package middleware

import (
	"fmt"
	"strconv"
	"strings"
	"time"

	"github.com/gogf/gf/v2/errors/gerror"
	"github.com/gogf/gf/v2/net/ghttp"

	"easygoadmin/internal/consts"
	"easygoadmin/utility/cache"
	"easygoadmin/utility/response"
)

// ============================== API 限流中间件 ==============================
//
// 固定窗口计数：键按窗口起点对齐（ratelimit:{ip}:{path}:{窗口起点}），
// 计数存 utility/cache（Redis 优先、内存降级），多实例部署时共享计数。
//
// 规则：
//   - 仅限 /api/ 前缀接口；文档（/api.json）、静态资源、健康检查不受限
//   - 认证入口（登录/验证码/令牌兑换）按 rateLimit.authLimit 单独更严阈值
//   - 计数存储异常时放行（限流不阻断业务）

// RateLimit API 限流
func RateLimit(r *ghttp.Request) {
	if !cfgBool(r.Context(), "rateLimit.enable", true) {
		r.Middleware.Next()
		return
	}
	path := r.URL.Path
	if !isRateLimitedPath(path) {
		r.Middleware.Next()
		return
	}
	window := cfgInt(r.Context(), "rateLimit.windowSeconds", 60)
	limit := cfgInt(r.Context(), "rateLimit.limit", 120)
	if isAuthPath(path) {
		limit = cfgInt(r.Context(), "rateLimit.authLimit", 10)
	}
	if limit <= 0 || window <= 0 {
		r.Middleware.Next()
		return
	}

	// 窗口起点对齐：同一窗口内共享计数键
	windowStart := time.Now().Unix() / int64(window) * int64(window)
	key := fmt.Sprintf("ratelimit:%s:%s:%d", realClientIP(r), path, windowStart)
	n, err := incrCounter(r, key, window)
	if err != nil {
		r.Middleware.Next()
		return
	}
	if n > int64(limit) {
		response.Write(r, response.Fail(gerror.NewCode(consts.CodeTooManyRequests)))
		return
	}
	r.Middleware.Next()
}

// isRateLimitedPath 判断是否为参与限流的接口路径
// /api.json 与 /swagger 不带 /api/ 前缀，自然排除；健康检查显式豁免
func isRateLimitedPath(path string) bool {
	if path == "/api/health" {
		return false
	}
	return path == "/api" || strings.HasPrefix(path, "/api/")
}

// isAuthPath 判断是否为认证入口（适用更严格的独立阈值）
func isAuthPath(path string) bool {
	switch path {
	case "/api/login", "/api/captcha", "/api/oauth2/token":
		return true
	}
	return false
}

// incrCounter 固定窗口计数自增
// 键已含窗口起点，TTL 仅用于回收存储，续期不影响窗口归属
func incrCounter(r *ghttp.Request, key string, windowSeconds int) (int64, error) {
	ttl := windowSeconds + 5
	if raw, ok := cache.Get(r.Context(), key); ok {
		n, _ := strconv.ParseInt(raw, 10, 64)
		n++
		_ = cache.Set(r.Context(), key, strconv.FormatInt(n, 10), ttl)
		return n, nil
	}
	if cache.SetNX(r.Context(), key, "1", ttl) {
		return 1, nil
	}
	// 并发下 SetNX 未抢到：读现值再加一
	if raw, ok := cache.Get(r.Context(), key); ok {
		n, _ := strconv.ParseInt(raw, 10, 64)
		n++
		_ = cache.Set(r.Context(), key, strconv.FormatInt(n, 10), ttl)
		return n, nil
	}
	return 1, nil
}