package calls

import (
	"sync"
	"time"
)

// budget is a sliding-window counter: at most limit events per key per
// window. It counts attempts, refused or not, because the point is to
// keep outsider traffic away from rastrillo's shared limiter (spec
// §3.2), and an attempt that reaches Begin is what consumes that. The
// budgets are process-local and reset on every deploy or restart.
type budget struct {
	mu     sync.Mutex
	limit  int
	window time.Duration
	hits   map[string][]time.Time
}

func newBudget(limit int, window time.Duration) *budget {
	return &budget{limit: limit, window: window, hits: map[string][]time.Time{}}
}

// allow records an attempt and reports whether it was within budget.
func (b *budget) allow(key string, now time.Time) bool {
	b.mu.Lock()
	defer b.mu.Unlock()
	cut := now.Add(-b.window)
	kept := b.hits[key][:0]
	for _, t := range b.hits[key] {
		if t.After(cut) {
			kept = append(kept, t)
		}
	}
	if len(kept) == 0 {
		delete(b.hits, key)
	} else {
		b.hits[key] = kept
	}
	if len(kept) >= b.limit {
		return false
	}
	b.hits[key] = append(kept, now)
	return true
}