Determine constants (such as NOW)

[christophertubbs]

Environment and application constants should be integrated into the parsing process to allow for configuration reuse. To do that, the constants should first be determined. These constants should be things that indicate common relative values such as directory paths and dates. NOW should absolutely be included.

All initial constants need to be determined and mapped to their meanings like so:

• NOW: datetime.now().astimezone()

It might also be worth determining if these 'constants' need to be configurable. For instance, if there are supposed to be constants for common paths, like THRESHOLD_DIRECTORY pointing at a directory for common thresholds, allow those values to be configured in a separate file/format to allow paths to be added and removed without redeployment.

The ORM for the evaluation service would be fantastic for this as it can attach descriptions to the paths and the constants and the descriptions may be queried for further functionality elsewhere. The challenge there, though, would be that the processing happens in dmod.evaluations, not within the evaluation service, so some form of dependency injection will be required.