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Co-authored-by: Matvei Andrienko <m.y.andrienko@outlook.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,57 @@ | ||
| export type Patch<T> = (value: T) => T; | ||
| export type Handler<T> = (nextValue: T, previousValue: T | undefined) => void; | ||
| export type Unsubscribe = () => void; | ||
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| function isPatch<T>(value: T | Patch<T>): value is Patch<T> { | ||
| return typeof value === 'function'; | ||
| } | ||
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| export class StateStore<T extends Record<string, unknown>> { | ||
| private handlerSet = new Set<Handler<T>>(); | ||
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| constructor(private value: T) {} | ||
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| public next = (newValueOrPatch: T | Patch<T>): void => { | ||
| // newValue (or patch output) should never be mutated previous value | ||
| const newValue = isPatch(newValueOrPatch) ? newValueOrPatch(this.value) : newValueOrPatch; | ||
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| // do not notify subscribers if the value hasn't changed | ||
| if (newValue === this.value) return; | ||
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| const oldValue = this.value; | ||
| this.value = newValue; | ||
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| this.handlerSet.forEach((handler) => handler(this.value, oldValue)); | ||
| }; | ||
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| public partialNext = (partial: Partial<T>): void => this.next((current) => ({ ...current, ...partial })); | ||
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| public getLatestValue = (): T => this.value; | ||
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| public subscribe = (handler: Handler<T>): Unsubscribe => { | ||
| handler(this.value, undefined); | ||
| this.handlerSet.add(handler); | ||
| return () => { | ||
| this.handlerSet.delete(handler); | ||
| }; | ||
| }; | ||
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| public subscribeWithSelector = <O extends readonly unknown[]>(selector: (nextValue: T) => O, handler: Handler<O>) => { | ||
| // begin with undefined to reduce amount of selector calls | ||
| let selectedValues: O | undefined; | ||
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| const wrappedHandler: Handler<T> = (nextValue) => { | ||
| const newlySelectedValues = selector(nextValue); | ||
| const hasUpdatedValues = selectedValues?.some((value, index) => value !== newlySelectedValues[index]) ?? true; | ||
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| if (!hasUpdatedValues) return; | ||
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| const oldSelectedValues = selectedValues; | ||
| selectedValues = newlySelectedValues; | ||
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| handler(newlySelectedValues, oldSelectedValues); | ||
| }; | ||
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| return this.subscribe(wrappedHandler); | ||
| }; | ||
| } |
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