# Copyright 2018 Google LLC
#
# Licensed 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
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""An example DAG demonstrating simple Apache Airflow operators."""

# [START composer_simple]
from __future__ import print_function

# [START composer_simple_define_dag]
import datetime

from airflow import models
# [END composer_simple_define_dag]
# [START composer_simple_operators]
from airflow.operators import bash_operator
from airflow.operators import python_operator
# [END composer_simple_operators]


# [START composer_simple_define_dag]
default_dag_args = {
    # The start_date describes when a DAG is valid / can be run. Set this to a
    # fixed point in time rather than dynamically, since it is evaluated every
    # time a DAG is parsed. See:
    # https://airflow.apache.org/faq.html#what-s-the-deal-with-start-date
    'start_date': datetime.datetime(2018, 1, 1),
}

# Define a DAG (directed acyclic graph) of tasks.
# Any task you create within the context manager is automatically added to the
# DAG object.
with models.DAG(
        'composer_sample_simple_greeting',
        schedule_interval=datetime.timedelta(days=1),
        default_args=default_dag_args) as dag:
    # [END composer_simple_define_dag]
    # [START composer_simple_operators]
    def greeting():
        import logging
        logging.info('Hello World!')

    # An instance of an operator is called a task. In this case, the
    # hello_python task calls the "greeting" Python function.
    hello_python = python_operator.PythonOperator(
        task_id='hello',
        python_callable=greeting)

    # Likewise, the goodbye_bash task calls a Bash script.
    goodbye_bash = bash_operator.BashOperator(
        task_id='bye',
        bash_command='echo Goodbye.')
    # [END composer_simple_operators]

    # [START composer_simple_relationships]
    # Define the order in which the tasks complete by using the >> and <<
    # operators. In this example, hello_python executes before goodbye_bash.
    hello_python >> goodbye_bash
    # [END composer_simple_relationships]
# [END composer_simple]