package httpd

import (
	"html/template"
	"path"
	"strings"

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

	"gitbay.org/gitbay/internal/gitutil"
)

// rewriteRelativeLinks makes relative hrefs and srcs in rendered repo
// content resolve on the forge: links go to blob pages, images to raw.
// go-org exports .org links as .html, so an .html target whose .org (or
// .md) source exists in the tree maps back to the source file.
func rewriteRelativeLinks(rendered template.HTML, p repoPage, baseDir string) template.HTML {
	ctx := &html.Node{Type: html.ElementNode, Data: "div", DataAtom: atom.Div}
	nodes, err := html.ParseFragment(strings.NewReader(string(rendered)), ctx)
	if err != nil {
		return rendered
	}
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode {
			for i, a := range n.Attr {
				isHref := a.Key == "href" && n.Data == "a"
				isSrc := a.Key == "src" && (n.Data == "img" || n.Data == "video" || n.Data == "source")
				if !isHref && !isSrc {
					continue
				}
				v := a.Val
				if v == "" || strings.Contains(v, "://") || strings.HasPrefix(v, "/") ||
					strings.HasPrefix(v, "#") || strings.HasPrefix(v, "mailto:") ||
					strings.HasPrefix(v, "data:") {
					continue
				}
				target := path.Clean(path.Join(baseDir, v))
				if strings.HasPrefix(target, "..") {
					continue
				}
				if isSrc {
					n.Attr[i].Val = "/" + p.Repo.Path() + "/raw/" + p.Ref + "/" + target
					continue
				}
				// .html from org/markdown exports maps back to the source.
				if strings.HasSuffix(target, ".html") {
					stem := strings.TrimSuffix(target, ".html")
					for _, ext := range []string{".org", ".md"} {
						if _, err := gitutil.ReadBlob(p.Dir, p.Ref, stem+ext, 1); err == nil {
							target = stem + ext
							break
						}
					}
				}
				n.Attr[i].Val = "/" + p.Repo.Path() + "/blob/" + p.Ref + "/" + target
			}
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	var out strings.Builder
	for _, n := range nodes {
		walk(n)
		if err := html.Render(&out, n); err != nil {
			return rendered
		}
	}
	return template.HTML(out.String())
}