Created
September 15, 2023 09:32
-
-
Save ztrehagem/8b7866462e87592c404ec6ebcd828bae to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
interface Action<T, U = unknown> { | |
act: (state: T) => Promise<U>; | |
deriveActual: (state: T, actResult: U) => T; | |
deriveOptimistic: (state: T) => T; | |
} | |
export class OptimisticStore<T> { | |
#optimisticState: T; | |
#committedState: T; | |
readonly #runner = new SerialTaskRunner(); | |
readonly #actionQueue: Action<T>[] = []; | |
constructor(initialState: T) { | |
this.#optimisticState = initialState; | |
this.#committedState = initialState; | |
} | |
get latestState(): T { | |
return this.#optimisticState; | |
} | |
describe(): { stable: T; latest: T } { | |
return { stable: this.#committedState, latest: this.#optimisticState }; | |
} | |
async dispatch<U>(action: Action<T, U>): Promise<void> { | |
this.#actionQueue.push(action as Action<T>); | |
// derive optimistic state | |
this.#optimisticState = action.deriveOptimistic(this.#optimisticState); | |
try { | |
await this.#runner.offer(async () => { | |
try { | |
const result = await action.act(this.#committedState); | |
// derive next stable state with action result | |
this.#committedState = action.deriveActual( | |
this.#committedState, | |
result, | |
); | |
// re-derive optimistic state | |
this.#optimisticState = this.#actionQueue | |
.slice(1) | |
.reduce( | |
(state, action) => action.deriveOptimistic(state), | |
this.#committedState, | |
); | |
} catch (error) { | |
// rollback optimistic state to last committed state | |
this.#optimisticState = this.#committedState; | |
throw error; | |
} | |
}); | |
} finally { | |
// remove settled action from queue | |
this.#actionQueue.shift(); | |
} | |
} | |
} | |
class SerialTaskRunner { | |
#lastPromise: Promise<unknown> | null = null; | |
/** | |
* Reserve function call after preceded tasks unless one of them throws. | |
*/ | |
async offer<T>(fn: () => Promise<T>): Promise<T> { | |
const newPromise = this.#lastPromise?.then(fn) ?? fn(); | |
try { | |
return await (this.#lastPromise = newPromise); | |
} finally { | |
// Cleanup if there are no trailing promises. | |
if (this.#lastPromise == newPromise) { | |
this.#lastPromise = null; | |
} | |
} | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment