const METADATA_KEY = Symbol('unspoken:index')

export type PropertyCallback = {(target:object, propertyKey:string):void}
export type NewableAny       = {new(...params:any[]):any}
export type Newable<T>       = {new(...params:any[]):T}
export type NewableNoArgs<T> = {new():T}

export type IndexAtMeta = {
  propertyKey:string,
  typeHint?:NewableAny,
  isArray:boolean
}

export function getIndexStore(target:object) {
  let store:(IndexAtMeta[] | undefined) = Reflect.getOwnMetadata(METADATA_KEY, target)

  if (!store) {
    store = new Array<IndexAtMeta>()

    // If this is the first time we're defining a metadata store for this
    // object, get the superclass's metadata first, and merge it into our
    // store.
    const superStore = Reflect.getMetadata(METADATA_KEY, target)
    if (superStore !== undefined && Array.isArray(superStore)) {
      store.push(...superStore)
    }

    Reflect.defineMetadata(METADATA_KEY, store, target)
  }

  return store
}

export function getIndexingMetas(origin:Object):IndexAtMeta[] {
  // This function returns metadata about which fields are
  // indexed on an object, and in which order.

  // Note: If a class extends an Unspoken object but doesn't
  // define any of its own fields, then we need to get indexing
  // data from the superclass.

  // The following first checks the object for metadata,
  // then the superclass, then finally fails gracefully

  return Reflect.getOwnMetadata(METADATA_KEY, origin) ??
         Reflect.getMetadata(METADATA_KEY, origin) ??
         []
}