package worker

import (
	"context"
	"sync"
	"time"

	"code.nochebuena.dev/go/launcher"
	"code.nochebuena.dev/go/logz"
)

// Task is a unit of work executed asynchronously by the worker pool.
type Task func(ctx context.Context) error

// Provider dispatches tasks to the pool.
type Provider interface {
	// Dispatch queues a task. Returns false if the queue is full (backpressure).
	Dispatch(task Task) bool
}

// Component adds lifecycle management to Provider.
type Component interface {
	launcher.Component
	Provider
}

// Config holds worker pool settings.
type Config struct {
	// PoolSize is the number of concurrent workers. Default: 5.
	PoolSize int `env:"WORKER_POOL_SIZE" envDefault:"5"`
	// BufferSize is the task queue capacity. Default: 100.
	BufferSize int `env:"WORKER_BUFFER_SIZE" envDefault:"100"`
	// TaskTimeout is the maximum duration for a single task. Zero = no timeout.
	TaskTimeout time.Duration `env:"WORKER_TASK_TIMEOUT" envDefault:"0s"`
	// ShutdownTimeout is how long OnStop waits for workers to drain. Default: 30s.
	ShutdownTimeout time.Duration `env:"WORKER_SHUTDOWN_TIMEOUT" envDefault:"30s"`
}

type workerComponent struct {
	logger    logz.Logger
	cfg       Config
	taskQueue chan Task
	wg        sync.WaitGroup
	ctx       context.Context
	cancel    context.CancelFunc
}

// New returns a worker Component. Call lc.Append(pool) to manage its lifecycle.
func New(logger logz.Logger, cfg Config) Component {
	if cfg.PoolSize <= 0 {
		cfg.PoolSize = 5
	}
	if cfg.BufferSize <= 0 {
		cfg.BufferSize = 100
	}
	ctx, cancel := context.WithCancel(context.Background())
	return &workerComponent{
		logger:    logger,
		cfg:       cfg,
		taskQueue: make(chan Task, cfg.BufferSize),
		ctx:       ctx,
		cancel:    cancel,
	}
}

func (w *workerComponent) OnInit() error {
	w.logger.Info("worker: initializing pool",
		"pool_size", w.cfg.PoolSize,
		"buffer_size", w.cfg.BufferSize)
	return nil
}

func (w *workerComponent) OnStart() error {
	w.logger.Info("worker: starting workers")
	for i := 0; i < w.cfg.PoolSize; i++ {
		w.wg.Add(1)
		go func(id int) {
			defer w.wg.Done()
			w.runWorker(id)
		}(i)
	}
	return nil
}

func (w *workerComponent) OnStop() error {
	w.logger.Info("worker: stopping, draining queue")
	close(w.taskQueue)
	w.cancel()

	done := make(chan struct{})
	go func() { w.wg.Wait(); close(done) }()

	timeout := w.cfg.ShutdownTimeout
	if timeout == 0 {
		timeout = 30 * time.Second
	}
	select {
	case <-done:
		w.logger.Info("worker: all workers stopped cleanly")
	case <-time.After(timeout):
		w.logger.Error("worker: shutdown timeout reached; some workers may still be running", nil)
	}
	return nil
}

func (w *workerComponent) Dispatch(task Task) bool {
	select {
	case w.taskQueue <- task:
		return true
	default:
		w.logger.Error("worker: queue full, task dropped", nil)
		return false
	}
}

func (w *workerComponent) runWorker(id int) {
	for task := range w.taskQueue {
		ctx := w.ctx
		var cancel context.CancelFunc
		if w.cfg.TaskTimeout > 0 {
			ctx, cancel = context.WithTimeout(ctx, w.cfg.TaskTimeout)
		} else {
			cancel = func() {}
		}
		if err := task(ctx); err != nil {
			w.logger.Error("worker: task failed", err, "worker_id", id)
		}
		cancel()
	}
}