Implement Evaluation Configuration Variables/Expressions

[christophertubbs]

The configuration for an element for an evaluation might look like:

"backend": {
                "backend_type": "rest",
                "data_format": "json",
                "address": "https://nwis.waterservices.usgs.gov/nwis/iv",
                "params": {
                    "format": "json",
                    "indent": "on",
                    "sites": "0214657975,0214655255",
                    "startDT": "2022-12-01T00:00%2b0000",
                    "endDT": "2022-12-31T00:00%2b0000",
                    "parameterCd": "00060"
                }
            }

It would be useful to insert variables so that the same configuration may be used multiple times as conditions and needs change. The above configuration my look like the following with variable functionality:

"backend": {
                "backend_type": "rest",
                "data_format": "json",
                "address": "https://nwis.waterservices.usgs.gov/nwis/iv",
                "params": {
                    "format": "json",
                    "indent": "on",
                    "sites": "0214657975,0214655255",
                    "startDT": "{{ NOW - timedelta(hours=48) }}",
                    "endDT": "{{ NOW }}",
                    "parameterCd": "00060"
                }
            }

Another example could be:

"backend": {
                "backend_type": "file",
                "data_format": "rdb",
                "address": "{{ THRESHOLD_DIRECTORY }}/nwis_stat_thresholds.rdb"
            }

instead of

"backend": {
                "backend_type": "file",
                "data_format": "rdb",
                "address": "path/to/nwis_stat_thresholds.rdb"
            }

Steps:

• Determine Syntax, allowable data types, and allowable operations #686
• Determine constants (such as NOW) #687
• Write Parser #689
• Insert processing step for the parser #690
• Write instructions on how to use evaluation configuration expressions #692
• Write Unit Tests #691

This may be considered as done when a configuration may include strings such as "{{ NOW }} " or " {{ CONSTANT }}/path/to/whatever" may be used, are fully documented, and are have a good deal of unit tests.

[robertbartel]

Marking as Blocked to flag the issue, as I think this may have been completed.

[robertbartel]

FYI @christophertubbs, with this now being broken down nicely into subtasks, I've added the epic tag. That will keep it from being visible where it was previously in the project board, but you can still find it in the BL Multi-Task Issues view.