From f1cb8edc91ea56a0f9162cb436402521f711de10 Mon Sep 17 00:00:00 2001
From: Aria Minaei <aria.minaei@gmail.com>
Date: Thu, 1 Dec 2022 13:33:52 +0100
Subject: [PATCH] Simplify `Derivation.onStale()`

---
 .../derivations/DerivationValuelessEmitter.ts | 51 -------------------
 .../dataverse/src/derivations/prism/prism.ts  |  8 ++-
 2 files changed, 6 insertions(+), 53 deletions(-)
 delete mode 100644 packages/dataverse/src/derivations/DerivationValuelessEmitter.ts

diff --git a/packages/dataverse/src/derivations/DerivationValuelessEmitter.ts b/packages/dataverse/src/derivations/DerivationValuelessEmitter.ts
deleted file mode 100644
index 45d8c9b..0000000
--- a/packages/dataverse/src/derivations/DerivationValuelessEmitter.ts
+++ /dev/null
@@ -1,51 +0,0 @@
-import Emitter from '../utils/Emitter'
-import type {default as Tappable} from '../utils/Tappable'
-import type {IDerivation} from './IDerivation'
-
-/**
- * Like DerivationEmitter, but with a different performance model. DerivationValuelessEmitter emits every time the
- * derivation is updated, even if the value didn't change, and tappers are called without the value. The advantage of
- * this is that you have control over when the underlying derivation is freshened, it won't automatically be freshened
- * by the emitter.
- */
-export default class DerivationValuelessEmitter<V> {
-  _derivation: IDerivation<V>
-  _emitter: Emitter<void>
-  _hadTappers: boolean
-
-  constructor(
-    derivation: IDerivation<V>,
-    readonly dontEmitValues: boolean = false,
-  ) {
-    this._derivation = derivation
-    this._emitter = new Emitter()
-    this._emitter.onNumberOfTappersChange(() => {
-      this._reactToNumberOfTappersChange()
-    })
-    this._hadTappers = false
-    return this
-  }
-
-  private _possiblyMarkAsStale = () => {
-    this._emitter.emit(undefined)
-  }
-
-  _reactToNumberOfTappersChange() {
-    const hasTappers = this._emitter.hasTappers()
-    if (hasTappers !== this._hadTappers) {
-      this._hadTappers = hasTappers
-      if (hasTappers) {
-        this._derivation.addDependent(this._possiblyMarkAsStale)
-      } else {
-        this._derivation.removeDependent(this._possiblyMarkAsStale)
-      }
-    }
-  }
-
-  /**
-   * The tappable associated with the emitter. You can use it to tap (subscribe to) the underlying derivation.
-   */
-  tappable(): Tappable<void> {
-    return this._emitter.tappable
-  }
-}
diff --git a/packages/dataverse/src/derivations/prism/prism.ts b/packages/dataverse/src/derivations/prism/prism.ts
index d3cd2fe..dfaf6d7 100644
--- a/packages/dataverse/src/derivations/prism/prism.ts
+++ b/packages/dataverse/src/derivations/prism/prism.ts
@@ -3,7 +3,6 @@ import type {$IntentionalAny, VoidFn} from '../../types'
 import Stack from '../../utils/Stack'
 import type Tappable from '../../utils/Tappable'
 import DerivationEmitter from '../DerivationEmitter'
-import DerivationValuelessEmitter from '../DerivationValuelessEmitter'
 import type {IDerivation} from '../IDerivation'
 import {isDerivation} from '../IDerivation'
 import {
@@ -235,7 +234,12 @@ class PrismDerivation<V> implements IDerivation<V> {
    * Returns a tappable that fires every time the prism's state goes from `fresh-\>stale.`
    */
   onStale(callback: () => void): VoidFn {
-    return new DerivationValuelessEmitter(this).tappable().tap(callback)
+    const untap = () => {
+      this.removeDependent(fn)
+    }
+    const fn = () => callback()
+    this.addDependent(fn)
+    return untap
   }
 
   /**