#!/usr/bin/env python3
# Copyright 2018 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Returns a timestamp that approximates the build date.

build_type impacts the timestamp generated, both relative to the date of the
last recent commit:
- 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 time of the most recent commit.
Either way, it is guaranteed to be in the past and always in UTC.
"""

# The requirements for the timestamp:
# (1) for the purposes of continuous integration, longer duration
#     between cache invalidation is better, but >=1mo is preferable.
# (2) for security purposes, timebombs would ideally be as close to
#     the actual time of the build as possible. It must be in the past.
# (3) HSTS certificate pinning is valid for 70 days. To make CI builds enforce
#     HTST pinning, <=1mo is preferable.
#
# On Windows, the timestamp is also written in the PE/COFF file header of
# executables of dlls.  That timestamp and the executable's file size are
# the only two pieces of information that identify a given executable on
# the symbol server, so rarely changing timestamps can cause conflicts there
# as well. We only upload symbols for official builds to the symbol server.

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 GetUnofficialBuildDate(build_date):
    """Gets the approximate build date given the specific build type.

    >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 6, 1, 2, 3))
    datetime.datetime(2016, 1, 3, 5, 0)
    >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 7, 5))
    datetime.datetime(2016, 2, 7, 5, 0)
    >>> GetUnofficialBuildDate(datetime.datetime(2016, 2, 8, 5))
    datetime.datetime(2016, 2, 7, 5, 0)
    """

    if build_date.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.
        build_date = build_date - datetime.timedelta(days=1)
    build_date = datetime.datetime(
        build_date.year, build_date.month, build_date.day, 5, 0, 0
    )

    day = build_date.day
    month = build_date.month
    year = build_date.year
    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)
    return datetime.datetime(
        year, month, day, build_date.hour, build_date.minute, build_date.second
    )


def main():
    if doctest.testmod()[0]:
        return 1
    argument_parser = argparse.ArgumentParser()
    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())
    build_date = datetime.datetime.fromtimestamp(
        last_commit_timestamp, datetime.timezone.utc
    )

    # For official builds we want full fidelity time stamps because official
    # builds are typically added to symbol servers and Windows symbol servers
    # use the link timestamp as the prime differentiator, but for unofficial
    # builds we do lots of quantization to avoid churn.
    offset = 0
    if args.build_type == 'official':
        if os.name == 'nt':
            version_path = os.path.join(
                THIS_DIR, os.pardir, 'chrome', 'VERSION'
            )
            with open(version_path) as f:
                patch_line = f.readlines()[3].strip()
                # Use the patch number as an offset to the build date so that multiple
                # versions with different patch numbers built from the same source code
                # will get different build_date values. This is critical for Windows
                # symbol servers, to avoid collisions.
                assert patch_line.startswith('PATCH=')
                offset = int(patch_line[6:])
    else:
        build_date = GetUnofficialBuildDate(build_date)
    print(offset + int(calendar.timegm(build_date.utctimetuple())))
    return 0


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