// 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)
}