package classes

import (
	"regexp"
	"strings"

	"git.golem15.com/golem15/sm-sitemap-plugin/models"
)

// The PHP routes.php patterns of the frontend rewrite.
var (
	locElement   = regexp.MustCompile(`<loc>(.*?)</loc>`)
	xhtmlLinkRef = regexp.MustCompile(`(<xhtml:link[^>]*href=")([^"]*)(")`)
)

// Rewrite is the frontend_url rewrite of PHP routes.php: with frontendURL
// set, backendURL is replaced literally (str_replace) inside every loc
// element, inside every xhtml:link href and in the exact stylesheet href.
// Both URLs are right-trimmed of slashes first. An empty frontendURL (or
// "0", which PHP reads as false) leaves xml unchanged.
//
// PHP inserted the stored text as it was. Three rules keep that text out of
// the document unless it is a plain http(s) URL (T-17-15):
//
//   - a frontendURL that models.AllowedFrontendURL refuses leaves xml
//     unchanged, whatever is stored in the settings row;
//   - the frontend URL is inserted through EscapeText in loc and through
//     EscapeAttr in the hrefs. Both are the identity for every accepted
//     value, which keeps the PHP bytes;
//   - a loc or xhtml:link href whose rewritten value does not start with
//     http:// or https:// keeps its value. The generator applies the same
//     filter before the rewrite.
func Rewrite(xml, backendURL, frontendURL string) string {
	if frontendURL == "" || frontendURL == "0" {
		return xml
	}
	if !models.AllowedFrontendURL(frontendURL) {
		return xml
	}
	frontend := strings.TrimRight(frontendURL, "/")
	backend := strings.TrimRight(backendURL, "/")
	if backend == "" {
		return xml
	}
	frontendText, frontendAttr := EscapeText(frontend), EscapeAttr(frontend)
	xml = locElement.ReplaceAllStringFunc(xml, func(m string) string {
		inner := m[len("<loc>") : len(m)-len("</loc>")]
		rewritten := strings.ReplaceAll(inner, backend, frontendText)
		if !httpURL(rewritten) {
			return m
		}
		return "<loc>" + rewritten + "</loc>"
	})
	xml = xhtmlLinkRef.ReplaceAllStringFunc(xml, func(m string) string {
		sub := xhtmlLinkRef.FindStringSubmatch(m)
		rewritten := strings.ReplaceAll(sub[2], backend, frontendAttr)
		if !httpURL(rewritten) {
			return m
		}
		return sub[1] + rewritten + sub[3]
	})
	return strings.ReplaceAll(xml, `href="`+backend+`/sitemap.xsl"`, `href="`+frontendAttr+`/sitemap.xsl"`)
}

// BackendURL is PHP rtrim(url('/'), '/') for a request whose root URL is
// root: the URL the rewrite replaces.
func BackendURL(root string) string {
	return strings.TrimRight(URLTo(root, "/"), "/")
}