partial.ts

import { optional } from './optional'
import { internalRecord } from './record'
import { InternalRuntype, Runtype, RuntypeUsageError } from './runtype'

/**
 * Build a new record runtype that marks all keys as optional.
 *
 * This is the runtype counterpart to `Partial<T>`.
 */
export function partial<T>(original: Runtype<T>): Runtype<Partial<T>> {
  const fields = (original as InternalRuntype<any>).meta?.fields
  const isNonStrict = (original as InternalRuntype<any>).meta?.isNonStrict

  if (!fields) {
    throw new RuntypeUsageError(`expected a record runtype`)
  }

  const newRecordFields: any = {}

  for (const k in fields) {
    if (Object.prototype.hasOwnProperty.call(fields, k)) {
      // TODO: detect whether field is already optional and do not apply
      // optional a second time
      newRecordFields[k] = optional(fields[k])
    }
  }

  return internalRecord(newRecordFields, isNonStrict)
}