package main

import (
	"net"
	"net/http"
	"strings"
	"sync"
	"time"
)

type limiter struct {
	mu     sync.Mutex
	hits   map[string][]time.Time
	max    int
	window time.Duration
}

func newLimiter(max int, window time.Duration) *limiter {
	return &limiter{hits: map[string][]time.Time{}, max: max, window: window}
}

func (l *limiter) allow(key string) bool {
	l.mu.Lock()
	defer l.mu.Unlock()
	now := time.Now()
	cutoff := now.Add(-l.window)
	kept := l.hits[key][:0]
	for _, t := range l.hits[key] {
		if t.After(cutoff) {
			kept = append(kept, t)
		}
	}
	if len(kept) >= l.max {
		l.hits[key] = kept
		return false
	}
	l.hits[key] = append(kept, now)
	if len(l.hits) > 10000 {
		for k, v := range l.hits {
			if len(v) == 0 || !v[len(v)-1].After(cutoff) {
				delete(l.hits, k)
			}
		}
	}
	return true
}

func clientIP(r *http.Request) string {
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		first, _, _ := strings.Cut(xff, ",")
		return strings.TrimSpace(first)
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}