package classes

import (
	"bytes"
	"strings"

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

// ConvertH1 turns every h1 element of html into an h2 and returns the
// result with the number of headings it converted. It works on the
// x/net/html tokenizer's raw tokens: only the tag name of an h1 start, end
// or self-closing tag changes, and every other byte (attributes, text,
// comments, the content of script or style) is copied as it is. Text that
// merely looks like a tag inside raw-text elements or comments is not a
// tag and is not touched. html without an h1 comes back unchanged with 0.
func ConvertH1(html string) (string, int) {
	if !containsFold(html, "<h1") && !containsFold(html, "</h1") {
		return html, 0
	}
	z := xhtml.NewTokenizer(strings.NewReader(html))
	var b bytes.Buffer
	b.Grow(len(html))
	count := 0
	for {
		tt := z.Next()
		if tt == xhtml.ErrorToken {
			break
		}
		raw := z.Raw()
		switch tt {
		case xhtml.StartTagToken, xhtml.SelfClosingTagToken:
			if name, _ := z.TagName(); string(name) == "h1" && len(raw) >= 3 {
				b.WriteString("<h2")
				b.Write(raw[3:])
				count++
				continue
			}
		case xhtml.EndTagToken:
			if name, _ := z.TagName(); string(name) == "h1" && len(raw) >= 4 {
				b.WriteString("</h2")
				b.Write(raw[4:])
				continue
			}
		}
		b.Write(raw)
	}
	if count == 0 && b.String() == html {
		return html, 0
	}
	return b.String(), count
}

// CountH1 is the number of h1 start tags in html, as ConvertH1 counts them.
func CountH1(html string) int {
	_, n := ConvertH1(html)
	return n
}

func containsFold(s, sub string) bool {
	return strings.Contains(strings.ToLower(s), sub)
}