AP-687 Only download files if local file is older

[jason-raitz]

• given a UTC modified datetime string for the requested file, we now check if the file exists locally and has a newer mtime

[awilfox]

r+wc; minor documentation fixes.

[awilfox]

Wouldn't this be a single entry in the changelog?

[awilfox]

Not only for alphabetisation, but because etree is sometimes considered external.

Suggested change

	from io import StringIO
	from pathlib import Path
	from typing import Any, Iterator
	import xml.etree.ElementTree as E
	from datetime import datetime, timezone
	from datetime import datetime, timezone
	from io import StringIO
	from pathlib import Path
	from typing import Any, Iterator
	import xml.etree.ElementTree as E

[awilfox]

Suggested change

	"""Download a file from TIND and save it locally. If the file already exists in the output
	directory and has a local modified timestamp that is newer than supplied ``modified``
	timestamp, the file will not be re-downloaded.
	"""Download a file from TIND and save it locally.
	If the file already exists in the output directory and was modified at or after a supplied ``modified``
	timestamp, the file will not be re-downloaded.

[awilfox]

Suggested change

	:param str modified: Optional modified timestamp from the file metadata returned by TIND
	:param str modified: Optional modified timestamp from the file metadata returned by TIND.
	If not specified, the file will always be downloaded.

[awilfox]

It would be nice to have a test. We should be able to mock stat to return specific dates instead of relying on fixture dates / filesystem stuff.