package email

import (
	"sync"
	"time"
)

// slidingLimiter is an in-process email send budget (per key).
// Not shared across API replicas; RATE_LIMIT_REPLICAS does not divide this limiter.
// Multi-replica hard caps need edge/WAF (or a future shared store).
type slidingLimiter struct {
	mu     sync.Mutex
	window time.Duration
	limit  int
	hits   map[string][]time.Time
	lastGC time.Time
}

func newSlidingLimiter(limit int, window time.Duration) *slidingLimiter {
	if limit <= 0 {
		limit = 30
	}
	if window <= 0 {
		window = time.Minute
	}
	return &slidingLimiter{
		window: window,
		limit:  limit,
		hits:   make(map[string][]time.Time),
		lastGC: time.Now(),
	}
}

func (l *slidingLimiter) allow(key string) bool {
	now := time.Now()
	cutoff := now.Add(-l.window)
	l.mu.Lock()
	defer l.mu.Unlock()
	if now.Sub(l.lastGC) > l.window {
		for k, ts := range l.hits {
			kept := ts[:0]
			for _, t := range ts {
				if t.After(cutoff) {
					kept = append(kept, t)
				}
			}
			if len(kept) == 0 {
				delete(l.hits, k)
			} else {
				l.hits[k] = kept
			}
		}
		l.lastGC = now
	}
	ts := l.hits[key]
	kept := ts[:0]
	for _, t := range ts {
		if t.After(cutoff) {
			kept = append(kept, t)
		}
	}
	if len(kept) >= l.limit {
		l.hits[key] = kept
		return false
	}
	l.hits[key] = append(kept, now)
	return true
}