package ratelimit

import (
	"context"
	"sync"
	"time"
)

type Limiter struct {
	interval time.Duration

	mu   sync.Mutex
	next time.Time
}

func New(requestsPerMinute int) *Limiter {
	if requestsPerMinute <= 0 {
		return &Limiter{}
	}
	return &Limiter{interval: time.Minute / time.Duration(requestsPerMinute)}
}

func (l *Limiter) Wait(ctx context.Context) error {
	if l.interval <= 0 {
		return nil
	}

	l.mu.Lock()
	now := time.Now()
	if l.next.IsZero() {
		l.next = now.Add(l.interval)
		l.mu.Unlock()
		return nil
	}

	wake := l.next
	if now.After(wake) {
		l.next = now.Add(l.interval)
		l.mu.Unlock()
		return nil
	}
	l.next = l.next.Add(l.interval)
	l.mu.Unlock()

	timer := time.NewTimer(time.Until(wake))
	defer timer.Stop()

	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-timer.C:
		return nil
	}
}