package rep

import (
	"log"
	"time"
)

func (rep *Replicator) runWALFollower() {
	defer rep.done.Done()

	for {
		rep.followOnce()

		select {
		case <-rep.stop:
			return
		default:
			time.Sleep(time.Second)
		}
	}
}

func (rep *Replicator) followOnce() {
	logf := func(pattern string, args ...any) {
		log.Printf("[WAL-FOLLOWER] "+pattern, args...)
	}

	state := rep.getState()
	it, err := rep.wal.Iterator(state.SeqNum + 1)
	if err != nil {
		logf("Failed to create WAL iterator: %v", err)
		return
	}
	defer it.Close()

	for {
		select {
		case <-rep.stop:
			logf("Stopped")
			return
		default:
		}

		if it.Next(time.Second) {
			rec := it.Record()

			if err := rep.app.Apply(rec); err != nil {
				logf("App failed to apply change: %v", err)
				return
			}

			if err := rep.ack(rec.SeqNum, rec.TimestampMS); err != nil {
				logf("App failed to update local state: %v", err)
				return
			}

			select {
			case rep.appendNotify <- struct{}{}:
			default:
			}
		} else if it.Error() != nil {
			logf("Iteration error: %v", err)
			return
		}
	}
}