package main

import (
	"fmt"
	"log"
	"net"
	"net/http"
	"os"
	"strings"
)

var (
	name            string
	RemoteIPHeaders = []string{"X-Forwarded-For", "X-Real-IP"}
)

func main() {
	hostname, err := os.Hostname()
	if err != nil {
		log.Println("got hostname error:", err)
	}

	name = hostname

	http.HandleFunc("/echo", echoHandler)

	fmt.Println("Starting server on :8080")
	if err := http.ListenAndServe(":8080", nil); err != nil {
		log.Fatal(err)
	}

}

func echoHandler(w http.ResponseWriter, r *http.Request) {
	clientIp := getRemoteIP(r)

	log.Printf("client %s connected\n\n", clientIp)
	fmt.Fprintf(w, "hello %s, Host %s provides services\n", clientIp, name)
}

func getRemoteIP(r *http.Request) string {
	for k, v := range r.Header {
		fmt.Printf("KEY=%s VALUE=%v\n", k, v)
	}

	for _, headerName := range RemoteIPHeaders {
		ip, valid := validateHeader(r.Header.Get(headerName))
		if valid {
			return ip
		}
	}

	return RemoteIP(r)
}

func validateHeader(header string) (clientIP string, valid bool) {
	if header == "" {
		return "", false
	}
	items := strings.Split(header, ",")
	for i := len(items) - 1; i >= 0; i-- {
		ipStr := strings.TrimSpace(items[i])
		ip := net.ParseIP(ipStr)
		if ip == nil {
			break
		}

		if i == 0 {
			return ipStr, true
		}

		// // X-Forwarded-For is appended by proxy
		// // Check IPs in reverse order and stop when find untrusted proxy
		// if (i == 0) || (!engine.isTrustedProxy(ip)) {
		// 	return ipStr, true
		// }
	}
	return "", false
}

func RemoteIP(r *http.Request) string {
	ip, _, err := net.SplitHostPort(strings.TrimSpace(r.RemoteAddr))
	if err != nil {
		return ""
	}

	return ip
}