# -*- 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
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from airflow.models import BaseOperator
from airflow.models.skipmixin import SkipMixin
from airflow.utils import timezone


class LatestOnlyOperator(BaseOperator, SkipMixin):
    """
    Allows a workflow to skip tasks that are not running during the most
    recent schedule interval.

    If the task is run outside of the latest schedule interval, all
    directly downstream tasks will be skipped.
    """

    ui_color = '#e9ffdb'  # nyanza

    def execute(self, context):
        # If the DAG Run is externally triggered, then return without
        # skipping downstream tasks
        if context['dag_run'] and context['dag_run'].external_trigger:
            self.log.info("Externally triggered DAG_Run: allowing execution to proceed.")
            return

        now = timezone.utcnow()
        left_window = context['dag'].following_schedule(
            context['execution_date'])
        right_window = context['dag'].following_schedule(left_window)
        self.log.info(
            'Checking latest only with left_window: %s right_window: %s now: %s',
            left_window, right_window, now
        )

        if not left_window < now <= right_window:
            self.log.info('Not latest execution, skipping downstream.')

            downstream_tasks = context['task'].get_flat_relatives(upstream=False)
            self.log.debug("Downstream task_ids %s", downstream_tasks)

            if downstream_tasks:
                self.skip(context['dag_run'],
                          context['ti'].execution_date,
                          downstream_tasks)

            self.log.info('Done.')
        else:
            self.log.info('Latest, allowing execution to proceed.')
