package useragent

import (
	"fmt"
	"net/http"
	"net/url"
	"regexp"
	"strings"

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

const DefaultVer = "1.0.0"

// Info 与前端 X-User-Agent 字段对齐，供 SSR 组装上游请求头。
type Info struct {
	RawUA         string
	DevType       string
	SysType       string
	Ver           string
	BuildID       string
	DeviceBrand   string
	DeviceModel   string
	SystemName    string
	SystemVersion string
	SID           string
}

// BuildOptions SSR / 代理侧可选覆盖项。
type BuildOptions struct {
	Ver string
	SID string
	// RawUA 为空时从 Request.UserAgent 读取
	RawUA string
}

var (
	reIOSVer      = regexp.MustCompile(`OS (\d+[_\d]*) like Mac OS X`)
	reAndroidVer  = regexp.MustCompile(`Android ([\d.]+)`)
	reAndroidModel = regexp.MustCompile(`Android\s+[\d.]+;\s*([^;)]+?)(?:\s+Build\/|\))`)
	reWinNT       = regexp.MustCompile(`Windows NT ([\d.]+)`)
	reMacVer      = regexp.MustCompile(`Mac OS X ([\d_]+)`)
	reEdge        = regexp.MustCompile(`(?i)Edg/([\d.]+)`)
	reOpera       = regexp.MustCompile(`(?i)(?:OPR|Opera)/([\d.]+)`)
	reChrome      = regexp.MustCompile(`(?i)Chrome/([\d.]+)`)
	reSafari      = regexp.MustCompile(`(?i)Version/([\d.]+).*Safari`)
	reFirefox     = regexp.MustCompile(`(?i)Firefox/([\d.]+)`)
	reIE          = regexp.MustCompile(`(?i)(?:MSIE\s|Trident.*rv:)([\d.]+)`)
)

// ParseDeviceFromUA 从浏览器原生 User-Agent 解析设备信息（服务端无 navigator）。
func ParseDeviceFromUA(ua string) (brand, model, deviceType, systemName, systemVersion string) {
	ua = strings.TrimSpace(ua)
	switch {
	case strings.Contains(ua, "iPhone") || strings.Contains(ua, "iPad") || strings.Contains(ua, "iPod"):
		systemName = "iOS"
		brand = "Apple"
		if m := reIOSVer.FindStringSubmatch(ua); len(m) > 1 {
			systemVersion = strings.ReplaceAll(m[1], "_", ".")
		}
		switch {
		case strings.Contains(ua, "iPad"):
			model, deviceType = "iPad", "tablet"
		case strings.Contains(ua, "iPod"):
			model, deviceType = "iPod", "mobile"
		default:
			model, deviceType = "iPhone", "mobile"
		}
	case strings.Contains(ua, "Android"):
		systemName = "Android"
		if m := reAndroidVer.FindStringSubmatch(ua); len(m) > 1 {
			systemVersion = m[1]
		}
		if m := reAndroidModel.FindStringSubmatch(ua); len(m) > 1 {
			model = strings.TrimSpace(m[1])
		}
		brand = guessAndroidBrand(model, ua)
		if strings.Contains(ua, "Mobile") {
			deviceType = "mobile"
		} else {
			deviceType = "tablet"
		}
	case strings.Contains(ua, "Windows"):
		systemName = "Windows"
		deviceType = "desktop"
		if m := reWinNT.FindStringSubmatch(ua); len(m) > 1 {
			systemVersion = m[1]
		}
	case strings.Contains(ua, "Mac OS X") || strings.Contains(ua, "Macintosh"):
		systemName = "macOS"
		brand = "Apple"
		model = "Mac"
		deviceType = "desktop"
		if m := reMacVer.FindStringSubmatch(ua); len(m) > 1 {
			systemVersion = strings.ReplaceAll(m[1], "_", ".")
		}
	case strings.Contains(ua, "Linux"):
		systemName = "Linux"
		deviceType = "desktop"
	default:
		systemName = "Other"
		deviceType = "desktop"
	}
	return
}

func guessAndroidBrand(model, ua string) string {
	s := model + " " + ua
	rules := []struct {
		re    *regexp.Regexp
		brand string
	}{
		{regexp.MustCompile(`(?i)Build/HONOR|\bHONOR\b`), "Honor"},
		{regexp.MustCompile(`(?i)Build/HUAWEI|HUAWEI|HW-`), "Huawei"},
		{regexp.MustCompile(`(?i)SM-|samsung|Galaxy`), "Samsung"},
		{regexp.MustCompile(`(?i)Pixel`), "Google"},
		{regexp.MustCompile(`(?i)Redmi|POCO|XiaoMi|\bMi\b`), "Xiaomi"},
		{regexp.MustCompile(`(?i)OPPO|\bCPH\d{3,4}`), "OPPO"},
		{regexp.MustCompile(`(?i)vivo|\bV\d{4}`), "vivo"},
		{regexp.MustCompile(`(?i)OnePlus|ONEPLUS`), "OnePlus"},
		{regexp.MustCompile(`(?i)realme|\bRMX\d{3,4}`), "realme"},
	}
	for _, r := range rules {
		if r.re.MatchString(s) {
			return r.brand
		}
	}
	return ""
}

func detectSysType(ua string) string {
	uaLower := strings.ToLower(ua)
	switch {
	case strings.Contains(uaLower, "android"):
		return "h5_android"
	case strings.Contains(uaLower, "iphone"), strings.Contains(uaLower, "ipad"), strings.Contains(uaLower, "ipod"):
		return "h5_ios"
	default:
		return "h5_pc"
	}
}

func parseBrowser(ua string) (name, version string) {
	switch {
	case reEdge.MatchString(ua):
		m := reEdge.FindStringSubmatch(ua)
		return "Edge", m[1]
	case reOpera.MatchString(ua):
		m := reOpera.FindStringSubmatch(ua)
		return "Opera", m[1]
	case reChrome.MatchString(ua) && !reEdge.MatchString(ua):
		m := reChrome.FindStringSubmatch(ua)
		return "Chrome", m[1]
	case reSafari.MatchString(ua):
		m := reSafari.FindStringSubmatch(ua)
		return "Safari", m[1]
	case reFirefox.MatchString(ua):
		m := reFirefox.FindStringSubmatch(ua)
		return "Firefox", m[1]
	case reIE.MatchString(ua):
		m := reIE.FindStringSubmatch(ua)
		return "IE", m[1]
	default:
		return "", ""
	}
}

func buildDevType(brand, model, deviceType string) string {
	parts := make([]string, 0, 3)
	for _, v := range []string{brand, model, deviceType} {
		v = strings.TrimSpace(v)
		if v != "" {
			parts = append(parts, v)
		}
	}
	if len(parts) < 3 {
		return "Apple iPhone mobile"
	}
	return strings.Join(parts, " ")
}

// BuildInfo 根据原始 UA 组装结构化信息。
func BuildInfo(opts BuildOptions) Info {
	ua := strings.TrimSpace(opts.RawUA)
	ver := strings.TrimSpace(opts.Ver)
	if ver == "" {
		ver = DefaultVer
	}
	brand, model, deviceType, systemName, systemVersion := ParseDeviceFromUA(ua)
	browserName, browserVer := parseBrowser(ua)
	buildID := strings.TrimSpace(strings.TrimSpace(browserName + " " + browserVer))

	return Info{
		RawUA:         ua,
		DevType:       buildDevType(brand, model, deviceType),
		SysType:       detectSysType(ua),
		Ver:           ver,
		BuildID:       buildID,
		DeviceBrand:   brand,
		DeviceModel:   model,
		SystemName:    systemName,
		SystemVersion: systemVersion,
		SID:           strings.TrimSpace(opts.SID),
	}
}

// String 输出 X-User-Agent Header 值。
func (info Info) String() string {
	return fmt.Sprintf(
		"DevType=%s;SysType=%s;Ver=%s;BuildID=%s;device_brand=%s;device_model=%s;system_name=%s;system_version=%s;sid=%s",
		info.DevType,
		info.SysType,
		info.Ver,
		info.BuildID,
		info.DeviceBrand,
		info.DeviceModel,
		info.SystemName,
		info.SystemVersion,
		info.SID,
	)
}

// BuildXUserAgent 直接返回 Header 字符串。
func BuildXUserAgent(opts BuildOptions) string {
	return BuildInfo(opts).String()
}

// SIDFromRequest 从 cookie 读取 sid（与前端约定：sid / _s_token_）。
func SIDFromRequest(r *http.Request) string {
	if r == nil {
		return ""
	}
	if c, err := r.Cookie("sid"); err == nil && c != nil {
		if v := strings.TrimSpace(c.Value); v != "" {
			return v
		}
	}
	if c, err := r.Cookie("_s_token_"); err == nil && c != nil {
		v := strings.TrimSpace(c.Value)
		// 可能是 JSON：{"sid":"..."} 或纯字符串
		if strings.HasPrefix(v, "{") {
			const key = `"sid"`
			if i := strings.Index(v, key); i >= 0 {
				rest := v[i+len(key):]
				if j := strings.Index(rest, `"`); j >= 0 {
					rest = rest[j+1:]
					if k := strings.Index(rest, `"`); k >= 0 {
						return rest[:k]
					}
				}
			}
		}
		return v
	}
	return ""
}

// BuildXUserAgentFromRequest 供 SSR 反向代理上游 API 使用。
// 优先透传客户端已带的 X-User-Agent；否则用浏览器 UA 组装。
func BuildXUserAgentFromRequest(c *gin.Context, ver string) string {
	if c == nil || c.Request == nil {
		return BuildXUserAgent(BuildOptions{Ver: ver})
	}
	if xua := strings.TrimSpace(c.GetHeader("X-User-Agent")); xua != "" {
		return xua
	}
	return BuildXUserAgent(BuildOptions{
		Ver:   ver,
		SID:   SIDFromRequest(c.Request),
		RawUA: c.Request.UserAgent(),
	})
}

// TokenFromRequest 从 cookie 读取登录 token（与前端约定：token / _token_）。
func TokenFromRequest(r *http.Request) string {
	if r == nil {
		return ""
	}
	for _, name := range []string{"token", "_token_"} {
		if c, err := r.Cookie(name); err == nil && c != nil {
			if v := cookieUnescape(c.Value); v != "" {
				return v
			}
		}
	}
	return ""
}

func cookieUnescape(raw string) string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return ""
	}
	if decoded, err := url.QueryUnescape(raw); err == nil {
		return strings.TrimSpace(decoded)
	}
	return raw
}

// ClientIPFromRequest 优先透传已有 X-Real-IP / X-Forwarded-For，否则用远端地址。
func ClientIPFromRequest(c *gin.Context) string {
	if c == nil || c.Request == nil {
		return ""
	}
	if ip := strings.TrimSpace(c.GetHeader("X-Real-IP")); ip != "" {
		return ip
	}
	if xff := strings.TrimSpace(c.GetHeader("X-Forwarded-For")); xff != "" {
		if i := strings.Index(xff, ","); i >= 0 {
			return strings.TrimSpace(xff[:i])
		}
		return xff
	}
	return strings.TrimSpace(c.ClientIP())
}

// BuildUpstreamHeader 组装上游 API 请求头：X-Real-IP、User-Agent、X-User-Agent。
// 登录 token / sid 已在 cookie 中时由调用方按需写入 Authorization 等字段。
func BuildUpstreamHeader(c *gin.Context, ver string) map[string]string {
	header := make(map[string]string, 8)
	ApplyToHeader(header, c, ver)
	return header
}

// ApplyToHeader 将上游必需头写入 header map：
// X-Real-IP、User-Agent、X-User-Agent。
func ApplyToHeader(header map[string]string, c *gin.Context, ver string) {
	if header == nil {
		return
	}
	if c != nil && c.Request != nil {
		if ip := ClientIPFromRequest(c); ip != "" {
			header["X-Real-IP"] = ip
		}
		if ua := strings.TrimSpace(c.Request.UserAgent()); ua != "" {
			header["User-Agent"] = ua
		}
	}
	header["X-User-Agent"] = BuildXUserAgentFromRequest(c, ver)
}