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import threading
from typing import TYPE_CHECKING

from elasticapm.context.base import BaseContext

if TYPE_CHECKING:
    import elasticapm.traces


class ThreadLocalContext(BaseContext):
    thread_local = threading.local()
    # TODO why do we getattr on every access if the variables are defined here?
    thread_local.transaction = None
    thread_local.spans = ()

    def get_transaction(self, clear: bool = False) -> "elasticapm.traces.Transaction":
        """
        Get the transaction for the current execution context

        If clear=True, also set the transaction to None for the current
        execution context.
        """
        transaction = getattr(self.thread_local, "transaction", None)
        if clear:
            self.thread_local.transaction = None
        return transaction

    def set_transaction(self, transaction: "elasticapm.traces.Transaction") -> None:
        """
        Set the transaction for the current execution context
        """
        self.thread_local.transaction = transaction

    def get_span(self) -> "elasticapm.traces.Span":
        """
        Get the active span for the current execution context.
        """
        spans = getattr(self.thread_local, "spans", ())
        span = None
        if spans:
            span = spans[-1]
        return span

    def set_span(self, span: "elasticapm.traces.Span") -> None:
        """
        Set the active span for the current execution context.

        The previously-activated span will be saved to be re-activated later.
        """
        self.thread_local.spans = getattr(self.thread_local, "spans", ()) + (span,)

    def unset_span(self, clear_all: bool = False) -> "elasticapm.traces.Span":
        """
        De-activate the current span. If a span was previously active, it will
        become active again.

        Returns the deactivated span.

        If clear_all=True, all spans will be cleared and no span will be active.
        """
        spans = getattr(self.thread_local, "spans", ())
        span = None
        if spans:
            span = spans[-1]
            if clear_all:
                self.thread_local.spans = ()
            else:
                self.thread_local.spans = spans[0:-1]
        return span


execution_context = ThreadLocalContext()