package server

import (
	"sync"
	"time"
)

// Simple token bucket keyed by arbitrary string. Thread-safe.
type bucket struct {
	tokens  float64
	lastRef time.Time
}

type RateLimiter struct {
	mu       sync.Mutex
	buckets  map[string]*bucket
	capacity float64
	refill   float64 // tokens per second
}

// NewRateLimiter: e.g. capacity=5, per=10min → 5 tokens, refilled at 5/600 tokens/sec.
func NewRateLimiter(capacity int, per time.Duration) *RateLimiter {
	return &RateLimiter{
		buckets:  map[string]*bucket{},
		capacity: float64(capacity),
		refill:   float64(capacity) / per.Seconds(),
	}
}

// Allow returns true if the key has a token to spend.
func (l *RateLimiter) Allow(key string) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	b, ok := l.buckets[key]
	now := time.Now()
	if !ok {
		b = &bucket{tokens: l.capacity, lastRef: now}
		l.buckets[key] = b
	}
	elapsed := now.Sub(b.lastRef).Seconds()
	b.tokens = minF(l.capacity, b.tokens+elapsed*l.refill)
	b.lastRef = now
	if b.tokens >= 1 {
		b.tokens--
		return true
	}
	return false
}

func minF(a, b float64) float64 {
	if a < b {
		return a
	}
	return b
}