# -*- coding: utf-8 -*-
#
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# to you 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
#
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import random

from airflow.models import DAG
from airflow.operators.dummy_operator import DummyOperator
from airflow.operators.python_operator import BranchPythonOperator
from airflow.utils.dates import days_ago

args = {
    'owner': 'Airflow',
    'start_date': days_ago(2),
}

dag = DAG(
    dag_id='example_branch_operator',
    default_args=args,
    schedule_interval="@daily",
    tags=['example']
)

run_this_first = DummyOperator(
    task_id='run_this_first',
    dag=dag,
)

options = ['branch_a', 'branch_b', 'branch_c', 'branch_d']

branching = BranchPythonOperator(
    task_id='branching',
    python_callable=lambda: random.choice(options),
    dag=dag,
)
run_this_first >> branching

join = DummyOperator(
    task_id='join',
    trigger_rule='none_failed_or_skipped',
    dag=dag,
)

for option in options:
    t = DummyOperator(
        task_id=option,
        dag=dag,
    )

    dummy_follow = DummyOperator(
        task_id='follow_' + option,
        dag=dag,
    )

    branching >> t >> dummy_follow >> join
