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"""
Example DAG demonstrating a workflow with nested branching. The join tasks are created with
``none_failed_min_one_success`` trigger rule such that they are skipped whenever their corresponding
branching tasks are skipped.
"""
from __future__ import annotations

import pendulum

from airflow.decorators import task
from airflow.models.dag import DAG
from airflow.operators.empty import EmptyOperator
from airflow.utils.trigger_rule import TriggerRule

with DAG(
    dag_id="example_nested_branch_dag",
    start_date=pendulum.datetime(2021, 1, 1, tz="UTC"),
    catchup=False,
    schedule="@daily",
    tags=["example"],
) as dag:

    @task.branch()
    def branch(task_id_to_return: str) -> str:
        return task_id_to_return

    branch_1 = branch.override(task_id="branch_1")(task_id_to_return="true_1")
    join_1 = EmptyOperator(task_id="join_1", trigger_rule=TriggerRule.NONE_FAILED_MIN_ONE_SUCCESS)
    true_1 = EmptyOperator(task_id="true_1")
    false_1 = EmptyOperator(task_id="false_1")

    branch_2 = branch.override(task_id="branch_2")(task_id_to_return="true_2")
    join_2 = EmptyOperator(task_id="join_2", trigger_rule=TriggerRule.NONE_FAILED_MIN_ONE_SUCCESS)
    true_2 = EmptyOperator(task_id="true_2")
    false_2 = EmptyOperator(task_id="false_2")
    false_3 = EmptyOperator(task_id="false_3")

    branch_1 >> true_1 >> join_1
    branch_1 >> false_1 >> branch_2 >> [true_2, false_2] >> join_2 >> false_3 >> join_1