package main

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"strings"
	"time"
)

const page = `<!doctype html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><meta name="robots" content="noindex"><title>Proxy Edge</title><style>body{margin:0;background:#0b1220;color:#dce7f7;font:16px system-ui,sans-serif}main{max-width:720px;margin:16vh auto;padding:32px}h1{font-size:42px;margin:0 0 12px;color:#fff}p{line-height:1.6;color:#9eb2cc}.badge{display:inline-block;padding:6px 10px;border:1px solid #274262;border-radius:999px;color:#86b7ea;font-size:13px}</style></head><body><main><span class="badge">Proxy Edge</span><h1>Private edge transport</h1><p>This endpoint provides resilient transport and availability services for authorized clients.</p></main></body></html>`

func requestHostname(hostport string) string {
	host := strings.TrimSpace(hostport)
	if parsed, _, err := net.SplitHostPort(host); err == nil {
		return strings.ToLower(parsed)
	}
	return strings.ToLower(strings.Trim(host, "[]"))
}

func main() {
	hostname := strings.ToLower(strings.TrimSpace(os.Getenv("TPROXY_HOSTNAME")))
	if hostname == "" {
		log.Fatal("TPROXY_HOSTNAME is required")
	}

	target, err := url.Parse("http://127.0.0.1:8080")
	if err != nil {
		log.Fatal(err)
	}

	proxy := &httputil.ReverseProxy{
		Rewrite: func(request *httputil.ProxyRequest) {
			request.SetURL(target)
			request.Out.Host = request.In.Host

			clientIP := strings.TrimSpace(request.In.Header.Get("X-Real-IP"))
			if net.ParseIP(clientIP) == nil {
				clientIP, _, _ = net.SplitHostPort(request.In.RemoteAddr)
			}
			request.Out.Header.Set("X-Real-IP", clientIP)
			request.Out.Header.Set("X-Forwarded-For", clientIP)
			if proto := request.In.Header.Get("X-Forwarded-Proto"); proto != "" {
				request.Out.Header.Set("X-Forwarded-Proto", proto)
			}
		},
		ErrorHandler: func(response http.ResponseWriter, _ *http.Request, proxyErr error) {
			log.Printf("relay error: %v", proxyErr)
			http.Error(response, "upstream unavailable", http.StatusBadGateway)
		},
	}

	handler := http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
		if requestHostname(request.Host) != hostname {
			http.Error(response, "misdirected request", http.StatusMisdirectedRequest)
			return
		}

		response.Header().Set("X-Content-Type-Options", "nosniff")
		response.Header().Set("Referrer-Policy", "no-referrer")

		staticPath := request.URL.Path == "/" ||
			request.URL.Path == "/about" ||
			request.URL.Path == "/privacy"
		if request.Method == http.MethodGet && request.URL.RawQuery == "" && staticPath {
			response.Header().Set("Content-Type", "text/html; charset=utf-8")
			response.Header().Set("Cache-Control", "public, max-age=300")
			_, _ = fmt.Fprint(response, page)
			return
		}

		proxy.ServeHTTP(response, request)
	})

	server := &http.Server{
		Addr:              ":8088",
		Handler:           handler,
		ReadHeaderTimeout: 10 * time.Second,
		IdleTimeout:       90 * time.Second,
	}

	log.Printf("ingress listening on %s for %s", server.Addr, hostname)
	log.Fatal(server.ListenAndServe())
}