package qq_obv11

// This file implements the sliding-window send rate limiter that keeps QQ
// OneBot proactive/reply traffic from bursting (see DevDocs/design/08 section
// 3, "注意风控").

import (
	"errors"
	"sync"
	"time"
)

// ErrRateLimited is returned by SendMessage/SendProactive when the configured
// per-window send quota is exhausted.
var ErrRateLimited = errors.New("qq-obv11: send rate limit exceeded")

// rateLimiter enforces a maximum number of events within a sliding window. It
// is disabled when max is non-positive.
type rateLimiter struct {
	max    int
	window time.Duration
	mu     sync.Mutex
	times  []time.Time
}

func newRateLimiter(max int, window time.Duration) *rateLimiter {
	return &rateLimiter{max: max, window: window}
}

// allow records a send at now and reports whether it fits within the window
// quota. A disabled limiter (max <= 0) always allows. The timestamp is only
// recorded when the send is accepted.
func (r *rateLimiter) allow(now time.Time) bool {
	if r == nil || r.max <= 0 {
		return true
	}
	r.mu.Lock()
	defer r.mu.Unlock()

	cutoff := now.Add(-r.window)
	i := 0
	for i < len(r.times) && !r.times[i].After(cutoff) {
		i++
	}
	r.times = r.times[i:]

	if len(r.times) >= r.max {
		return false
	}
	r.times = append(r.times, now)
	return true
}