feat(shared): add slug rules and shared document models

shared/provision/slug.go

@@ -0,0 +1,59 @@
+// Package provision holds the tenant creation rules shared by the control
+// plane and sitesvc.
+//
+// These rules used to be duplicated: the control plane owned one copy and
+// sitesvc mirrored it by hand. The copies had already drifted — sitesvc retried
+// on a lost slug race while the control plane returned an error. This package
+// is the single definition; neither service may reimplement any of it.
+package provision
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+const (
+	MinSlugLength = 3
+	MaxSlugLength = 40
+)
+
+var slugStrip = regexp.MustCompile(`[^a-z0-9]+`)
+
+// ReservedSlugs are subdomain labels the platform needs for itself.
+var ReservedSlugs = map[string]bool{
+	"www": true, "api": true, "app": true, "admin": true, "auth": true,
+	"install": true, "static": true, "_next": true, "default": true,
+}
+
+// Slugify lowercases a name and collapses every run of non-alphanumeric
+// characters into a single hyphen, trimming hyphens from both ends.
+func Slugify(name string) string {
+	s := strings.ToLower(name)
+	s = slugStrip.ReplaceAllString(s, "-")
+	return strings.Trim(s, "-")
+}
+
+// BaseSlug turns a name into a validated slug stem, or explains why it cannot.
+func BaseSlug(name string) (string, error) {
+	base := Slugify(name)
+	if len(base) < MinSlugLength {
+		return "", fmt.Errorf("organisation name too short (slug must be at least %d characters)", MinSlugLength)
+	}
+	if len(base) > MaxSlugLength {
+		base = base[:MaxSlugLength]
+	}
+	if ReservedSlugs[base] {
+		return "", fmt.Errorf("that organisation name is reserved")
+	}
+	return base, nil
+}
+
+// NextSlug returns the candidate slug for a given attempt. Attempt 1 is the
+// base itself; later attempts append a counter.
+func NextSlug(base string, attempt int) string {
+	if attempt < 2 {
+		return base
+	}
+	return fmt.Sprintf("%s-%d", base, attempt)
+}