atomico/src/use-state-generator/use-state-generator.js

Atomico is a small library for the creation of interfaces based on web-components, only using functions and hooks.

import { useState, useMemo, useEffect } from "../core/core";
import { isFunction, promise } from "../core/utils";
import { ARRAY_EMPTY } from "../core/constants";

const promiseIgnore = promise(() => {});

export const CONTINUE = Symbol();

export function delay(ms) {
    return promise(resolve => setTimeout(() => resolve(CONTINUE), ms));
}

export function useStateGenerator(stream, initialState, vars = ARRAY_EMPTY) {
    let [{ ref }, setValue] = useState(() => ({
        ref: createState(initialState)
    }));

    useEffect(() => ref.cancel, []);

    ref.stream = stream;

    return [
        ref.state,
        useMemo(
            () =>
                ref.send(() => {
                    setValue({ ref });
                }),
            vars
        )
    ];
}

function consumer(value, process, id, subscribe) {
    return Promise.resolve(value).then(value => {
        if (isFunction(value)) {
            return consumer(value(process.state), process, id, subscribe);
        }

        if (typeof value == "object" && isFunction(value.next)) {
            return promise(resolve => {
                function scan(generator) {
                    Promise.resolve(
                        generator.next(process.state)
                    ).then(({ value, done }) =>
                        consumer(value, process, id, subscribe).then(() =>
                            done ? resolve(process.state) : scan(generator)
                        )
                    );
                }
                scan(value);
            });
        }
        return process.next(value, subscribe, id);
    });
}

function createState(state) {
    let currentID = 0;
    let process = { state, next, cancel, send };

    function next(value, subscribe, id) {
        if (id != currentID) return promiseIgnore;
        if (value != CONTINUE) {
            process.state = value;
            subscribe && subscribe(value);
        }
        return process.state;
    }
    function cancel() {
        currentID++;
    }
    function send(subscribe) {
        return consumer(process.stream, process, ++currentID, subscribe);
    }

    return process;
}