feat: migrate definitions into additional addresses

- migration 202610280002 copies the served definition's url items into
  extra_urls, frontend_url into site_url and frontend_default_locale into
  default_locale; reference items are dropped
- the definitions table and the Phase 17 columns keep their data, so a
  rollback loses nothing (TestMigrateDefinitions)

updates/202610280002_update_golem15_sitemap_settings.go

@@ -1,6 +1,10 @@
 package updates
 
 import (
+	"encoding/json"
+	"strings"
+
+	"git.golem15.com/golem15/sm-sitemap-plugin/models"
 	"github.com/go-gormigrate/gormigrate/v2"
 	"gorm.io/gorm"
 )
@@ -33,7 +37,10 @@ var updateSettings = []*gormigrate.Migration{
 					return err
 				}
 			}
-			return tx.Exec(`INSERT INTO golem15_sitemap_settings (id) VALUES (1) ON CONFLICT (id) DO NOTHING`).Error
+			if err := tx.Exec(`INSERT INTO golem15_sitemap_settings (id) VALUES (1) ON CONFLICT (id) DO NOTHING`).Error; err != nil {
+				return err
+			}
+			return copyDefinitions(tx)
 		},
 		Rollback: func(tx *gorm.DB) error {
 			for _, name := range []string{"site_url", "file_size", "default_locale", "extra_urls", "rebuild_pending_until", "numbered_size", "built_at", "rebuild_requested_at"} {
@@ -49,3 +56,56 @@ var updateSettings = []*gormigrate.Migration{
 func init() {
 	Register(updateSettings...)
 }
+
+// copyDefinitions moves the Phase 17 data into the new columns (D-32): the
+// url items of the definition /sitemap.xml served (theme default, the
+// first one) become the additional addresses as given, without a lastmod
+// (an address that models.AllowedAddress refuses, or one already copied,
+// is skipped); frontend_url becomes site_url when models.AllowedFrontendURL
+// accepts it, and frontend_default_locale default_locale. Reference items
+// are dropped: the content types list their records. The definitions table
+// and the Phase 17 columns are left as they are, so a rollback (which drops
+// the new columns) keeps every value.
+func copyDefinitions(tx *gorm.DB) error {
+	var data []string
+	if err := tx.Raw(`SELECT COALESCE(data, '') FROM golem15_sitemap_definitions WHERE theme = 'default' ORDER BY id ASC LIMIT 1`).Scan(&data).Error; err != nil {
+		return err
+	}
+	rows := []models.ExtraURL{}
+	if len(data) > 0 {
+		items, _, err := models.ParseLegacyItems([]byte(data[0]))
+		if err != nil {
+			// A definition the Phase 17 code could not read either: nothing
+			// is copied, and the row stays for a manual look.
+			items = nil
+		}
+		seen := map[string]bool{}
+		for _, item := range items {
+			u := strings.TrimSpace(item.URL)
+			if item.Type != models.LegacyItemURL || seen[u] || !models.AllowedAddress(u) {
+				continue
+			}
+			seen[u] = true
+			rows = append(rows, models.ExtraURL{URL: u})
+		}
+	}
+	raw, err := json.Marshal(rows)
+	if err != nil {
+		return err
+	}
+	var old struct {
+		FrontendURL *string `gorm:"column:frontend_url"`
+		Locale      *string `gorm:"column:frontend_default_locale"`
+	}
+	if err := tx.Raw(`SELECT frontend_url, frontend_default_locale FROM golem15_sitemap_settings WHERE id = 1`).Scan(&old).Error; err != nil {
+		return err
+	}
+	var site, locale any
+	if u := strings.TrimSpace(models.Text(old.FrontendURL)); u != "" && models.AllowedFrontendURL(u) {
+		site = u
+	}
+	if l := strings.TrimSpace(models.Text(old.Locale)); l != "" {
+		locale = l
+	}
+	return tx.Exec(`UPDATE golem15_sitemap_settings SET extra_urls = ?::jsonb, site_url = ?, default_locale = ? WHERE id = 1`, string(raw), site, locale).Error
+}