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from airflow.ti_deps.deps.base_ti_dep import BaseTIDep
from airflow.utils.session import provide_session


class DagTISlotsAvailableDep(BaseTIDep):
    """Determines whether a DAG maximum number of running tasks has been reached."""

    NAME = "Task Instance Slots Available"
    IGNORABLE = True

    @provide_session
    def _get_dep_statuses(self, ti, session, dep_context):
        if ti.task.dag.get_concurrency_reached(session):
            yield self._failing_status(
                reason="The maximum number of running tasks ({}) for this task's DAG "
                "'{}' has been reached.".format(ti.task.dag.max_active_tasks, ti.dag_id)
            )