package handler

import (
	"net"
	"strings"

	"github.com/gin-gonic/gin"
)

// resolveVisitorIP 优先信任反代头，回落到 Gin ClientIP。
func resolveVisitorIP(c *gin.Context) string {
	candidates := []string{
		c.GetHeader("CF-Connecting-IP"),
		c.GetHeader("True-Client-IP"),
		c.GetHeader("X-Real-IP"),
	}
	if xff := c.GetHeader("X-Forwarded-For"); xff != "" {
		// 取最左侧第一个非空 IP
		for _, part := range strings.Split(xff, ",") {
			part = strings.TrimSpace(part)
			if part != "" {
				candidates = append(candidates, part)
				break
			}
		}
	}
	for _, raw := range candidates {
		ip := strings.TrimSpace(raw)
		if ip == "" {
			continue
		}
		// 去掉端口
		if host, _, err := net.SplitHostPort(ip); err == nil {
			ip = host
		}
		if net.ParseIP(ip) != nil {
			return ip
		}
	}
	ip := c.ClientIP()
	if host, _, err := net.SplitHostPort(ip); err == nil {
		return host
	}
	return ip
}

// resolveVisitorRegion 基于 IP 与常见 CDN 国家头做粗粒度地区，无需第三方库。
// 私网/本机显示「内网」；有国家头则映射中文名；否则「未知」。
func resolveVisitorRegion(c *gin.Context, ip string) string {
	// Cloudflare / 部分网关国家码
	country := strings.ToUpper(strings.TrimSpace(c.GetHeader("CF-IPCountry")))
	if country == "" {
		country = strings.ToUpper(strings.TrimSpace(c.GetHeader("X-AppEngine-Country")))
	}
	if country == "" {
		country = strings.ToUpper(strings.TrimSpace(c.GetHeader("CloudFront-Viewer-Country")))
	}
	if country != "" && country != "XX" && country != "T1" {
		if name, ok := countryNameCN(country); ok {
			return name
		}
		return country
	}

	parsed := net.ParseIP(ip)
	if parsed == nil {
		return "未知"
	}
	if parsed.IsLoopback() || parsed.IsPrivate() || parsed.IsLinkLocalUnicast() || parsed.IsLinkLocalMulticast() {
		return "内网"
	}
	// 未接入 GeoIP 库时，公网 IP 地区暂标未知（可后续接入离线库）
	return "未知"
}

func countryNameCN(code string) (string, bool) {
	names := map[string]string{
		"CN": "中国", "HK": "中国香港", "MO": "中国澳门", "TW": "中国台湾",
		"US": "美国", "JP": "日本", "KR": "韩国", "SG": "新加坡",
		"GB": "英国", "DE": "德国", "FR": "法国", "AU": "澳大利亚",
		"CA": "加拿大", "RU": "俄罗斯", "IN": "印度", "BR": "巴西",
		"MY": "马来西亚", "TH": "泰国", "VN": "越南", "PH": "菲律宾",
		"ID": "印度尼西亚", "AE": "阿联酋", "SA": "沙特阿拉伯",
	}
	name, ok := names[code]
	return name, ok
}

// summarizeUserAgent 将 UA 压缩为可读设备摘要，如 "Chrome / macOS"。
func summarizeUserAgent(ua string) string {
	ua = strings.TrimSpace(ua)
	if ua == "" {
		return ""
	}
	browser := "浏览器"
	osName := "未知系统"
	switch {
	case strings.Contains(ua, "Edg/"):
		browser = "Edge"
	case strings.Contains(ua, "Chrome/") && !strings.Contains(ua, "Edg/"):
		browser = "Chrome"
	case strings.Contains(ua, "Firefox/"):
		browser = "Firefox"
	case strings.Contains(ua, "Safari/") && !strings.Contains(ua, "Chrome/"):
		browser = "Safari"
	case strings.Contains(ua, "MicroMessenger"):
		browser = "微信"
	}
	switch {
	case strings.Contains(ua, "Windows"):
		osName = "Windows"
	case strings.Contains(ua, "Mac OS X") || strings.Contains(ua, "Macintosh"):
		osName = "macOS"
	case strings.Contains(ua, "Android"):
		osName = "Android"
	case strings.Contains(ua, "iPhone") || strings.Contains(ua, "iPad"):
		osName = "iOS"
	case strings.Contains(ua, "Linux"):
		osName = "Linux"
	}
	return browser + " / " + osName
}

func captureVisitorMeta(c *gin.Context) (ip, region, ua, device string) {
	ip = resolveVisitorIP(c)
	region = resolveVisitorRegion(c, ip)
	ua = c.Request.UserAgent()
	if len(ua) > 500 {
		ua = ua[:500]
	}
	device = summarizeUserAgent(ua)
	return
}