package main

import (
	"fmt"
	"io"
	"log"
	"net/http"
	"regexp"
	"strings"
)

const port = "8280"

var emailRegex = regexp.MustCompile(`(?i)<EMailAddress>([^<]+)</EMailAddress>`)

func main() {
	http.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprint(w, "OK")
	})

	http.HandleFunc("/autodiscover/autodiscover.xml", handleAutodiscover)
	// Outlook sendet manchmal mit Großbuchstaben
	http.HandleFunc("/Autodiscover/Autodiscover.xml", handleAutodiscover)
	http.HandleFunc("/AutoDiscover/AutoDiscover.xml", handleAutodiscover)

	log.Printf("[autodiscover] Listening on port %s", port)
	if err := http.ListenAndServe(":"+port, nil); err != nil {
		log.Fatal(err)
	}
}

func handleAutodiscover(w http.ResponseWriter, r *http.Request) {
	var email string

	if r.Method == http.MethodPost {
		body, err := io.ReadAll(r.Body)
		if err == nil {
			if match := emailRegex.FindStringSubmatch(string(body)); len(match) > 1 {
				email = strings.TrimSpace(match[1])
			}
		}
		r.Body.Close()
	}

	var domain string
	if email != "" {
		parts := strings.SplitN(email, "@", 2)
		if len(parts) == 2 {
			domain = parts[1]
		}
	}
	if domain == "" {
		domain = extractDomainFromHost(r.Host)
	}

	log.Printf("[autodiscover] %s from %s - email=%q domain=%s", r.Method, r.RemoteAddr, email, domain)

	w.Header().Set("Content-Type", "application/xml")
	w.WriteHeader(http.StatusOK)
	fmt.Fprint(w, buildResponse(domain, email))
}

func extractDomainFromHost(host string) string {
	// Strip port
	if idx := strings.Index(host, ":"); idx >= 0 {
		host = host[:idx]
	}
	parts := strings.Split(host, ".")
	if len(parts) >= 3 && strings.EqualFold(parts[0], "autodiscover") {
		return strings.Join(parts[1:], ".")
	}
	if len(parts) >= 2 {
		return strings.Join(parts[len(parts)-2:], ".")
	}
	return host
}

func buildResponse(domain, loginName string) string {
	return fmt.Sprintf(`<?xml version="1.0" encoding="utf-8"?>
<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006">
  <Response xmlns="http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a">
    <Account>
      <AccountType>email</AccountType>
      <Action>settings</Action>
      <Protocol>
        <Type>IMAP</Type>
        <Server>imap.%s</Server>
        <Port>993</Port>
        <DomainRequired>off</DomainRequired>
        <LoginName>%s</LoginName>
        <SPA>off</SPA>
        <SSL>on</SSL>
        <AuthRequired>on</AuthRequired>
      </Protocol>
      <Protocol>
        <Type>SMTP</Type>
        <Server>smtp.%s</Server>
        <Port>465</Port>
        <DomainRequired>off</DomainRequired>
        <LoginName>%s</LoginName>
        <SPA>off</SPA>
        <SSL>on</SSL>
        <AuthRequired>on</AuthRequired>
      </Protocol>
    </Account>
  </Response>
</Autodiscover>`, domain, loginName, domain, loginName)
}