package builder

import (
	"bytes"
	"fmt"
	"golang.org/x/net/html"
	"io"
)

func BodyAnchors(masked []byte) ([2]int, error) {
	var anchors [2]int
	opens, closes, offset := 0, 0, 0
	z := html.NewTokenizer(bytes.NewReader(masked))
	for {
		kind := z.Next()
		raw := z.Raw()
		start := offset
		offset += len(raw)
		switch kind {
		case html.ErrorToken:
			if z.Err() != io.EOF {
				return anchors, z.Err()
			}
			if opens != 1 || closes != 1 || anchors[0] >= anchors[1] {
				return anchors, fmt.Errorf("expected exactly one static body start and end")
			}
			return anchors, nil
		case html.StartTagToken:
			tag, _ := z.TagName()
			if bytes.Equal(tag, []byte("body")) {
				opens++
				anchors[0] = offset
			}
		case html.EndTagToken:
			tag, _ := z.TagName()
			if bytes.Equal(tag, []byte("body")) {
				closes++
				anchors[1] = start
			}
		}
	}
}