// The layer's label dictionary (UI-SPEC L8): the strings of the public
// layer components in en and pl, without an i18n dependency. useSeoLabels()
// picks the page's content locale; an app overrides or adds locales in
// app.config.ts under seo.labels.<locale>, and component props override
// both. Breadcrumb names and sitemap group headings come from the CMS and
// are never translated here. Pure, so `node --test` drives it directly.

export interface SeoLabels {
  breadcrumbs: { label: string }
  pagination: { label: string; previous: string; next: string; page: string }
  sitemap: { title: string; groupTitle: string; pageSuffix: string; all: string; empty: string }
  sitemapLink: string
  links: { newTab: string }
}

export type SeoLabelOverrides = Record<string, DeepPartial<SeoLabels>>

type DeepPartial<T> = { [K in keyof T]?: T[K] extends object ? DeepPartial<T[K]> : T[K] }

/** The built-in dictionaries. {name} marks a placeholder (formatSeoLabel). */
export const SEO_LABELS: Readonly<Record<'en' | 'pl', SeoLabels>> = Object.freeze({
  en: {
    breadcrumbs: { label: 'Breadcrumbs' },
    pagination: { label: 'Pagination', previous: 'Previous page', next: 'Next page', page: 'Page {page}' },
    sitemap: {
      title: 'Sitemap',
      groupTitle: 'Sitemap: {group}',
      pageSuffix: 'Page {page}',
      all: '{group}: all ({count})',
      empty: 'There are no pages to list yet.',
    },
    sitemapLink: 'Sitemap',
    links: { newTab: '(opens in a new tab)' },
  },
  pl: {
    breadcrumbs: { label: 'Ścieżka nawigacji' },
    pagination: { label: 'Stronicowanie', previous: 'Poprzednia strona', next: 'Następna strona', page: 'Strona {page}' },
    sitemap: {
      title: 'Mapa strony',
      groupTitle: 'Mapa strony: {group}',
      pageSuffix: 'Strona {page}',
      all: '{group}: wszystkie ({count})',
      empty: 'Nie ma jeszcze stron do wyświetlenia.',
    },
    sitemapLink: 'Mapa strony',
    links: { newTab: '(otwiera się w nowej karcie)' },
  },
})

/** A copy of `base` with every string of `over` at a key `base` has. */
function merge<T>(base: T, over: unknown): T {
  if (!over || typeof over !== 'object' || Array.isArray(over)) return base
  const out = { ...(base as Record<string, unknown>) }
  for (const [key, value] of Object.entries(over as Record<string, unknown>)) {
    if (!(key in out)) continue
    const current = out[key]
    if (typeof current === 'string') {
      if (typeof value === 'string') out[key] = value
    } else if (current && typeof current === 'object') {
      out[key] = merge(current, value)
    }
  }
  return out as T
}

const primary = (code: string) => code.toLowerCase().split(/[-_]/)[0] ?? ''

/**
 * The dictionary for a page: the first of the resolve answer's locale, its
 * primary subtag and html_lang's primary subtag that the layer or the app
 * overrides know, else en. Missing keys come from en; an app override for
 * the chosen locale wins key by key.
 */
export function pickLabels(locale: string | undefined | null, htmlLang: string | undefined | null, overrides: SeoLabelOverrides = {}): SeoLabels {
  const known = (code: string) => code !== '' && (code in SEO_LABELS || (overrides && Object.prototype.hasOwnProperty.call(overrides, code)))
  const l = (locale ?? '').toLowerCase()
  const candidates = [l, primary(l), primary(htmlLang ?? '')]
  const code = candidates.find(known) ?? 'en'
  const builtIn = (SEO_LABELS as Record<string, SeoLabels>)[code]
  const base = code === 'en' ? SEO_LABELS.en : merge(SEO_LABELS.en, builtIn)
  return merge(base, overrides?.[code])
}

/** `template` with each {name} replaced by values[name]; unknown placeholders stay. */
export function formatSeoLabel(template: string, values: Record<string, string | number>): string {
  return template.replace(/\{(\w+)\}/g, (m, name: string) => (name in values ? String(values[name]) : m))
}