feat: JSON-LD graph, breadcrumbs and hreflang in the resolve answer (tracer)

- classes/schema builds one @graph per page (WebPage, article, profile,
  service, BreadcrumbList, VideoObject, WebSite, publisher) linked by @id
- breadcrumb trail through the primary parent chain, hreflang alternates
  with x-default, html_lang and og:locale in the resolve answer
- migration 202610280004 adds the publisher, local business, home crumb
  and pagination settings columns

classes/alternates.go

@@ -0,0 +1,119 @@
+package classes
+
+import (
+	"strings"
+
+	"git.golem15.com/golem15/summercms/modules/pact"
+)
+
+// OGLocalesConfigKey maps locale codes to og:locale values (D-55); unset
+// codes fall back to DefaultOGLocales, else <code>_<CODE>.
+const OGLocalesConfigKey = "golem15.seo.og_locales"
+
+// SearchURLConfigKey is the site search address with the
+// {search_term_string} placeholder (P33-25); empty means no SearchAction.
+const SearchURLConfigKey = "golem15.seo.search_url"
+
+// DefaultOGLocales are the og:locale values of the common locales.
+var DefaultOGLocales = map[string]string{"pl": "pl_PL", "en": "en_US", "de": "de_DE"}
+
+// Alternate is one hreflang alternate of a page (D-55): a language tag or
+// x-default and the absolute URL.
+type Alternate struct {
+	Hreflang string `json:"hreflang"`
+	URL      string `json:"url"`
+}
+
+// LangTag turns a locale code into its language tag: pl stays pl, pt_BR
+// and pt-br become pt-BR (the region is kept when the locale has one).
+func LangTag(locale string) string {
+	locale = strings.TrimSpace(strings.ReplaceAll(locale, "_", "-"))
+	lang, region, ok := strings.Cut(locale, "-")
+	if !ok || region == "" {
+		return strings.ToLower(lang)
+	}
+	return strings.ToLower(lang) + "-" + strings.ToUpper(region)
+}
+
+// OGLocale is the og:locale value of locale: the configured value, else
+// the default table, else the language with its region (pt_BR) or the
+// language doubled (fr_FR).
+func (s *Service) OGLocale(locale string) string {
+	tag := LangTag(locale)
+	if tag == "" {
+		return ""
+	}
+	if cfg := s.Config(); cfg != nil {
+		for _, key := range []string{locale, tag, strings.ToLower(tag)} {
+			if v := strings.TrimSpace(cfg.String(OGLocalesConfigKey + "." + key)); v != "" {
+				return v
+			}
+		}
+	}
+	if v, ok := DefaultOGLocales[tag]; ok {
+		return v
+	}
+	lang, region, ok := strings.Cut(tag, "-")
+	if ok {
+		return lang + "_" + region
+	}
+	return lang + "_" + strings.ToUpper(lang)
+}
+
+// translatedLocales lists the locales of rec with a public address, in the
+// record's order.
+func translatedLocales(rec *pact.ContentRecord) []pact.ContentLocale {
+	if rec == nil {
+		return nil
+	}
+	var out []pact.ContentLocale
+	seen := map[string]bool{}
+	for _, l := range rec.Locales {
+		if strings.TrimSpace(l.URL) == "" || l.Locale == "" || seen[l.Locale] {
+			continue
+		}
+		seen[l.Locale] = true
+		out = append(out, l)
+	}
+	return out
+}
+
+// Alternates lists the hreflang alternates of a record (D-55 to D-57):
+// each translated locale with its absolute URL, the page itself included,
+// then x-default on the default locale's URL. A record translated into one
+// locale only has none; a locale without a translation is absent.
+func Alternates(site string, rec *pact.ContentRecord, defaultLocale string) []Alternate {
+	locales := translatedLocales(rec)
+	if len(locales) < 2 {
+		return []Alternate{}
+	}
+	out := make([]Alternate, 0, len(locales)+1)
+	xDefault := ""
+	for _, l := range locales {
+		u := AbsoluteURL(site, l.URL)
+		out = append(out, Alternate{Hreflang: LangTag(l.Locale), URL: u})
+		if l.Locale == defaultLocale {
+			xDefault = u
+		}
+	}
+	if xDefault != "" {
+		out = append(out, Alternate{Hreflang: "x-default", URL: xDefault})
+	}
+	return out
+}
+
+// OGLocaleAlternates are the og:locale:alternate values of a record: one
+// per other translated locale.
+func (s *Service) OGLocaleAlternates(rec *pact.ContentRecord, locale string) []string {
+	out := []string{}
+	locales := translatedLocales(rec)
+	if len(locales) < 2 {
+		return out
+	}
+	for _, l := range locales {
+		if l.Locale != locale {
+			out = append(out, s.OGLocale(l.Locale))
+		}
+	}
+	return out
+}