Sketch of Figgy Pudding Options Processor

figgy-pudding.js

// Requirements:
// Unidirectional (data flows down)
// Composable (detailed definitions can be specified at a lower level)
// Declarative types and defaults
// Minimal consing
// No bubbling of side effects to parents or siblings
// Efficient
// Warn about unspecified options being read or assigned? (or make it available to run in tests?)
// opts objects readable like plain objects (maybe?)

// Example:
const CacacheOpts = figgyPudding({
  cache: {
    type: String
  },
  log: {
    default: require('npmlog')
  }
})

const RegistryClientOpts = figgyPudding({
  retry: {
    // TODO - how should *nested* (vs derived) opts work?
    type: RetryOpts
  },
  log: {
    default: require('npmlog')
  }
}).deriving(RequestOpts)

const PacoteOpts = figgyPudding({
  log: {
    default: require('npmlog')
  },
  where: {
    type: Path,
    default: './'
  }
})
// Deriving:
// * allows reading of same-name parent opts
// * allows passed-in opts to be parsed even though parent doesn't handle them
// * parent cannot read/write child-defined opts it does not share
// * will throw validation errors from children on *initial* instantiation (not on child instantiation)
.deriving(CacacheOpts)
.deriving(RegistryClientOpts)

let myOpts = {
  cache: './cache',
  log: require('./silent-log'),
  auth: auth
}

myFn(1, 2, myOpts)

function myFn (arg1, arg2, _opts) {
  let opts = PacoteOpts(_opts)
  let cacOpts = CacacheOpts(opts) // defaults only processed at this level, and only affect this one
  let regOpts = RegistryClientOpts(opts) // defaults for same name can be different
  
  cacOpts.cache // => './cache'
  cacOpts.log.silly('lol', 'yay') // logging!
  cacOpts.where // => undefined (testable warning?)
  cacOpts.where = './eh' // './eh' (assign anything? warn?)
  opts.where // => './' (unaltered by child)
  opts.cache // => undefined (test warn?)
}

PacoteOpts.allOpts() // => { log: { type: ... }, where: ..., retry: ..., cache: ..., auth: ... }