package main

import (
	"encoding/xml"
	"fmt"
	"net/http"
	"strings"
)

// findPrincipal asks the endpoint who we are.
//
// go-webdav does this too, but it resolves the request path with
// path.Join, which drops a trailing slash: a client pointed at /dav/
// ends up asking about /dav, and Cyrus answers 405 for that exact
// spelling while answering 207 for /dav/. Deeper paths tolerate either,
// so only this first request needs doing by hand.
func findPrincipal(endpoint, user, pass string) (string, error) {
	body := `<?xml version="1.0" encoding="utf-8"?>` +
		`<d:propfind xmlns:d="DAV:"><d:prop><d:current-user-principal/></d:prop></d:propfind>`

	req, err := http.NewRequest("PROPFIND", endpoint, strings.NewReader(body))
	if err != nil {
		return "", err
	}
	req.Header.Set("Depth", "0")
	req.Header.Set("Content-Type", "application/xml; charset=utf-8")
	req.SetBasicAuth(user, pass)

	resp, err := client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusMultiStatus {
		return "", fmt.Errorf("%s: %s", endpoint, resp.Status)
	}

	// Spelled out rather than using encoding/xml's "a>b" path
	// shorthand, which does not carry namespaces through.
	type href struct {
		Href string `xml:"DAV: href"`
	}
	type prop struct {
		Principal href `xml:"DAV: current-user-principal"`
	}
	type propstat struct {
		Prop prop `xml:"DAV: prop"`
	}
	type response struct {
		Propstats []propstat `xml:"DAV: propstat"`
	}
	var ms struct {
		Responses []response `xml:"DAV: response"`
	}
	if err := xml.NewDecoder(resp.Body).Decode(&ms); err != nil {
		return "", err
	}
	for _, r := range ms.Responses {
		for _, ps := range r.Propstats {
			if h := strings.TrimSpace(ps.Prop.Principal.Href); h != "" {
				return h, nil
			}
		}
	}
	return "", fmt.Errorf("%s: no current-user-principal", endpoint)
}