package api

import (
	"net"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

var (
	cachedLocalIPs   []string
	cachedLocalIPsAt time.Time
	cachedLocalIPsMu sync.Mutex
	localIPsCacheTTL = 30 * time.Second
)

type ServerInfo struct {
	Port                  int      `json:"port"`
	Host                  string   `json:"host"`
	LocalIPs              []string `json:"local_ips"`
	LANURL                string   `json:"lan_url"`
	TunnelURL             string   `json:"tunnel_url,omitempty"`
	CloudflaredConfigured bool     `json:"cloudflared_configured"`
	SuggestedURL          string   `json:"suggested_url"`
	DashboardURL          string   `json:"dashboard_url"`
	WebSocketURL          string   `json:"websocket_url"`
	Version               string   `json:"version,omitempty"`
}

// GetServerInfo returns URLs workers and droppers should use to reach this deck.
// When the dashboard is opened via HTTPS reverse proxy (e.g. Cloudflare tunnel),
// suggested_url uses https and omits :443 — not the local listen port (8989).
// lan_url is always the LAN http endpoint for workers on the same network.
func GetServerInfo(w http.ResponseWriter, r *http.Request, publicURLOverride string, listenPort int, cloudflaredConfigured bool, version ...string) {
	if listenPort <= 0 {
		listenPort = 8989
	}

	localIPs := listLocalIPv4Cached()
	lanURL := lanURLFromIPs(localIPs, listenPort)
	tunnelURL := tunnelURLFromRequest(r)
	suggestedURL := resolveSuggestedURL(r, publicURLOverride, listenPort, localIPs)

	host := r.Host
	port := listenPort
	if h, p, err := net.SplitHostPort(r.Host); err == nil {
		host = h
		if parsed := parsePort(p); parsed > 0 {
			port = parsed
		}
	}

	info := ServerInfo{
		Port:                  port,
		Host:                  host,
		LocalIPs:              localIPs,
		LANURL:                lanURL,
		TunnelURL:             tunnelURL,
		CloudflaredConfigured: cloudflaredConfigured,
		SuggestedURL:          suggestedURL,
		DashboardURL:          suggestedURL,
		WebSocketURL:          httpToWS(suggestedURL) + "/ws/agent",
	}
	if len(version) > 0 {
		info.Version = version[0]
	}

	writeJSON(w, info)
}

func lanURLFromIPs(localIPs []string, listenPort int) string {
	if len(localIPs) == 0 {
		return ""
	}
	return formatBaseURL("http", localIPs[0], listenPort)
}

func tunnelURLFromRequest(r *http.Request) string {
	scheme := requestScheme(r)
	if scheme != "https" {
		return ""
	}
	host := requestHost(r)
	hostOnly, port := hostAndPort(host, scheme)
	if isLoopbackHost(hostOnly) {
		return ""
	}
	return formatBaseURL(scheme, hostOnly, port)
}

func resolveSuggestedURL(r *http.Request, publicOverride string, listenPort int, localIPs []string) string {
	if norm := normalizePublicURL(publicOverride); norm != "" {
		return norm
	}
	return externalBaseFromRequest(r, listenPort, localIPs)
}

func externalBaseFromRequest(r *http.Request, listenPort int, localIPs []string) string {
	scheme := requestScheme(r)
	host := requestHost(r)
	hostOnly, port := hostAndPort(host, scheme)

	if isLoopbackHost(hostOnly) && len(localIPs) > 0 {
		hostOnly = localIPs[0]
		scheme = "http"
		port = listenPort
	}

	return formatBaseURL(scheme, hostOnly, port)
}

func requestScheme(r *http.Request) string {
	if r.TLS != nil {
		return "https"
	}
	if p := strings.TrimSpace(strings.Split(r.Header.Get("X-Forwarded-Proto"), ",")[0]); p != "" {
		return strings.ToLower(p)
	}
	return "http"
}

func requestHost(r *http.Request) string {
	if h := strings.TrimSpace(strings.Split(r.Header.Get("X-Forwarded-Host"), ",")[0]); h != "" {
		return h
	}
	return r.Host
}

func hostAndPort(host string, scheme string) (hostOnly string, port int) {
	if h, p, err := net.SplitHostPort(host); err == nil {
		return strings.Trim(h, "[]"), parsePort(p)
	}
	if strings.Count(host, ":") == 1 && !strings.Contains(host, "]") {
		parts := strings.SplitN(host, ":", 2)
		return parts[0], parsePort(parts[1])
	}
	hostOnly = strings.Trim(host, "[]")
	if scheme == "https" {
		return hostOnly, 443
	}
	return hostOnly, 80
}

func formatBaseURL(scheme, host string, port int) string {
	host = strings.Trim(host, "[]")
	if (scheme == "https" && port == 443) || (scheme == "http" && port == 80) {
		return scheme + "://" + host
	}
	return scheme + "://" + net.JoinHostPort(host, itoa(port))
}

func normalizePublicURL(raw string) string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return ""
	}
	u, err := url.Parse(raw)
	if err != nil || u.Scheme == "" || u.Host == "" {
		return strings.TrimRight(raw, "/")
	}
	_, port := hostAndPort(u.Host, u.Scheme)
	u.Host = formatURLHost(u.Hostname(), port, u.Scheme)
	u.Path = ""
	u.RawPath = ""
	u.RawQuery = ""
	u.Fragment = ""
	return strings.TrimRight(u.String(), "/")
}

func formatURLHost(hostname string, port int, scheme string) string {
	if (scheme == "https" && port == 443) || (scheme == "http" && port == 80) {
		return hostname
	}
	return net.JoinHostPort(hostname, itoa(port))
}

func httpToWS(base string) string {
	if strings.HasPrefix(base, "https://") {
		return "wss://" + strings.TrimPrefix(base, "https://")
	}
	return "ws://" + strings.TrimPrefix(base, "http://")
}

func listLocalIPv4Cached() []string {
	cachedLocalIPsMu.Lock()
	defer cachedLocalIPsMu.Unlock()
	if cachedLocalIPs != nil && time.Since(cachedLocalIPsAt) < localIPsCacheTTL {
		out := make([]string, len(cachedLocalIPs))
		copy(out, cachedLocalIPs)
		return out
	}
	cachedLocalIPs = listLocalIPv4()
	cachedLocalIPsAt = time.Now()
	out := make([]string, len(cachedLocalIPs))
	copy(out, cachedLocalIPs)
	return out
}

func listLocalIPv4() []string {
	var ips []string
	ifaces, err := net.Interfaces()
	if err != nil {
		return ips
	}
	for _, iface := range ifaces {
		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
			continue
		}
		addrs, err := iface.Addrs()
		if err != nil {
			continue
		}
		for _, addr := range addrs {
			var ip net.IP
			switch v := addr.(type) {
			case *net.IPNet:
				ip = v.IP
			case *net.IPAddr:
				ip = v.IP
			}
			if ip == nil || ip.IsLoopback() {
				continue
			}
			ip = ip.To4()
			if ip == nil {
				continue
			}
			ips = append(ips, ip.String())
		}
	}
	return ips
}

func isLoopbackHost(host string) bool {
	return host == "localhost" || host == "127.0.0.1" || host == "::1"
}

func parsePort(s string) int {
	n := 0
	for _, ch := range s {
		if ch < '0' || ch > '9' {
			return 8989
		}
		n = n*10 + int(ch-'0')
		if n > 65535 {
			return 8989
		}
	}
	if n == 0 {
		return 8989
	}
	return n
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	var buf [16]byte
	i := len(buf)
	for n > 0 {
		i--
		buf[i] = byte('0' + n%10)
		n /= 10
	}
	return string(buf[i:])
}