package pool

import (
	"github.com/cespare/xxhash/v2"
)

type WorkerPool struct {
	maxWorkers  int
	taskQueue   []chan func()
	stoppedChan chan struct{}
}

func New(maxWorkers int) *WorkerPool {
	// There must be at least one worker.
	if maxWorkers < 1 {
		maxWorkers = 1
	}

	// taskQueue is unbuffered since items are always removed immediately.
	pool := &WorkerPool{
		taskQueue:   make([]chan func(), maxWorkers),
		maxWorkers:  maxWorkers,
		stoppedChan: make(chan struct{}),
	}
	// Start the task dispatcher.
	pool.dispatch()

	return pool
}

func (p *WorkerPool) Submit(uid string, task func()) {
	idx := xxhash.Sum64([]byte(uid)) % uint64(p.maxWorkers)
	if task != nil {
		p.taskQueue[idx] <- task
	}
}

func (p *WorkerPool) dispatch() {
	for i := 0; i < p.maxWorkers; i++ {
		p.taskQueue[i] = make(chan func(), 1024)
		go startWorker(p.taskQueue[i])
	}
}

func startWorker(taskChan chan func()) {
	var task func()
	var ok bool
	for {
		task, ok = <-taskChan
		if !ok {
			break
		}
		// Execute the task.
		task()
	}
}