Created
September 14, 2023 05:45
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declare const historyIdBrand: unique symbol; | |
let historyId = 0; | |
type HistoryId = number & { [historyIdBrand]: never }; | |
interface HistoryItem<T, A> { | |
readonly id: HistoryId; | |
readonly action: A; | |
readonly state: T; | |
} | |
type Mutate<T, A> = (state: T, action: A) => T; | |
class RevokableHistory<T, A> { | |
readonly #initialState: T; | |
readonly #history: HistoryItem<T, A>[] = [] | |
readonly #mutate: Mutate<T, A>; | |
constructor(initialState: T, mutate: Mutate<T, A>) { | |
this.#initialState = initialState; | |
this.#mutate = mutate; | |
} | |
getLastState(): T { | |
return this.#history.at(-1)?.state ?? this.#initialState; | |
} | |
push(action: A): HistoryItem<T, A> { | |
const item: HistoryItem<T, A> = { | |
id: historyId++ as HistoryId, | |
action, | |
state: this.#mutate(this.getLastState(), action), | |
} | |
this.#history.push(item); | |
return item; | |
} | |
revoke(id: HistoryId): void { | |
const revokedHistoryIndex = this.#history.findIndex((item) => item.id == id); | |
if (revokedHistoryIndex == -1) { | |
throw new TypeError(); | |
} | |
const [_revoked, ...histories] = this.#history.splice(revokedHistoryIndex, Infinity); | |
for (const history of histories) { | |
this.push(history.action); | |
} | |
} | |
} | |
(() => { | |
const h = new RevokableHistory("", (leading, trailing: string) => leading + trailing); | |
console.log(h.getLastState()); //=> "" | |
h.push("1"); | |
const { id } = h.push("2"); | |
h.push("3"); | |
console.log(h.getLastState()); //=> "123" | |
h.revoke(id); | |
console.log(h.getLastState()); //=> "13" | |
})(); |
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