/**
 * Picks and checks the slugs of dumps and playlists, which name them in their
 * page URLs under their owner: `/@bob/dumps/<slug>`, `/@bob/playlists/<slug>`.
 * Each kind has its own slug space per owner, shared by the items' current
 * slugs and their aliases (the slugs they had before). `services/slug-service.ts`
 * changes and resolves slugs with these, and migration 0021 gave every item
 * one; both pass the database, since this module doesn't open it.
 *
 * @module
 */

import type { DatabaseSync } from "node:sqlite";
import { APIException } from "./api-exception.ts";
import { isValidSlug, SLUG_MAX } from "../../shared/slug.ts";

/** A kind of item that has a slug under its owner. */
export type SlugKind = "dump" | "playlist";

/** Where each {@link SlugKind}'s slugs live. */
export const SLUG_TABLES: Record<
  SlugKind,
  { items: string; aliases: string; itemId: string }
> = {
  dump: { items: "dumps", aliases: "dump_slug_aliases", itemId: "dump_id" },
  playlist: {
    items: "playlists",
    aliases: "playlist_slug_aliases",
    itemId: "playlist_id",
  },
};

/**
 * Returns the id of the item whose current slug or alias is `slug` in
 * `userId`'s space for `kind`, or undefined when it is free.
 */
export function slugHolder(
  db: DatabaseSync,
  kind: SlugKind,
  userId: string,
  slug: string,
): string | undefined {
  const { items, aliases, itemId } = SLUG_TABLES[kind];
  const row = db.prepare(
    `SELECT id FROM ${items} WHERE user_id = ? AND slug = ?
     UNION ALL
     SELECT ${itemId} FROM ${aliases} WHERE user_id = ? AND slug = ?
     LIMIT 1;`,
  ).get(userId, slug, userId, slug) as { id: string } | undefined;
  return row?.id;
}

/**
 * Returns `base`, or `base-2`, `base-3`… cut to fit, whichever is free in
 * `userId`'s space for `kind`. `base` must be a valid slug, as `slugify`
 * makes. The services take it on creating an item, the migration on
 * re-slugging one, inside the transaction that writes it.
 */
export function uniqueSlug(
  db: DatabaseSync,
  kind: SlugKind,
  userId: string,
  base: string,
): string {
  for (let n = 1;; n++) {
    const suffix = n === 1 ? "" : `-${n}`;
    const candidate = `${
      base.substring(0, SLUG_MAX - suffix.length).replace(/-+$/, "")
    }${suffix}`;
    if (!slugHolder(db, kind, userId, candidate)) return candidate;
  }
}

/**
 * Throws a 400 unless `slug` is a valid slug, lowercase words of letters and
 * digits joined by hyphens, at most `max` long. slug-service checks a dump's
 * or a playlist's with it, and category-service a category's, with that
 * kind's own limit.
 */
export function validateSlug(slug: string, max: number = SLUG_MAX): void {
  if (!isValidSlug(slug, max)) {
    throw new APIException(
      400,
      `Slug must be lowercase letters, numbers and hyphens, at most ${max} characters`,
    );
  }
}