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# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
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#    http://www.apache.org/licenses/LICENSE-2.0
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"""A streaming word-counting workflow.

Important: streaming pipeline support in Python Dataflow is in development
and is not yet available for use.
"""

from __future__ import absolute_import

import argparse
import logging

from past.builtins import unicode

import apache_beam as beam
import apache_beam.transforms.window as window

TABLE_SCHEMA = ('word:STRING, count:INTEGER, '
                'window_start:TIMESTAMP, window_end:TIMESTAMP')


def find_words(element):
  import re
  return re.findall(r'[A-Za-z\']+', element)


class FormatDoFn(beam.DoFn):
  def process(self, element, window=beam.DoFn.WindowParam):
    ts_format = '%Y-%m-%d %H:%M:%S.%f UTC'
    window_start = window.start.to_utc_datetime().strftime(ts_format)
    window_end = window.end.to_utc_datetime().strftime(ts_format)
    return [{'word': element[0],
             'count': element[1],
             'window_start':window_start,
             'window_end':window_end}]


def run(argv=None):
  """Build and run the pipeline."""

  parser = argparse.ArgumentParser()
  parser.add_argument(
      '--input_topic', required=True,
      help='Input PubSub topic of the form "/topics/<PROJECT>/<TOPIC>".')
  parser.add_argument(
      '--output_table', required=True,
      help=
      ('Output BigQuery table for results specified as: PROJECT:DATASET.TABLE '
       'or DATASET.TABLE.'))
  known_args, pipeline_args = parser.parse_known_args(argv)

  with beam.Pipeline(argv=pipeline_args) as p:

    # Read the text from PubSub messages.
    lines = p | beam.io.ReadFromPubSub(known_args.input_topic)

    # Get the number of appearances of a word.
    def count_ones(word_ones):
      (word, ones) = word_ones
      return (word, sum(ones))

    transformed = (lines
                   | 'Split' >> (beam.FlatMap(find_words)
                                 .with_output_types(unicode))
                   | 'PairWithOne' >> beam.Map(lambda x: (x, 1))
                   | beam.WindowInto(window.FixedWindows(2*60, 0))
                   | 'Group' >> beam.GroupByKey()
                   | 'Count' >> beam.Map(count_ones)
                   | 'Format' >> beam.ParDo(FormatDoFn()))

    # Write to BigQuery.
    # pylint: disable=expression-not-assigned
    transformed | 'Write' >> beam.io.WriteToBigQuery(
        known_args.output_table,
        schema=TABLE_SCHEMA,
        create_disposition=beam.io.BigQueryDisposition.CREATE_IF_NEEDED,
        write_disposition=beam.io.BigQueryDisposition.WRITE_APPEND)


if __name__ == '__main__':
  logging.getLogger().setLevel(logging.INFO)
  run()