mobx-keystone-mindreframer/src/wrappers/asSet.ts

A MobX powered state management solution based on data trees with first class support for Typescript, snapshots, patches and much more

import {
  action,
  intercept,
  IObservableArray,
  ISetWillChange,
  isObservableArray,
  observable,
  ObservableSet,
  observe,
} from "mobx"
import { assertIsObservableArray, assertIsSet, failure, inDevMode } from "../utils"
import { Lock } from "../utils/lock"
import { tag } from "../utils/tag"

const observableSetBackedByObservableArray = action(
  <T>(array: IObservableArray<T>): ObservableSet<T> & { dataObject: typeof array } => {
    if (inDevMode()) {
      if (!isObservableArray(array)) {
        throw failure("assertion failed: expected an observable array")
      }
    }

    const set = observable.set(array)
    ;(set as any).dataObject = array

    if (set.size !== array.length) {
      throw failure("arrays backing a set cannot contain duplicate values")
    }

    const mutationLock = new Lock()

    // for speed reasons we will just assume distinct values are only once in the array

    // when the array changes the set changes
    observe(
      array,
      action(
        mutationLock.unlockedFn((change: any /*IArrayDidChange<T>*/) => {
          switch (change.type) {
            case "splice": {
              {
                const removed = change.removed
                for (let i = 0; i < removed.length; i++) {
                  set.delete(removed[i])
                }
              }

              {
                const added = change.added
                for (let i = 0; i < added.length; i++) {
                  set.add(added[i])
                }
              }

              break
            }

            case "update": {
              set.delete(change.oldValue)
              set.add(change.newValue)
              break
            }
          }
        })
      )
    )

    // when the set changes also change the array
    intercept(
      set,
      action((change: ISetWillChange<T>) => {
        if (!mutationLock.isLocked) {
          return null // already changed
        }

        switch (change.type) {
          case "add": {
            array.push(change.newValue)
            break
          }

          case "delete": {
            const i = array.indexOf(change.oldValue)
            if (i >= 0) {
              array.splice(i, 1)
            }
            break
          }
        }

        return change
      })
    )

    return set as any
  }
)

const asSetTag = tag((array: Array<any>) => {
  assertIsObservableArray(array, "array")
  return observableSetBackedByObservableArray(array)
})

/**
 * Wraps an observable array to offer a set like interface.
 *
 * @param array
 */
export function asSet<T>(array: Array<T>): ObservableSet<T> & { dataObject: typeof array } {
  return asSetTag.for(array) as any
}

/**
 * Converts a set to an array. If the set is a collection wrapper it will return the backed array.
 *
 * @param set
 */
export function setToArray<T>(set: Set<T>): Array<T> {
  assertIsSet(set, "set")

  const dataObject = (set as any).dataObject
  if (dataObject) {
    return dataObject
  }

  return Array.from(set.values())
}