package dbUtils

// A combination of worker pool and a queue

import (
	"context"
	"sync"
	"time"

	common "git.mic.pp.ua/anderson/nettools/common"
)

type WorkersCount struct {
	Lim  int32
	Busy int32
}

type IWorkerPool interface {
	Exec(task common.Task)
	QueueLen() int
	WorkersCount() WorkersCount
	SetWorkersCountLim(newSize int32)
}

// Just a worker pool with queue before it
// Thread-safe
type WorkerPool struct {
	TaskQueue    []common.Task
	Mu           *sync.RWMutex
	CountLim     int32
	CountBusy    int32
	TaskDeadline time.Duration
}

func NewWorkerPool(workersCountLim int32, taskDeadline time.Duration) *WorkerPool {
	return &WorkerPool{
		TaskQueue:    []common.Task{},
		Mu:           &sync.RWMutex{},
		CountLim:     workersCountLim,
		CountBusy:    0,
		TaskDeadline: taskDeadline,
	}
}

func (wpq *WorkerPool) Exec(task common.Task) {
	wpq.Mu.Lock()
	if wpq.CountBusy >= wpq.CountLim {
		wpq.TaskQueue = append(wpq.TaskQueue, task)
		return
	}
	wpq.CountBusy++
	wpq.Mu.Unlock()
	for {
		var cancel context.CancelFunc
		var ctx context.Context
		if wpq.TaskDeadline != 0 {
			ctx = context.Background()
			ctx, cancel = context.WithTimeout(ctx, wpq.TaskDeadline)
			defer cancel()
		}
		task(ctx)
		wpq.Mu.Lock()
		if len(wpq.TaskQueue) < 1 {
			wpq.CountBusy--
			wpq.Mu.Unlock()
			return
		}
		task = wpq.TaskQueue[0]
		wpq.TaskQueue = wpq.TaskQueue[1:]
		wpq.Mu.Unlock()
	}
}

func (wpq *WorkerPool) QueueLen() int {
	wpq.Mu.RLock()
	defer wpq.Mu.RUnlock()
	return len(wpq.TaskQueue)
}

func (wpq *WorkerPool) WorkersCount() WorkersCount {
	wpq.Mu.RLock()
	defer wpq.Mu.RUnlock()
	return WorkersCount{
		Lim:  wpq.CountLim,
		Busy: wpq.CountBusy,
	}
}

func (wpq *WorkerPool) SetWorkersCountLim(newSize int32) {
	wpq.Mu.Lock()
	wpq.CountLim = newSize
	wpq.Mu.Unlock()
}