create a simple, message-based abstract validator

createValidator.ts

type ValidateRuleFn<T> = (data: T) => string[] | null

type Priority = 'WARN' | 'ERROR'

type RuleTuple<T> = [priority: Priority, validateRule: ValidateRuleFn<T>]

type ValidationResult = { errors: string[], warnings: string[] }

const RESULT_KEYS: Record<Priority, string> = {
  ERROR: 'errors',
  WARN: 'warnings'
}

const VALID_PRIORITIES: Priority[] = ['ERROR', 'WARN']

const createValidator = <T>(...entries: Array<RuleTuple<T>>) => {
  if (!structuredClone) {
    throw new ReferenceError('structuredClone should be supported!')
  }

  if (!entries.every(([priority]) => VALID_PRIORITIES.includes(priority))) {
    throw new TypeError('there are invalid priorities')
  }

  return (data: T) => entries.reduce<ValidationResult>(
    (acc, [priority, validateRule]) => {
      const result = validateRule(structuredClone(data))

      if (!result) return acc

      const resultKey = Reflect.get(RESULT_KEYS, priority)

      return {
        ...acc,
        [resultKey]: [...acc[resultKey], result]
      }
    },
    { errors: [], warnings: [] }
  )
}