best represents when the measurement was taken
                attributes: The complete set of measurement attributes
                context: The Context of the measurement
            """
            raise NotImplementedError(
                "ExemplarFilter.should_sample is not implemented"
            )

    class AlwaysOnExemplarFilter(ExemplarFilter):
        """An ExemplarFilter which makes all measurements eligible for being an Exemplar.

        Reference:
            https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#alwayson
        """

        def should_sample(
            self,
            value: Union[int, float],
            time_unix_nano: int,
            attributes: Attributes,
            context: Context,
        ) -> bool:
            """Returns whether or not a reservoir should attempt to filter a measurement.

            Args:
                value: The value of the measurement
                timestamp: A timestamp that best represents when the measurement was taken
                attributes: The complete set of measurement attributes
                context: The Context of the measurement
            """
            return True

    class AlwaysOffExemplarFilter(ExemplarFilter):
        """An ExemplarFilter which makes no measurements eligible for being an Exemplar.

        Using this ExemplarFilter is as good as disabling Exemplar feature.

        Reference:
            https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#alwaysoff
        """

        def should_sample(
            self,
            value: Union[int, float],
            time_unix_nano: int,
            attributes: Attributes,
            context: Context,
        ) -> bool:
            """Returns whether or not a reservoir should attempt to filter a measurement.

            Args:
                value: The value of the measurement
                timestamp: A timestamp that best represents when the measurement was taken
                attributes: The complete set of measurement attributes
                context: The Context of the measurement
            """
            return False

    class TraceBasedExemplarFilter(ExemplarFilter):
        """An ExemplarFilter which makes those measurements eligible for being an Exemplar,
        which are recorded in the context of a sampled parent span.

        Reference:
            https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#tracebased
        """

        def should_sample(
            self,
            value: Union[int, float],
            time_unix_nano: int,
            attributes: Attributes,
            context: Context,
        ) -> bool:
            """Returns whether or not a reservoir should attempt to filter a measurement.

            Args:
                value: The value of the measurement
                timestamp: A timestamp that best represents when the measurement was taken
                attributes: The complete set of measurement attributes
                context: The Context of the measurement
            """
            span = trace.get_current_span(context)
            if span == INVALID_SPAN:
                return False
            return span.get_span_context().trace_flags.sampled