Add more complex parameter validation

[crepe]

Add more complex parameter validation

[krainboltgreene]

So just to throw in my two cents implementation:

This is what I end up doing:

class Accounts < Crepe::API
  puts do
    Account::Control::Create.new(payload: Account::Normalizer::Create.new(params))
  end
end

If I had to do a DSL this I might want to do:

class Accounts < Crepe::API
  get do
    parameters require: "account"
    parameters allow: ["account", "name"]
    parameters allow: ["account", "email"]
  end
end

[stephencelis]

@krainboltgreene I think the current interface works well for your example, though it's more imperative and less declarative. Where parameter validation could functionally improve is:

1. provide validation beyond required/allowed parameters and
2. bring it outside the scope of the individual endpoint (so that it gets evaluated before an endpoint itself is called)

The first point allows for things like type/minimum/maximum/inclusive/exclusive/pattern validations.
The second point allows for introspection, which would be crucial to give Crepe (or rather a plugin, crepe-doc) the ability to generate extensive documentation for an API.

[kainosnoema]

Is there any existing, maintained and extensible framework for generic validations that we could base our validations off of? I don't mind building this ourselves if we need to, but validations can be tricky, and I bet something like this exists that we could build from.