concurrency with promises

concurrency with promises

const delay = second => () => new Promise((resolve, rejects) => {
        setTimeout(() => {
            resolve()
        }, second * 1000); 
   })

// some tasks that take long time
let tasks = [
	delay(0),
	delay(3),
	delay(3),
	delay(3),
	delay(1),
	delay(1),
	delay(1),
	delay(3),
	delay(3),
	delay(3),
	delay(3),
	delay(3)
]


class PromiseQueue{
	constructor(tasks = [], concurrent = 1){
		this.tasks = tasks 
		this.running = []
		this.complete = []
		this.concurrent = concurrent
	}

	isRunning(){
		return (this.running.length < this.concurrent ) && (this.tasks.length !== 0 )
	}

	run(){
		return new Promise((resolve,reject)=>{
			let start = () => {
				this.graph()//logging proccess
        
				while(this.isRunning()){
					const job = this.tasks.shift()
					  job().then(() => {
					  	//job is done? remove it from running queue, add to complete queue then start next job that remains
				  		this.complete.push(this.running.shift())
				  		start()
					  })

					this.running.push(job)
					this.graph()

				}
				if(this.running.length == 0){
					 resolve("done")
				}
			}

			start()

		})//promise

	}

	graph(){
		console.clear()
		console.log(`
			tasks: ${this.tasks.map(x => "❌")}
			running: ${this.running.map(x => "🔄")}
			completed: ${this.complete.map(x => "✔")}
		`)
	}

}// class


const queue = new PromiseQueue(tasks, 3)// how many jobs need to run together
	queue.run().then((arr) => {
		console.log(arr)
		console.log("\x07");// beeep sound
	})