package service

import (
	"context"
	"sync"
	"time"

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

const (
	defaultEarningBackfillInterval = 30 * time.Minute
	// How far back to look for paid orders that never earned.
	earningBackfillWindow = 72 * time.Hour
	// Orders looked at per run at most, so one run cannot run away.
	earningBackfillMaxOrders = 5000
)

type missingEarner interface {
	EarnMissing(ctx context.Context, since time.Time, maxOrders int) (checked, earned int, err error)
}

// EarningBackfillJob is the safety net behind earning at payment time
// (docs/prd-point-coin.md F3, PC-203). Every run it earns for orders paid in the last
// few days that should have earned and did not, for example because the database was
// briefly unreachable right after the payment committed.
type EarningBackfillJob struct {
	earner   missingEarner
	now      func() time.Time
	stopCh   chan struct{}
	stopOnce sync.Once
}

func NewEarningBackfillJob(earner missingEarner) *EarningBackfillJob {
	return &EarningBackfillJob{earner: earner, now: time.Now, stopCh: make(chan struct{})}
}

func (j *EarningBackfillJob) Start(interval time.Duration) {
	if interval <= 0 {
		interval = defaultEarningBackfillInterval
	}
	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("Earning backfill job started (interval: %s)", interval)
}

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

// RunOnce earns for every missed order in the window and reports how many it fixed.
// It is quiet when nothing was missed.
func (j *EarningBackfillJob) RunOnce(ctx context.Context) int {
	checked, earned, err := j.earner.EarnMissing(ctx, j.now().Add(-earningBackfillWindow), earningBackfillMaxOrders)
	if err != nil {
		logger.NonContext.Error("Earning backfill failed to run", err)
	}
	if earned > 0 {
		logger.NonContext.WarnWithFields("Earning backfill credited orders that had missed their earning",
			map[string]interface{}{"checked": checked, "earned": earned}, nil)
	}
	return earned
}