package onionloc

import (
	"net/http"
	"strings"

	"golang.org/x/net/html"
)

const (
	HTTPHeaderName = "Onion-Location"
)

func HTTP(rsp *http.Response) (string, bool) {
	v, ok := rsp.Header[HTTPHeaderName]
	if !ok {
		return "", false
	}
	if len(v) != 1 {
		return "", false
	}
	return v[0], true
}

func HTML(rsp *http.Response) (string, bool) {
	z := html.NewTokenizer(rsp.Body)
	for {
		tt := z.Next()
		if tt == html.ErrorToken {
			return "", false // EOF and other errors
		}

		switch tt {
		case html.StartTagToken, html.SelfClosingTagToken:
			t := z.Token()

			// Looking for the html meta tag, see:
			// https://www.w3schools.com/tags/tag_meta.asp
			//
			// We expect two attributes: "key" and "content"
			if strings.ToLower(t.Data) != "meta" {
				break
			}
			if len(t.Attr) != 2 {
				break
			}

			// We're looking for the "http-equiv" key, see:
			// https://www.w3schools.com/tags/att_meta_http_equiv.asp
			//
			// In particular with the value "onion-location", see:
			// https://community.torproject.org/onion-services/advanced/onion-location/
			//
			// If we have all this and a following content
			// attribute, that is the Onion-Location URL that this
			// page advertises.  We make no attempt to validate
			// whether the content value is really an onion address.
			attr := t.Attr[0]
			if strings.ToLower(attr.Key) != "http-equiv" {
				break
			}
			if strings.ToLower(attr.Val) != "onion-location" {
				break
			}
			attr = t.Attr[1]
			if strings.ToLower(attr.Key) != "content" {
				break
			}

			return attr.Val, true
		default:
		}
	}
}