package notificator

import (
	"context"
	"sync"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/morph/event"
	"git.frostfs.info/TrueCloudLab/frostfs-s3-lifecycler/internal/logs"
	"go.uber.org/zap"
)

// handlerLimiter is a limiter to make some works to be sequential
// and interrupt previous one if new one is submitted.
type handlerLimiter struct {
	ctx     context.Context
	log     *zap.Logger
	handler NewEpochHandler
	work    chan func()

	mu            sync.Mutex
	cancelCurrent context.CancelFunc
}

func newHandlerLimiter(ctx context.Context, handler NewEpochHandler, log *zap.Logger) *handlerLimiter {
	hl := &handlerLimiter{
		ctx:           ctx,
		log:           log,
		handler:       handler,
		work:          make(chan func()),
		cancelCurrent: func() {},
	}

	go hl.start(ctx)

	return hl
}

func (h *handlerLimiter) start(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			close(h.work)
			return
		case work := <-h.work:
			work()
		}
	}
}

func (h *handlerLimiter) replaceCurrentWorkContext(ctx context.Context) (workCtx context.Context) {
	h.mu.Lock()
	defer h.mu.Unlock()

	h.cancelCurrent()
	workCtx, h.cancelCurrent = context.WithCancel(ctx)

	return workCtx
}

func (h *handlerLimiter) Handler(e event.Event) {
	ee, ok := e.(NewEpochEvent)
	if !ok {
		return
	}

	workCtx := h.replaceCurrentWorkContext(h.ctx)
	h.log.Debug(logs.NewEpochWasTriggered, zap.Uint64("epoch", ee.Epoch))
	h.work <- func() {
		h.handler(workCtx, ee)
	}
}