example-race.nut

// MIT License
//
// Copyright 2020-23 KOIRE Wireless
// Copyright 2016-19 Electric Imp
//
// SPDX-License-Identifier: MIT
//
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/**
 * The example demonstrates a parking assistance application.
 *
 * There are three different parkings lots near a shopping center.
 * Each parking lot has its own software API with different methods to find a place.
 * We call three different methods in parallel using race().
 * As soon as any method finds a spot, `then()` handler is triggered.
 */

#require "Promise.lib.nut:4.0.1"

// max value for random generator
const MAX = 20;

// For each method we make random delay
function checkSlot(prefix, found) {
    // When a place is found, call `found(placeId)`
    // with the found slot id as the first argument
    local delay = math.rand() % MAX + 2;
    local place = prefix + (math.rand() % MAX);
    imp.wakeup(delay, function() {
        found(place)
    });
}

function checkParkingA() {
    return Promise(function (resolve, reject) {
        checkSlot("A", resolve);
    });
}

function checkParkingB() {
    return Promise(function (resolve, reject) {
        checkSlot("B", resolve);
    });
}

function checkParkingC() {
    return Promise(function (resolve, reject) {
        checkSlot("C", resolve);
    });
}

server.log("Looking for a place available...");
Promise.race([checkParkingA, checkParkingB, checkParkingC])
.then(function(place) {
    server.log("Found place: " + place);
})