package service

import (
	"context"
	"sync"
	"time"

	"apskel-pos-be/internal/logger"
)

// Lots expire at the end of their day, so running every quarter of an hour keeps any
// lot from staying past its expiry for more than about that long (PC-503).
const defaultWalletExpiryInterval = 15 * time.Minute

type walletExpiryWork interface {
	ExpireDue(ctx context.Context) (int, error)
	SendReminders(ctx context.Context) (int, error)
}

// WalletExpiryJob expires the balances whose time is up and reminds customers of what
// is about to (docs/prd-point-coin.md F12, PC-503, PC-504).
// Unlike OmsetMilestoneScheduler it keeps no state in memory: several instances can
// run it at once, and a restart repeats nothing, because every lot is expired under
// its wallet's lock with an idempotency key.
type WalletExpiryJob struct {
	expirer  walletExpiryWork
	stopCh   chan struct{}
	stopOnce sync.Once
}

func NewWalletExpiryJob(expirer walletExpiryWork) *WalletExpiryJob {
	return &WalletExpiryJob{expirer: expirer, stopCh: make(chan struct{})}
}

func (j *WalletExpiryJob) Start(interval time.Duration) {
	if interval <= 0 {
		interval = defaultWalletExpiryInterval
	}
	go func() {
		j.RunOnce(context.Background())
		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ticker.C:
				j.RunOnce(context.Background())
			case <-j.stopCh:
				return
			}
		}
	}()
	logger.NonContext.Infof("Wallet expiry job started (interval: %s)", interval)
}

func (j *WalletExpiryJob) Stop() {
	j.stopOnce.Do(func() { close(j.stopCh) })
}

// RunOnce expires what is due, sends the reminders that are due, and returns how many
// lots it expired.
func (j *WalletExpiryJob) RunOnce(ctx context.Context) int {
	expired, err := j.expirer.ExpireDue(ctx)
	if err != nil {
		logger.NonContext.Error("Wallet expiry failed to run", err)
	}
	if expired > 0 {
		logger.NonContext.Infof("Wallet expiry expired %d lots", expired)
	}
	reminded, err := j.expirer.SendReminders(ctx)
	if err != nil {
		logger.NonContext.Error("Wallet expiry reminders failed to run", err)
	}
	if reminded > 0 {
		logger.NonContext.Infof("Wallet expiry sent %d reminders", reminded)
	}
	return expired
}