components.js

export { default as Vue } from 'vue'
export { mixins } from 'vue-class-component'

import $Component from 'vue-class-component'
import { Prop as $Prop, Watch as $Watch } from 'vue-property-decorator'

const isDescriptor = obj => obj?.[Symbol.toStringTag] === 'Descriptor'

export function Prop (...options) {
  const decorator = fieldDescriptor => {
    if (fieldDescriptor.initializer) {
      (options = options.length === 0 ? [{}] : options)[0].default = fieldDescriptor.initializer()
      fieldDescriptor.initializer = undefined
    }

    return {
      ...fieldDescriptor,
      finisher: klass => {
        $Prop(...options)(klass, fieldDescriptor.key, fieldDescriptor.descriptor)
        return klass
      }
    }
  }

  return isDescriptor(options[0])
    ? decorator(options.shift())
    : decorator
}

export function Watch (...options) {
  const decorator = fieldDescriptor => ({
    ...fieldDescriptor,
    finisher: klass => {
      $Watch(...options)(klass, fieldDescriptor.key, fieldDescriptor.descriptor)
      return klass
    }
  })

  return isDescriptor(options[0])
    ? decorator(options.shift())
    : decorator
}

export function Component (options) {
  const decorator = classDescriptor => ({
    ...classDescriptor,
    finisher: klass => {
      klass = $Component(options)(klass)

      const undefinedDataFields = {}

      for (const elementDescriptor of classDescriptor.elements) {
        const isUndefinedDataField = (
          elementDescriptor.kind === 'field' &&
          elementDescriptor.initializer?.() === undefined &&
          (klass.options.props === undefined || !(elementDescriptor.key in klass.options.props))
        )
        if (isUndefinedDataField) {
          undefinedDataFields[elementDescriptor.key] = undefined
        }
      }

      if (Object.getOwnPropertyNames(undefinedDataFields).length > 0) {
        const { options } = klass
        const { data } = options
        options.data = function (...args) {
          return data ? {
            ...this::data(...args),
            ...undefinedDataFields
          } : undefinedDataFields
        }
      }

      return klass
    }
  })

  return isDescriptor(options)
    ? decorator(options)
    : decorator
}