# -*- coding: utf-8 -*-
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from airflow.ti_deps.deps.base_ti_dep import BaseTIDep
from airflow.utils.db import provide_session
from airflow.utils.state import State


class NotRunningDep(BaseTIDep):
    NAME = "Task Instance Not Already Running"

    # Task instances must not already be running, as running two copies of the same
    # task instance at the same time (AKA double-trigger) should be avoided at all
    # costs, even if the context specifies that all dependencies should be ignored.
    IGNOREABLE = False

    @provide_session
    def _get_dep_statuses(self, ti, session, dep_context):
        if ti.state == State.RUNNING:
            yield self._failing_status(
                reason="Task is already running, it started on {0}.".format(
                    ti.start_date))
