package web

import (
	"fmt"
	"io/fs"
	"log/slog"
	"net/http"
	"strings"

	"khosra/internal/content"
)

// robots and sitemap are the two files a crawler looks for by exact name.
const (
	robotsPath  = "/robots.txt"
	sitemapPath = "/sitemap.xml"
)

// serveRobots answers /robots.txt, preferring the site's own file.
//
// A site that ships robots.txt has said something deliberate, so it is served verbatim; otherwise the engine
// emits the minimum that is true — everything is public, and here is the sitemap. The Sitemap line only
// appears with a declared base, because a relative sitemap reference is not something a crawler accepts.
func serveRobots(w http.ResponseWriter, req *http.Request, siteFS fs.FS, base string) {
	if siteFS != nil {
		if data, err := fs.ReadFile(siteFS, "robots.txt"); err == nil {
			writeAs(w, "text/plain; charset=utf-8", data, "robots.txt")
			return
		}
	}
	var out strings.Builder
	out.WriteString("User-agent: *\nDisallow:\n")
	if base != "" {
		fmt.Fprintf(&out, "Sitemap: %s\n", content.Absolute(base, sitemapPath))
	}
	writeAs(w, "text/plain; charset=utf-8", []byte(out.String()), "robots.txt")
}

// serveSitemap answers /sitemap.xml with every bundle in every language it exists in.
//
// It needs a declared base: the sitemap format has no room for a relative URL, so without one the honest
// answer is that this file does not exist rather than a file full of paths no crawler can use (ADR-0039).
// Every URL comes from content.URL, like every other path the engine emits, so a sitemap can never disagree
// with what is actually served.
func serveSitemap(w http.ResponseWriter, req *http.Request, site *content.Site, base string) {
	if base == "" {
		slog.Warn("no sitemap: the site declares no base URL", "file", content.SettingsFile)
		http.NotFound(w, req)
		return
	}
	var out strings.Builder
	out.WriteString(`<?xml version="1.0" encoding="utf-8"?>` + "\n")
	out.WriteString(`<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">` + "\n")
	for _, entry := range site.Everything() {
		fmt.Fprintf(&out, "<url><loc>%s</loc>", xmlEscape(content.Absolute(base, content.URL(entry.Route, entry.Lang))))
		if !entry.Date.IsZero() {
			fmt.Fprintf(&out, "<lastmod>%s</lastmod>", entry.Date.Format("2006-01-02"))
		}
		out.WriteString("</url>\n")
	}
	out.WriteString("</urlset>\n")
	writeAs(w, "application/xml; charset=utf-8", []byte(out.String()), "sitemap.xml")
}

// xmlEscape escapes the five characters XML reserves. A URL should contain none of them, and a sitemap that
// silently breaks on the one that does is worse than a slightly paranoid replacement.
func xmlEscape(s string) string {
	return strings.NewReplacer(
		"&", "&amp;", "<", "&lt;", ">", "&gt;", `"`, "&quot;", "'", "&apos;",
	).Replace(s)
}