package threadpool

import (
	"log/slog"
	"runtime"
	"time"

	"github.com/alitto/pond/v2"
)

type ConfigProvider interface {
	GetMaxWorkers() int
	GetThreadMonitorInterval() int
	GetThreadPool() pond.Pool
	ThreadPoolStopAndWait()
	StartThreadPool(*slog.Logger)
}

type ThreadPoolConfig struct {
	MaxWorkers      int `env:"MAX_WORKERS"`
	MonitorInterval int `env:"THREAD_MONITOR_INTERVAL"`
	pool            pond.Pool
	stopMonitor     chan struct{}
	logger          *slog.Logger
}

type PoolMetrics struct {
	QueueUtilization float64
	AverageWaitTime  time.Duration
	ProcessingTime   time.Duration
}

func (dp *ThreadPoolConfig) StartThreadPool(logger *slog.Logger) {
	dp.logger = logger

	if dp.MaxWorkers <= 0 {
		dp.MaxWorkers = runtime.NumCPU() * 10
	}

	if dp.MonitorInterval <= 0 {
		dp.MonitorInterval = 120
	}

	dp.stopMonitor = make(chan struct{})
	dp.pool = pond.NewPool(dp.MaxWorkers)

	// Start the monitoring heartbeat
	dp.pool.Submit(dp.monitor)
}

// Log thread pool stats
func (dp *ThreadPoolConfig) monitor() {
	ticker := time.NewTicker(time.Duration(dp.MonitorInterval) * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-dp.stopMonitor:
			return
		case <-ticker.C:
			dp.logger.Debug(
				"thread pool heartbeat",
				"running_workers",
				dp.pool.RunningWorkers(),
				"queue_size",
				dp.pool.QueueSize(),
				"submitted_tasks",
				dp.pool.SubmittedTasks(),
				"waiting_tasks",
				dp.pool.WaitingTasks(),
				"dropped_tasks",
				dp.pool.DroppedTasks(),
			)
		}
	}
}

func (dp *ThreadPoolConfig) GetMaxWorkers() int {
	return dp.MaxWorkers
}

func (dp *ThreadPoolConfig) GetThreadMonitorInterval() int {
	return dp.MonitorInterval
}

func (dp *ThreadPoolConfig) GetThreadPool() pond.Pool {
	if dp.pool == nil {
		dp.StartThreadPool(slog.Default())
	}

	return dp.pool
}

func (dp *ThreadPoolConfig) ThreadPoolStopAndWait() {
	waitCh := make(chan struct{})
	go func() {
		close(dp.stopMonitor)

		dp.pool.StopAndWait()

		close(waitCh)
	}()

	timeout := 3 * time.Second
	select {
	case <-waitCh:
		dp.logger.Info("thread pool shutdown complete")
	case <-time.After(timeout):
		dp.logger.Error("thread pool shotdown timeout")
	}
}