/* Route-shape helpers for the reader experience.

   An article route is a page of the open book drawn by ArticleBookStack —
   pages laid out side by side, older ones parked with their spines showing —
   while the article edit page and the new-article page remain plain,
   full-height pages. An article lives at /wiki/<slug>; one of its language
   versions at /wiki/<lang>/<slug>, e.g. /wiki/fr/bayes-theorem. */

const READER_PATH = /^\/wiki\/([^/]+?)\/?$/
const VERSION_READER_PATH = /^\/wiki\/([a-z]{2})\/([^/]+?)\/?$/
const WIKI_SUB_PATH = /^\/wiki\/[^/]+\/[^/]+/

/** What a reader address names: the article's identity, and which language
 *  version the address asks for (null for the article's own version). */
export interface ReaderLocation {
  identity: string
  lang: string | null
}

export function parseReaderPath(path: string): ReaderLocation | null {
  const version = VERSION_READER_PATH.exec(path)
  // /wiki/<x>/edit is the editor whatever <x> is — never a version address
  if (version && version[2]!.toLowerCase() !== 'edit') {
    return { identity: decodeURIComponent(version[2]!), lang: version[1]! }
  }
  const plain = READER_PATH.exec(path)
  if (plain) return { identity: decodeURIComponent(plain[1]!), lang: null }
  return null
}

export function isReaderPath(path: string): boolean {
  return parseReaderPath(path) !== null
}

export function wikiSlugFromPath(path: string): string | null {
  return parseReaderPath(path)?.identity ?? null
}

/**
 * The address of one language version: the canonical document lives at the
 * article's own URL, translations at /wiki/<lang>/<identity>.
 */
export function versionHref(identity: string, version: { language?: string; slug: string }): string {
  if (version.slug === identity) return `/wiki/${encodeURIComponent(identity)}`
  return `/wiki/${encodeURIComponent(version.language ?? 'en')}/${encodeURIComponent(identity)}`
}

/**
 * The "reading surface": the reader itself plus the edit/new-article pages —
 * the pages that belong to the open book. The stack of open pages survives the
 * whole session either way; this marks the pages outside it (the list, the
 * graph, home), which are the places worth returning to once the last page is
 * closed.
 */
export function isReadingSurface(path: string): boolean {
  return isReaderPath(path) || WIKI_SUB_PATH.test(path) || path === '/new'
}