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import {useCallback, useEffect, useRef, useState} from 'react'
type Task<TServerState> = {
isOn: boolean
resolve: (serverState: TServerState) => void
reject: (e: unknown) => void
}
type TaskQueue<TServerState> = {
activeTask: Task<TServerState> | null
queuedTask: Task<TServerState> | null
}
function AbortError() {
const e = new Error()
e.name = 'AbortError'
return e
}
export function useToggleMutationQueue<TServerState>({
initialState,
runMutation,
onSuccess,
}: {
initialState: TServerState
runMutation: (
prevState: TServerState,
nextIsOn: boolean,
) => Promise<TServerState>
onSuccess: (finalState: TServerState) => void
}) {
// We use the queue as a mutable object.
// This is safe becuase it is not used for rendering.
const [queue] = useState<TaskQueue<TServerState>>({
activeTask: null,
queuedTask: null,
})
async function processQueue() {
if (queue.activeTask) {
// There is another active processQueue call iterating over tasks.
// It will handle any newly added tasks, so we should exit early.
return
}
// To avoid relying on the rendered state, capture it once at the start.
// From that point on, and until the queue is drained, we'll use the real server state.
let confirmedState: TServerState = initialState
try {
while (queue.queuedTask) {
const prevTask = queue.activeTask
const nextTask = queue.queuedTask
queue.activeTask = nextTask
queue.queuedTask = null
if (prevTask?.isOn === nextTask.isOn) {
// Skip multiple requests to update to the same value in a row.
prevTask.reject(new (AbortError as any)())
continue
}
try {
// The state received from the server feeds into the next task.
// This lets us queue deletions of not-yet-created resources.
confirmedState = await runMutation(confirmedState, nextTask.isOn)
nextTask.resolve(confirmedState)
} catch (e) {
nextTask.reject(e)
}
}
} finally {
onSuccess(confirmedState)
queue.activeTask = null
queue.queuedTask = null
}
}
function queueToggle(isOn: boolean): Promise<TServerState> {
return new Promise((resolve, reject) => {
// This is a toggle, so the next queued value can safely replace the queued one.
if (queue.queuedTask) {
queue.queuedTask.reject(new (AbortError as any)())
}
queue.queuedTask = {isOn, resolve, reject}
processQueue()
})
}
const queueToggleRef = useRef(queueToggle)
useEffect(() => {
queueToggleRef.current = queueToggle
})
const queueToggleStable = useCallback(
(isOn: boolean): Promise<TServerState> => {
const queueToggleLatest = queueToggleRef.current
return queueToggleLatest(isOn)
},
[],
)
return queueToggleStable
}
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