55 lines
1.6 KiB
TypeScript
55 lines
1.6 KiB
TypeScript
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import type Ticker from '../Ticker'
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import Emitter from '../utils/Emitter'
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import type {default as Tappable} from '../utils/Tappable'
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import type {IDerivation} from './IDerivation'
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export default class DerivationEmitter<V> {
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private _derivation: IDerivation<V>
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private _ticker: Ticker
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private _emitter: Emitter<V>
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private _lastValue: undefined | V
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private _lastValueRecorded: boolean
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private _hadTappers: boolean
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constructor(derivation: IDerivation<V>, ticker: Ticker) {
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this._derivation = derivation
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this._ticker = ticker
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this._emitter = new Emitter()
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this._emitter.onNumberOfTappersChange(() => {
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this._reactToNumberOfTappersChange()
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})
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this._hadTappers = false
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this._lastValueRecorded = false
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this._lastValue = undefined
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return this
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}
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private _possiblyMarkAsStale = () => {
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this._ticker.onThisOrNextTick(this._refresh)
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}
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private _reactToNumberOfTappersChange() {
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const hasTappers = this._emitter.hasTappers()
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if (hasTappers !== this._hadTappers) {
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this._hadTappers = hasTappers
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if (hasTappers) {
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this._derivation.addDependent(this._possiblyMarkAsStale)
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} else {
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this._derivation.removeDependent(this._possiblyMarkAsStale)
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}
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}
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}
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tappable(): Tappable<V> {
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return this._emitter.tappable
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}
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private _refresh = () => {
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const newValue = this._derivation.getValue()
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if (newValue === this._lastValue && this._lastValueRecorded === true) return
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this._lastValue = newValue
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this._lastValueRecorded = true
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this._emitter.emit(newValue)
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}
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}
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