feat: HTML sitemap groups API

- GET /_sitemap/api/v1/html?locale= answers the overview: the listed
  addresses of the XML sitemaps by group, in the order pages, offers,
  services, categories (as a tree), posts (newest first), tags, authors,
  other content types, each with its title in the locale, total, the
  first html_page_size links and more
- GET /_sitemap/api/v1/html/{group}?locale=&page= answers one page of a
  group; past the last page, an unknown group or the HTML sitemap off
  answer 404; every answer is noindex; per-IP bucket sitemap-html
- the HTML sitemap tab: html_enabled, the address per locale (html_paths)
  and html_page_size 50 to 500, with errors.html_path and errors.page_size
- contract.Listing.Settings answers HTMLEnabled, HTMLPaths, HTMLPageSize
  and KeyFile

controllers/api/html.go

@@ -0,0 +1,116 @@
+package api
+
+import (
+	"net/http"
+	"regexp"
+	"strconv"
+
+	"git.golem15.com/golem15/sm-sitemap-plugin/classes"
+	"git.golem15.com/golem15/summercms/modules/backpack"
+	"git.golem15.com/golem15/summercms/modules/wire"
+	"gorm.io/gorm"
+)
+
+// GroupPattern is the {group} constraint of the HTML sitemap group route:
+// a file group slug.
+const GroupPattern = `[a-z0-9][a-z0-9-]{0,63}`
+
+// localePattern is the form a locale query value must have.
+var localePattern = regexp.MustCompile(`^[a-z]{2,3}([-_][A-Za-z0-9]{2,8})*$`)
+
+// pagePattern is the form of the page query value: 1 to 6 digits.
+var pagePattern = regexp.MustCompile(`^[0-9]{1,6}$`)
+
+// htmlRequest checks the shared parts of an HTML sitemap request and
+// returns the settings and database, or answers 404 (the HTML sitemap is
+// off, a malformed locale) or 500 itself.
+func htmlRequest(app func() *backpack.App, w http.ResponseWriter, r *http.Request) (classes.HTMLSitemap, bool) {
+	w.Header().Set("X-Robots-Tag", "noindex")
+	w.Header().Set("Cache-Control", "no-cache, private")
+	a := app()
+	if a == nil {
+		http.NotFound(w, r)
+		return classes.HTMLSitemap{}, false
+	}
+	if loc := r.URL.Query().Get("locale"); loc != "" && !localePattern.MatchString(loc) {
+		http.NotFound(w, r)
+		return classes.HTMLSitemap{}, false
+	}
+	db, ok := a.Lookup[*gorm.DB]()
+	if !ok || db == nil {
+		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+		return classes.HTMLSitemap{}, false
+	}
+	return classes.HTMLSitemap{App: a, DB: db.WithContext(r.Context())}, true
+}
+
+// HTMLOverview serves GET /_sitemap/api/v1/html?locale=: the HTML sitemap
+// overview (D-34; classes.HTMLSitemap.Overview). It lists exactly the
+// addresses of the XML sitemaps and answers 404 while the HTML sitemap is
+// off. Every answer carries X-Robots-Tag: noindex.
+func HTMLOverview(app func() *backpack.App) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		h, ok := htmlRequest(app, w, r)
+		if !ok {
+			return
+		}
+		settings, err := classes.LoadSettings(h.DB)
+		if err != nil {
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		if !settings.HTMLEnabled {
+			http.NotFound(w, r)
+			return
+		}
+		out, err := h.Overview(r.Context(), settings, r.URL.Query().Get("locale"))
+		if err != nil {
+			log.Error("golem15.sitemap: html overview", "error", err)
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		wire.WriteJSON(w, http.StatusOK, out)
+	}
+}
+
+// HTMLGroup serves GET /_sitemap/api/v1/html/{group}?locale=&page=: one
+// page (from 1, the default) of a group (classes.HTMLSitemap.Group). An
+// unknown group, a page past the last, a malformed page or the HTML
+// sitemap off answer 404.
+func HTMLGroup(app func() *backpack.App) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		h, ok := htmlRequest(app, w, r)
+		if !ok {
+			return
+		}
+		page := 1
+		if raw := r.URL.Query().Get("page"); raw != "" {
+			n, err := strconv.Atoi(raw)
+			if !pagePattern.MatchString(raw) || err != nil || n < 1 {
+				http.NotFound(w, r)
+				return
+			}
+			page = n
+		}
+		settings, err := classes.LoadSettings(h.DB)
+		if err != nil {
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		if !settings.HTMLEnabled {
+			http.NotFound(w, r)
+			return
+		}
+		out, found, err := h.Group(r.Context(), settings, r.URL.Query().Get("locale"), r.PathValue("group"), page)
+		if err != nil {
+			log.Error("golem15.sitemap: html group", "error", err)
+			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
+			return
+		}
+		if !found {
+			http.NotFound(w, r)
+			return
+		}
+		wire.WriteJSON(w, http.StatusOK, out)
+	}
+}

controllers/api/logger.go

@@ -0,0 +1,7 @@
+package api
+
+import "git.golem15.com/golem15/summercms/modules/diary"
+
+// log is the handlers' logger: its records carry component=sitemap, like
+// the rest of the plugin (log.components.sitemap).
+var log = diary.For("sitemap")