import type { I18nConfig } from '../i18n/index.js'
import type { SystemPageRole } from './types.js'

import { buildLocalizedPath, getLocalizedSlugs } from '../i18n/index.js'

/**
 * The shape we need from an assigned system-page document: its localized slug
 * field, as returned by Payload when the parent is read with `locale: 'all'`.
 *
 * The plugin doesn't know the client's Pages type, so it depends only on this
 * minimal contract.
 */
type AssignedPage = {
  slug?: null | Record<string, unknown>
}

type GetSystemPagePathArgs = {
  config: I18nConfig
  /**
   * Slug that represents the site root. Defaults to 'home'. When the assigned
   * page's slug in the target locale equals this, the path collapses to the
   * locale root (/pl, /en).
   */
  homeSlug?: string
  /** Target locale to build the path for. */
  locale: string
  /**
   * The resolved system-page assignment from SiteSettings — the related
   * document object (not just an ID), read with `locale: 'all'` so its slug
   * is a locale→value map. Pass null/undefined if the role is unassigned.
   */
  page: AssignedPage | null | undefined
}

/**
 * Resolves a system-page assignment to a locale-aware path.
 *
 * Bridges the Pages module (which document plays a role) and the i18n module
 * (how that document's localized slug becomes a URL). This is what powers
 * "visit /pl → serve the homepage": read SiteSettings.homepage, pass the
 * related document here, get /pl/strona-glowna (or /pl if it's the home slug).
 *
 * Returns undefined when the role is unassigned or the assigned page has no
 * slug in the target locale — the caller decides the fallback (e.g. 404,
 * redirect to default locale).
 *
 * @example
 * const settings = await payload.findGlobal({ slug: 'site-settings', locale: 'all', depth: 1 })
 * getSystemPagePath({ page: settings.homepage, locale: 'pl', config })
 * // → '/pl'  (home slug collapses to root)
 * getSystemPagePath({ page: settings.privacyPolicy, locale: 'en', config })
 * // → '/en/privacy-policy'
 */
export function getSystemPagePath({
  config,
  homeSlug = 'home',
  locale,
  page,
}: GetSystemPagePathArgs): string | undefined {
  if (!page?.slug) {
    return undefined
  }

  const slugs = getLocalizedSlugs({ config, slugField: page.slug })
  return buildLocalizedPath({ config, homeSlug, locale, slugs })
}