// Shared slug policy used by namespace and repository slugs. Browser-safe so
// the same validator runs in SSR pages and Worker validation paths.
//
// The regex enforces lowercase ASCII alphanumerics with internal dashes.
// Length is bounded at 1..40. Reserved slugs cover Worker-owned routes and
// common static paths so that creating a namespace cannot shadow existing
// surfaces.

const SLUG_PATTERN = /^[a-z0-9](?:[a-z0-9-]{0,38}[a-z0-9])?$/;
export const SLUG_MAX_LENGTH = 40;

export const RESERVED_SLUGS: readonly string[] = [
  "auth",
  "sign-in",
  "sign-out",
  "api",
  "assets",
  "_cache",
  "_routes",
  "favicon.ico",
  "robots.txt",
];

const reservedSet: ReadonlySet<string> = new Set(RESERVED_SLUGS);

export function isValidSlug(input: string): boolean {
  if (typeof input !== "string") return false;
  if (input.length === 0 || input.length > SLUG_MAX_LENGTH) return false;
  if (!SLUG_PATTERN.test(input)) return false;
  if (reservedSet.has(input)) return false;
  return true;
}

export type SlugValidation =
  | { ok: true; slug: string }
  | { ok: false; reason: "format" | "reserved" | "length" };

// Granular result so the route handler can decide which message to surface
// (taken vs format vs reserved) without re-checking the regex.
export function validateSlugForRoute(input: string): SlugValidation {
  if (typeof input !== "string" || input.length === 0) {
    return { ok: false, reason: "length" };
  }
  if (input.length > SLUG_MAX_LENGTH) return { ok: false, reason: "length" };
  if (reservedSet.has(input)) return { ok: false, reason: "reserved" };
  if (!SLUG_PATTERN.test(input)) return { ok: false, reason: "format" };
  return { ok: true, slug: input };
}