import * as Y from 'yjs'
import {writable} from 'svelte/store'
import type {
  Readable,
  Writable,
} from 'svelte/store'

export const deriveUpdates = (
  doc: Y.Doc,
): Readable<Uint8Array> => {
  const updates: Writable<Uint8Array> = writable(
    Y.encodeStateAsUpdate(doc)
  )
  doc.on('update',
    (update: Uint8Array) => updates.set(update)
  )
  return {
    subscribe: updates.subscribe,
  }
}

export interface Unsubscriber {
  unsubscribe: () => void;
}

export const applyUpdates = (
  doc: Y.Doc,
  updates: Readable<Uint8Array>
): Unsubscriber => {
  const subscriber = (update: Uint8Array) => Y.applyUpdate(doc, update)
  return {
    unsubscribe: updates.subscribe(subscriber),
  }
}