Add Trigger condition parser and resolver for Doc Level Alerts

[getsaurabh02]

Add Trigger condition parser which parses the provided trigger condition expression in the Reverse Polish Notation and then
resolves the final set of Document Ids which matches the given expression for Document Level Alerts.

Users can configure the Trigger condition using the expression strings as below:

Always True
return true

Always False
return false

Query Expressions

* (query[name=sigma-123] && query[name=sigma-456]) || (!query[id=aert34df] && query[tag=sev2])
* query[tag=sev1]
* (query[name=sigma-123] && query[tag=sev2]) || (!query[tag=sev3] && query[id=dfd457iy] && query[tag=“sev1"])

Operartors supported are:

* (
* )
* &&
* ||
* !

Query Identifiers supported are:

* name ---> query[name=sigma-123]
* tag ---> query[tag=sev2]
* id ---> query[id=aert34df]

Signed-off-by: Saurabh Singh [email protected]

Issue #, if available:

Description of changes:

CheckList:
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[sbcd90]

the if-else if block moves the object equals check to runtime. Kotlin allows this check to be made at compile time using when control statements.

when (trigger.condition.idOrCode) {
                ALWAYS_RUN.idOrCode  -> {
                    for (value in queryToDocIds.values) {
                        triggeredDocs.addAll(value)
                    }
                }
                NEVER_RUN.idOrCode -> {
                    triggeredDocs = TriggerExpressionParser(trigger.condition.idOrCode).parse()
                        .evaluate(queryToDocIds).toMutableList()
                }
            }

this will allow catching runtime errors we faced today at compile time only.

[getsaurabh02]

Thanks for the suggestion @sbcd90. Agree, control statement could make the flow look much cleaner and I have used it in the Parser/Evaluation logic. However, here since this is not an instance check, but rather the value check with string comparison, I am not sure having control statement would add any value here in terms of performance. Given string value comparison still need to be performed at runtime.

Since we weren't using all the three possible values here, I chose to keep it as if-else block instead.

[sbcd90]

should the class name be changed to TriggerRPNExpressionParser?
parse() returns TriggerExpressionRPNResolver
tomorrow if someone wants to have another implementation of interface ExpressionParser

[getsaurabh02]

Since currently there is only one concrete implementation of the Trigger Expression Parser have kept the name as is for clarity. However, the base implementation which holds the RPN logic is named as the TriggerExpressionRPNBaseParser.
Later addition of new base implementations are possible using the new strategy, while the concrete implementation could still expose them via different method interfaces.