#!/usr/bin/env python
# Copyright (c) 2016 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Writes a file that contains a define that approximates the build date.

build_type impacts the timestamp generated:
- default: the build date is set to the most recent first Sunday of a month at
  5:00am. The reason is that it is a time where invalidating the build cache
  shouldn't have major repercussions (due to lower load).
- official: the build date is set to the current date at 5:00am, or the day
  before if the current time is before 5:00am.
Either way, it is guaranteed to be in the past and always in UTC.

It is also possible to explicitly set a build date to be used.
"""

import argparse
import calendar
import datetime
import doctest
import os
import sys


THIS_DIR = os.path.abspath(os.path.dirname(__file__))


def GetFirstSundayOfMonth(year, month):
  """Returns the first sunday of the given month of the given year.

  >>> GetFirstSundayOfMonth(2016, 2)
  7
  >>> GetFirstSundayOfMonth(2016, 3)
  6
  >>> GetFirstSundayOfMonth(2000, 1)
  2
  """
  weeks = calendar.Calendar().monthdays2calendar(year, month)
  # Return the first day in the first week that is a Sunday.
  return [date_day[0] for date_day in weeks[0] if date_day[1] == 6][0]


def GetBuildDate(build_type, utc_now):
  """Gets the approximate build date given the specific build type.

  >>> GetBuildDate('default', datetime.datetime(2016, 2, 6, 1, 2, 3))
  'Jan 03 2016 01:02:03'
  >>> GetBuildDate('default', datetime.datetime(2016, 2, 7, 5))
  'Feb 07 2016 05:00:00'
  >>> GetBuildDate('default', datetime.datetime(2016, 2, 8, 5))
  'Feb 07 2016 05:00:00'
  """
  day = utc_now.day
  month = utc_now.month
  year = utc_now.year
  if build_type != 'official':
    first_sunday = GetFirstSundayOfMonth(year, month)
    # If our build is after the first Sunday, we've already refreshed our build
    # cache on a quiet day, so just use that day.
    # Otherwise, take the first Sunday of the previous month.
    if day >= first_sunday:
      day = first_sunday
    else:
      month -= 1
      if month == 0:
        month = 12
        year -= 1
      day = GetFirstSundayOfMonth(year, month)
  now = datetime.datetime(
      year, month, day, utc_now.hour, utc_now.minute, utc_now.second)
  return '{:%b %d %Y %H:%M:%S}'.format(now)


def main():
  if doctest.testmod()[0]:
    return 1
  argument_parser = argparse.ArgumentParser(
      description=sys.modules[__name__].__doc__,
      formatter_class=argparse.RawDescriptionHelpFormatter)
  argument_parser.add_argument('output_file', help='The file to write to')
  argument_parser.add_argument(
      'build_type', help='The type of build', choices=('official', 'default'))
  args = argument_parser.parse_args()

  # The mtime of the revision in build/util/LASTCHANGE is stored in a file
  # next to it. Read it, to get a deterministic time close to "now".
  # That date is then modified as described at the top of the file so that
  # it changes less frequently than with every commit.
  # This intentionally always uses build/util/LASTCHANGE's commit time even if
  # use_dummy_lastchange is set.
  lastchange_file = os.path.join(THIS_DIR, 'util', 'LASTCHANGE.committime')
  last_commit_timestamp = int(open(lastchange_file).read())
  now = datetime.datetime.utcfromtimestamp(last_commit_timestamp)

  if now.hour < 5:
    # The time is locked at 5:00 am in UTC to cause the build cache
    # invalidation to not happen exactly at midnight. Use the same calculation
    # as the day before.
    # See //base/build_time.cc.
    now = now - datetime.timedelta(days=1)
  now = datetime.datetime(now.year, now.month, now.day, 5, 0, 0)
  build_date = GetBuildDate(args.build_type, now)

  output = ('// Generated by //build/write_build_date_header.py\n'
           '#ifndef BUILD_DATE\n'
           '#define BUILD_DATE "{}"\n'
           '#endif // BUILD_DATE\n'.format(build_date))

  current_contents = ''
  if os.path.isfile(args.output_file):
    with open(args.output_file, 'r') as current_file:
      current_contents = current_file.read()

  if current_contents != output:
    with open(args.output_file, 'w') as output_file:
      output_file.write(output)
  return 0


if __name__ == '__main__':
  sys.exit(main())