/**
 * Changes and resolves the slugs of dumps and playlists. A slug changes only
 * when someone edits it (the dump and playlist services call
 * {@link changeSlug} with the slug their edit form sent), and the slug it
 * leaves becomes an alias of the item, so that old links still reach it; the
 * routes that read an item by its page path resolve the slug with
 * {@link resolveSlug}, aliases included, and answer the item, whose current
 * slug the client then puts in its URL.
 *
 * @module
 */

import { APIException } from "../lib/api-exception.ts";
import { db, transaction } from "../db/connection.ts";
import {
  SLUG_TABLES,
  slugHolder,
  type SlugKind,
  uniqueSlug,
  validateSlug,
} from "../lib/slugify.ts";
import { slugify } from "../../shared/slug.ts";
import { RENAME_LIMITS } from "../../shared/validation.ts";

/**
 * Returns a free slug for a new item of `userId`'s titled `title`, for the
 * dump and playlist services to insert it with, inside their transaction.
 */
export function newSlug(kind: SlugKind, userId: string, title: string): string {
  return uniqueSlug(db, kind, userId, slugify(title));
}

/**
 * Returns the id of `userId`'s item of `kind` whose slug is or was `slug`, or
 * undefined when none is.
 */
export function resolveSlug(
  kind: SlugKind,
  userId: string,
  slug: string,
): string | undefined {
  return slugHolder(db, kind, userId, slug);
}

/**
 * Gives `item` the slug `slug`, keeping its current one as an alias. An alias
 * always names the item itself, so redirects never chain; taking back one of
 * the item's own aliases swaps it with the current slug. Unless `exempt` (a
 * moderator), an item's slug changes at most `RENAME_LIMITS.SLUG.count` times
 * in its window, counted from its aliases. A slug equal to the current one
 * changes nothing.
 *
 * @throws {APIException} 400 when `slug` isn't valid, 409 when another item
 * of the owner's holds it now or held it before, 429 when the item's slug
 * changed too often lately.
 */
export function changeSlug(
  kind: SlugKind,
  item: { id: string; userId: string; slug: string },
  slug: string,
  exempt: boolean,
): void {
  if (slug === item.slug) return;
  validateSlug(slug);
  const { items, aliases, itemId } = SLUG_TABLES[kind];
  const now = new Date();
  transaction(() => {
    const holder = slugHolder(db, kind, item.userId, slug);
    if (holder && holder !== item.id) {
      throw new APIException(409, `The slug "${slug}" is already taken`);
    }
    const { count, windowMs } = RENAME_LIMITS.SLUG;
    const recent = (db.prepare(
      `SELECT COUNT(*) AS n FROM ${aliases} WHERE ${itemId} = ? AND created_at > ?;`,
    ).get(item.id, new Date(now.getTime() - windowMs).toISOString()) as {
      n: number;
    }).n;
    if (!exempt && recent >= count) {
      throw new APIException(
        429,
        `A slug can only be changed ${count} times a day`,
      );
    }
    db.prepare(`DELETE FROM ${aliases} WHERE user_id = ? AND slug = ?;`)
      .run(item.userId, slug);
    db.prepare(
      `INSERT INTO ${aliases} (user_id, slug, ${itemId}, created_at) VALUES (?, ?, ?, ?);`,
    ).run(item.userId, item.slug, item.id, now.toISOString());
    db.prepare(`UPDATE ${items} SET slug = ? WHERE id = ?;`).run(slug, item.id);
  });
}