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Add defer operator #330

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Add defer operator #330

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30 changes: 30 additions & 0 deletions src/defer/index.ts
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import { Store, Unit, merge, sample } from 'effector';
import { combineEvents } from '../combine-events';
import { not } from '../not';

export interface DeferArgs {
clock: Unit<any>;
until: Store<boolean>;
}

export const defer = (args: DeferArgs) => {
const { clock, until: condition } = args;

const calledAfterCondition = sample({
clock: clock,
filter: condition,
});

const calledBeforeCondition = sample({
clock: clock,
filter: not(condition),
});

return merge([
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@velialiev velialiev May 16, 2024 •
edited
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there could be 4 cases:

  1. Event called, condition is true --> call event
  2. Event called, condition is false --> wait until condition will be true and call event
  3. Condition became true, event is not called yet --> wait until event is called
  4. Condition became false, event is not called yet --> reset the state and wait both for event and condition to become true

IMPORTANT: if clock will be called more than 1 time only the last event will be deferred and called. Other events will be ignored

calledAfterCondition,
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if condition is already true then call event immediately

combineEvents({
events: [calledBeforeCondition, condition.updates.filter({ fn: Boolean })],
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if condition is not true yet then defer event call until condition became true

reset: condition.updates.filter({ fn: (value) => !value }),
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if condition became true and then false we should reset combine events since event call should be deferred until condition will be true again

}),
]);
};
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