package service

import (
	"net/netip"
	"strings"
)

// DeviceKind 设备形态（前端据此选图标）
const (
	DeviceKindComputer = "computer"
	DeviceKindMobile   = "mobile"
	DeviceKindTablet   = "tablet"
)

// ParsedUA 从 User-Agent 抽出的可读设备信息
type ParsedUA struct {
	Kind    string // computer | mobile | tablet
	OS      string // Windows / macOS / Android / iOS / Linux
	Label   string // Windows 电脑 / Android 手机
	Browser string
}

// ParseUserAgent 轻量 UA 解析，覆盖常见桌面/移动浏览器，不引入第三方库。
func ParseUserAgent(ua string) ParsedUA {
	u := strings.TrimSpace(ua)
	if u == "" {
		return ParsedUA{Kind: DeviceKindComputer, OS: "未知", Label: "未知设备", Browser: "未知浏览器"}
	}
	low := strings.ToLower(u)

	kind, osName, label := classifyDevice(u, low)
	browser := classifyBrowser(u, low)
	return ParsedUA{Kind: kind, OS: osName, Label: label, Browser: browser}
}

func classifyDevice(u, low string) (kind, osName, label string) {
	hasAndroid := strings.Contains(low, "android")
	hasIPhone := strings.Contains(low, "iphone")
	hasIPad := strings.Contains(low, "ipad") || (strings.Contains(low, "macintosh") && strings.Contains(low, "mobile"))
	hasMobileToken := strings.Contains(low, "mobile") || strings.Contains(u, "Mobile")

	switch {
	case hasIPad:
		return DeviceKindTablet, "iOS", "iPad"
	case hasIPhone:
		return DeviceKindMobile, "iOS", "iOS 手机"
	case hasAndroid:
		if strings.Contains(low, "tablet") || !hasMobileToken {
			return DeviceKindTablet, "Android", "Android 平板"
		}
		return DeviceKindMobile, "Android", "Android 手机"
	case strings.Contains(low, "windows"):
		return DeviceKindComputer, "Windows", "Windows 电脑"
	case strings.Contains(low, "mac os") || strings.Contains(low, "macintosh"):
		return DeviceKindComputer, "macOS", "macOS 电脑"
	case strings.Contains(low, "cros"):
		return DeviceKindComputer, "ChromeOS", "ChromeOS 电脑"
	case strings.Contains(low, "linux"):
		return DeviceKindComputer, "Linux", "Linux 电脑"
	default:
		if hasMobileToken {
			return DeviceKindMobile, "未知", "手机"
		}
		return DeviceKindComputer, "未知", "电脑"
	}
}

func classifyBrowser(u, low string) string {
	switch {
	case strings.Contains(u, "MicroMessenger"):
		return "微信"
	case strings.Contains(low, "edg/") || strings.Contains(low, "edgios/") || strings.Contains(low, "edga/"):
		return "Microsoft Edge"
	case strings.Contains(low, "opr/") || strings.Contains(low, "opera"):
		return "Opera"
	case strings.Contains(low, "firefox/") || strings.Contains(low, "fxios/"):
		return "Firefox"
	case strings.Contains(low, "crios/"):
		return "Google Chrome"
	case strings.Contains(low, "chrome/") && !strings.Contains(low, "edg"):
		return "Google Chrome"
	case strings.Contains(low, "safari/") && !strings.Contains(low, "chrome") && !strings.Contains(low, "chromium"):
		return "Safari"
	default:
		return "未知浏览器"
	}
}

func uaFingerprint(p ParsedUA) string {
	return p.Kind + "|" + p.OS + "|" + p.Browser
}

func parseIPAddr(ip string) (netip.Addr, bool) {
	ip = strings.TrimSpace(ip)
	if ip == "" {
		return netip.Addr{}, false
	}
	if i := strings.IndexByte(ip, '%'); i >= 0 {
		ip = ip[:i]
	}
	addr, err := netip.ParseAddr(ip)
	if err != nil {
		return netip.Addr{}, false
	}
	return addr.Unmap(), true
}

// canonicalIP 归一化 IP：IPv4-mapped 解开；本机 ::1 / 127.0.0.1 视为同一地址。
func canonicalIP(ip string) string {
	addr, ok := parseIPAddr(ip)
	if !ok {
		return strings.TrimSpace(ip)
	}
	if addr.IsLoopback() {
		return "127.0.0.1"
	}
	return addr.String()
}

func deviceFingerprint(ip, ua string) string {
	return canonicalIP(ip) + "|" + uaFingerprint(ParseUserAgent(ua))
}