There is no concept of ‘current survey’ in Dougal, and
assigning navigation data to a particular survey is full
of edge cases but sometimes it is necessary or at least
convenient to do so.
This commit implements once such strategy, which consists
of checking the distance to the preplots of all active
surveys (well, those that do have preplots anyway) and
picking the nearest one.
To reduce load, we only do this every once in a while as
governed by the `offline_survey_detect_interval` option
in the configuration.
This strategy is only active if the configuration option
`offline_survey_heuristics == "nearest_preplot"` for the
corresponding navigation header.
We now check that a file is at least a few seconds old
before attempting to import it.
The actual minimum age can be configured in etc/config.yaml or
else is defaults to 10 seconds.
The idea is that this should give the OS enough time to fully
write the file before we import it.
The timestamp being looked at is the modification time.
Fixes#92.
In case of errors (or anything else of note), send_alert.py
can be used to push information to a GitLab alerts endpoint.
It is generic enough that it can be used with anything else, though.
