/**
 * TASK-0106 §3 — form slug generation.
 *
 * Kebab-case from the form name, ≤ 50 chars (LIMITS.MAX_SLUG), with a
 * deterministic `-2`/`-3`/… suffix on collision. The collision check +
 * insert is NOT atomic here — `FormsService` wraps the whole thing in a
 * transaction and the `forms.slug` unique index is the final arbiter
 * (P2002 → regenerate, max 3 attempts; spec §Security "race-safe").
 */
import { Prisma } from "@prisma/client";

/** A slug the client may provide (already kebab-shaped by its own UI). */
export const SLUG_INPUT_REGEX = /^[a-z0-9]+(?:-[a-z0-9]+)*$/;

const MAX_SLUG = 50;

/** Kebab-case a display name: lowercase, non-alphanumerics → `-`. */
export function kebabSlug(name: string): string {
  return name
    .toLowerCase()
    .normalize("NFKD")
    .replace(/[^a-z0-9]+/g, "-")
    .replace(/^-+|-+$/g, "");
}

/** A valid slug candidate: 2..50 chars, kebab. (Empty names → ""). */
export function normalizeSlug(name: string): string {
  return kebabSlug(name).slice(0, MAX_SLUG).replace(/-+$/g, "");
}

/**
 * `slug` with the next free collision suffix: `slug` itself when free,
 * else `slug-2`, `slug-3`, … (spec: "-2/-3 suffix on collision").
 *
 * `prisma` is the live client (or a transaction); `taken(slugs)` must
 * report which candidates are already used platform-wide (one query).
 */
export async function nextFreeSlug(
  base: string,
  taken: (slugs: string[]) => Promise<Set<string>>
): Promise<string> {
  const clean = base || "form";
  const first = await taken([clean]);
  if (!first.has(clean)) return clean;
  for (let n = 2; ; n++) {
    // Keep the total ≤ MAX_SLUG (suffix eats into the budget).
    const candidate = `${clean.slice(0, MAX_SLUG - String(n).length - 1)}-${n}`;
    const used = await taken([candidate]);
    if (!used.has(candidate)) return candidate;
    if (n > 1000) throw new Error(`slug generation exhausted for ${clean}`);
  }
}

/** True when a Prisma error is the `forms.slug` unique-constraint violation. */
export function isSlugConstraintError(err: unknown): boolean {
  return (
    err instanceof Prisma.PrismaClientKnownRequestError &&
    err.code === "P2002" &&
    (Array.isArray(err.meta?.target)
      ? (err.meta.target as string[]).includes("slug")
      : err.meta?.target === "slug")
  );
}