Path resolver

[CacheControl]

adds path resolver engine option. This allows path syntax other than the json-path default. It also replaces the current selectn built-in fallback with a long term supported solution via the pathResolver callback. Fixes #210 and #187.

[naveen-shetty]

Woohh!! I like this change. I was thinking of something like this last week.

Not that I was looking to use something other than json-path but to overcome this json-path/JsonPath#272 limitation of JSON Path as it is not part of the json-path spec.

The data is my use case looks like something like this. (Yes, ideally this should be a key value pair :()

So, if I want to extract a language name for a given language code, json-path cannot really do that out of the box as it always returns an array of values while dealing with arrays.

var langs = [
  { 
    langucode: 'en',
    name: 'english' 
  },
  { 
   code: 'es',
    name: 'spanish' 
  }, 
  ....
  .....
]

Still not sure if I am going to use it but It does open up the possibility of some custom parsing.

[naveen-shetty]

Do you think it makes sense pass to params as well ? Just in case, some custom pathResolver need details from params.

Suggested change

	const pathValue = this.pathResolver(factValue, path)
	const pathValue = this.pathResolver(factValue, path, params)

[CacheControl]

oh! That's an interesting idea and I see where you're coming from - this could allow a user to configure their path resolve library differently on a condition by condition basis. 🤔

My immediate thinking is that we don't want to mix the concept of fact parameters with path resolver parameters - as things stand right now there would be unintended consequences to things like fact caching, which uses params for fact idempotency. That said, we could easily avoid that issue with a pathParams property.

For now, I think I'd like to see if this request actually materializes in the wild before I add it, and then it can be introduced as a minor version. But cool idea.