package sanitize

import "regexp"

var (
	imgTagRe     = regexp.MustCompile(`(?i)<img\b([^>]*)>`)
	imgSrcAttrRe = regexp.MustCompile(`(?i)\bsrc\s*=`)
	imgLazySrcRe = regexp.MustCompile(
		`(?i)\bdata-(?:src|original|lazy-src|url|image|href)\s*=\s*("([^"]*)"|'([^']*)')`,
	)
)

// promoteEmailImageSources copies lazy-load URLs into src when newsletters omit src.
func promoteEmailImageSources(html string) string {
	return imgTagRe.ReplaceAllStringFunc(html, func(tag string) string {
		attrs := imgTagRe.FindStringSubmatch(tag)
		if len(attrs) < 2 || imgSrcAttrRe.MatchString(attrs[1]) {
			return tag
		}
		lazy := imgLazySrcRe.FindStringSubmatch(attrs[1])
		if len(lazy) < 4 {
			return tag
		}
		var quote, url string
		if lazy[2] != "" {
			quote, url = `"`, lazy[2]
		} else {
			quote, url = `'`, lazy[3]
		}
		if url == "" {
			return tag
		}
		return "<img" + attrs[1] + ` src=` + quote + url + quote + ">"
	})
}

func SanitizeHTML(html string) string {
	if html == "" {
		return ""
	}
	html = StripHiddenEmailHTML(html)
	html = policy.Sanitize(html)
	html = promoteEmailImageSources(html)
	return stripUnsafeCSSURLs(html)
}