# Copyright 2021 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

#

# http://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.

#

"""Helper functions to convert ISO 8601 strings into datetime objects.

"""

import datetime

import re

def iso8601_datetime_utc(utc_date_time: str) -> datetime.datetime:

"""Converts an ISO 8601 string ("yyyy-mm-ddThh:mm:ssZ") to a datetime object.

More details: https://en.wikipedia.org/wiki/ISO_8601

Args:

utc_date_time: Date and time in the extended ("T") ISO 8601 format, where

the time is in UTC ("Z").

Returns:

Builtin datetime object with a UTC timezone.

Raises:

ValueError: Invalid input value.

"""

# Work-around fixable issues in user-specified timestamps.

utc_date_time = re.sub(r"(\d{2}-\d{2}-\d{2})\s+(\d)", r"\1T\2",

utc_date_time).upper()

if utc_date_time[-1] != "Z":

utc_date_time += "Z"

# Append the suffix "+0000" in order to produce a timezone-aware UTC datetime,

# because strptime's "%z" does not recognize the meaning of the "Z" suffix.

try:

# Support (but don't require) sub-second parsing, but ignore anything

# smaller than microseconds.

utc_date_time = re.sub(r"(\d{6})\d+Z", r"\1Z", utc_date_time)

return datetime.datetime.strptime(f"{utc_date_time}+0000",

"%Y-%m-%dT%H:%M:%S.%fZ%z")

except ValueError:

# No microseconds? No problem, try to parse without them.

# If there's a different parsing problem, it will surface below too.

pass

return datetime.datetime.strptime(f"{utc_date_time}+0000",

"%Y-%m-%dT%H:%M:%SZ%z")

def strftime(utc_date_time: datetime.datetime) -> str:

"""Converts a datetime object to a string with the format "%Y-%m-%dT%H:%M:%SZ".

Args:

utc_date_time: Builtin datetime object with a UTC timezone.

Returns:

Date and time in the format "%Y-%m-%dT%H:%M:%SZ".

Raises:

ValueError: Invalid input value.

"""

if utc_date_time is None:

return ""

return utc_date_time.astimezone(

datetime.timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")