semaphore.js

const StateMachine = require("fsm-async");
const chalk = require("chalk");

class Semaphore extends StateMachine {
    constructor() {
        const transitionTable = {
            initial: "init",
            transitions: [
                { ev: "init", from: "init", to: "red" },
                { ev: "_red", from: "red", to: "fromRed" },
                { ev: "toGreen", from: "fromRed", to: "green" },
                { ev: "_green", from: "green", to: "fromGreen" },
                { ev: "toRed", from: "fromGreen", to: "red" }
            ]
        };
        super(transitionTable);
        this.counter = 0;
    }

    async _onRed() {
        if (this.counter) process.exit();
    }

    async onGreen() {
        console.log(`${chalk.bgGreen.bold("onGreen")}`);
        // Instead of really disconnecting we simulate it here
        await new Promise(resolve => setTimeout(resolve, 2000));
        this._green();
    }

    async onFromRed() {
        console.log(`${chalk.bgYellow.bold("onFromRed")}`, this.getState());
        await new Promise(resolve => setTimeout(resolve, 1000));
        this.toGreen();
    }

    async onFromGreen() {
        console.log(`${chalk.bgYellow.bold("onFromGreen")}`, this.getState());
        await new Promise(resolve => setTimeout(resolve, 1000));
        this.toRed();
    }

    async onRed() {
        console.log(`${chalk.bgRed.bold("onRed")}`);
        // Instead of really connecting we simulate it here
        await new Promise(resolve => setTimeout(resolve, 5000));
        this._red();
        this.counter++;
    }
}

module.exports = Semaphore;