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highland-event-debouncer.js

'use strict';
const EventEmitter = require('events').EventEmitter;
const H = require('highland');

const emitter = new EventEmitter();

const delay = ({ key, value }) => {
    return H((push, next) => {
        H.log('----> REQUEST: ', key, value);
        setTimeout(() => {
            H.log('----> RESPONSE: ', key, value);
            push(null, { key, value });
            push(null, H.nil);
        }, Math.random() * 1000);
    });
};

const inFlight = new Set();

const updateStuff = ({ key, value }) => H.of({ key, value })
    .doto((x) => H.log('START', x.key, x.value, Date.now()))
    .flatMap(delay)
    .flatMap((x) => {
        if(x.value % 3 === 0) {
            H.log('---> 3 <---', x.key);
            return H([]);
        }
        return H.of(x);
    })
    .doto((x) => {
        if(x.value % 2 === 0) {
            throw new Error('BAM!');
        }
    })
    .doto((x) => H.log('DONE', x.key, x.value, Date.now()))
    .errors((err, push) => {
        H.log('ERROR', err.message, key, value, Date.now());
        push(null, { key, value });
    })
    .otherwise(() => {
        H.log('-> (Empty) <-');
        return H.of({ key, value });
    });



H('update', emitter)
    .map(updateStuff)
    .parallel(2)
    //.series()
    .doto((x) => {
        setTimeout(() => {
            inFlight.delete(x.key);
            H.log(`-> DELETED ${x.key}`);
        }, 5000);
    })
    .each(() => H.log('..............'));

emitter.on('blahonga', ({ key, value }) => {
    if (inFlight.has(key)) {
        //H.log(`${key} debounced.`);
        return;
    }

    inFlight.add(key);
    H.log(`-> ADDED ${key}`);
    setTimeout(() => {
        emitter.emit('update', { key, value });
    }, Math.random() * 1000);
});


setInterval(() => {
    emitter.emit('blahonga', {
        key: 'hello' + Math.floor(Math.random() * 3),
        value: Math.floor(Math.random() * 100000)
    });
}, 10);