package middleware

import (
	"RenewCMS/api/pkg/apperr"
	"RenewCMS/api/pkg/claims"
	"net/http"
	"strconv"
	"sync"
	"time"
)

type rateLimitWindow struct {
	start time.Time
	count int
}

type rateLimitCounters struct {
	mu        sync.Mutex
	window    time.Duration
	windows   map[string]*rateLimitWindow
	lastSweep time.Time
}

func NewRateLimiter(maxAttempts int, window time.Duration) func(http.Handler) http.Handler {
	return newKeyedRateLimiter(maxAttempts, window, connectionHostKey)
}

func connectionHostKey(r *http.Request) string {
	return hostOf(r.RemoteAddr)
}

func NewUserRateLimiter(maxAttempts int, window time.Duration) func(http.Handler) http.Handler {
	return newKeyedRateLimiter(maxAttempts, window, userRateLimitKey)
}

func userRateLimitKey(r *http.Request) string {
	userId, _ := claims.UserId(r)
	return strconv.FormatUint(uint64(userId), 10)
}

func newKeyedRateLimiter(maxAttempts int, window time.Duration, keyOf func(*http.Request) string) func(http.Handler) http.Handler {
	counters := &rateLimitCounters{window: window, windows: make(map[string]*rateLimitWindow)}

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			retryAfter, allowed := counters.recordAttempt(keyOf(r), maxAttempts, time.Now())
			if !allowed {
				w.Header().Set("Retry-After", strconv.Itoa(retryAfter))
				http.Error(w, apperr.TooManyRequestsErrorMessage, http.StatusTooManyRequests)
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

func (c *rateLimitCounters) recordAttempt(key string, maxAttempts int, now time.Time) (int, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.sweepExpired(now)
	current, exists := c.windows[key]
	if !exists || now.Sub(current.start) >= c.window {
		current = &rateLimitWindow{start: now}
		c.windows[key] = current
	}

	current.count++
	if current.count > maxAttempts {
		return retryAfterSeconds(c.window - now.Sub(current.start)), false
	}
	return 0, true
}

func (c *rateLimitCounters) sweepExpired(now time.Time) {
	if now.Sub(c.lastSweep) < c.window {
		return
	}
	c.lastSweep = now
	for key, current := range c.windows {
		if now.Sub(current.start) >= c.window {
			delete(c.windows, key)
		}
	}
}

func retryAfterSeconds(remaining time.Duration) int {
	seconds := int(remaining / time.Second)
	if remaining%time.Second > 0 {
		seconds++
	}
	if seconds < 0 {
		return 0
	}
	return seconds
}