// SEO values for Journal pages. The page head comes from the CMS through
// vue-seo-layer (useCmsSeo); these values are the fallback a page applies
// only while there is no CMS answer for it (the SEO layer off with seo.cms
// false, the CMS unreachable, or a page the CMS does not know), so a site
// without the SEO plugin keeps its titles and no page gets two of them.
// The keys the CMS never sets (og:type, article:*) come from
// journalArticleMeta on every post page.

import type { JournalPost } from './types.ts'

/** Plain text of an HTML fragment: tags dropped, common entities decoded, whitespace collapsed. */
export function htmlToText(html: string | null | undefined): string {
  if (!html) return ''
  return html
    .replace(/<(script|style)\b[\s\S]*?<\/\1>/gi, ' ')
    .replace(/<[^>]*>/g, ' ')
    .replace(/&nbsp;/g, ' ')
    .replace(/&quot;/g, '"')
    .replace(/&#39;|&apos;/g, "'")
    .replace(/&lt;/g, '<')
    .replace(/&gt;/g, '>')
    .replace(/&amp;/g, '&')
    .replace(/\s+/g, ' ')
    .trim()
}

/** Cuts `text` to at most `max` characters, at a word boundary when one is near, with an ellipsis. */
export function truncateText(text: string, max: number = 160): string {
  if (text.length <= max) return text
  const cut = text.slice(0, max - 1)
  const space = cut.lastIndexOf(' ')
  return `${(space > max * 0.6 ? cut.slice(0, space) : cut).trimEnd()}…`
}

/** Makes `url` absolute against `siteUrl`; already absolute URLs and a missing siteUrl pass through. */
export function absoluteUrl(url: string, siteUrl?: string | null): string {
  if (/^https?:\/\//i.test(url) || !siteUrl) return url
  return `${siteUrl.replace(/\/+$/, '')}/${url.replace(/^\/+/, '')}`
}

export interface JournalPostSeo {
  title: string
  ogTitle: string
  description: string
  ogDescription: string
  ogType: 'article'
  ogImage?: string
  articlePublishedTime?: string
  articleModifiedTime?: string
}

/**
 * Meta for a post page: the post title, the excerpt (or the first 160
 * characters of the body text) as description, the featured image as
 * og:image, and the publish and update times.
 */
export function postSeoMeta(post: JournalPost, siteUrl?: string | null): JournalPostSeo {
  const description = truncateText(htmlToText(post.excerpt) || htmlToText(post.content_html), 160)
  const meta: JournalPostSeo = {
    title: post.title,
    ogTitle: post.title,
    description,
    ogDescription: description,
    ogType: 'article',
  }
  if (post.featured_image_url) meta.ogImage = absoluteUrl(post.featured_image_url, siteUrl)
  if (post.published_at) meta.articlePublishedTime = post.published_at
  if (post.updated_at) meta.articleModifiedTime = post.updated_at
  return meta
}

/**
 * The post-page head keys the CMS head never carries (vue-seo-layer writes
 * no og:type and no article:* tags): og:type article and the publish and
 * update times, set on every post page whether or not the CMS answers
 * (L4 WR-02). A missing time is left out.
 */
export function journalArticleMeta(post: Pick<JournalPost, 'published_at' | 'updated_at'>): Pick<JournalPostSeo, 'ogType' | 'articlePublishedTime' | 'articleModifiedTime'> {
  const meta: Pick<JournalPostSeo, 'ogType' | 'articlePublishedTime' | 'articleModifiedTime'> = { ogType: 'article' }
  if (post.published_at) meta.articlePublishedTime = post.published_at
  if (post.updated_at) meta.articleModifiedTime = post.updated_at
  return meta
}

/** True when the resolve answer sets the page head (an ok answer with head values). */
export function cmsHeadPresent(answer: { action?: string; seo?: unknown } | null | undefined): boolean {
  return answer?.action === 'ok' && !!answer.seo && typeof answer.seo === 'object'
}

/**
 * The origin to make page URLs absolute on: the CMS's page URL (the site
 * URL the backend knows) when there is an answer, else `fallback` (the
 * request's origin).
 */
export function journalSiteOrigin(answerUrl: string | null | undefined, fallback: string): string {
  if (typeof answerUrl === 'string' && /^https?:\/\//i.test(answerUrl)) {
    try {
      return new URL(answerUrl).origin
    } catch {
      // fall through
    }
  }
  return fallback
}

/**
 * The post title's element (UI-SPEC L6): the option journal.postTitleTag
 * when it is 'h1' or 'p', otherwise ('auto') h1 while the Journal H1 setting
 * is on (content_h1_to_h2 true or absent) and p while it is off, so the
 * page keeps exactly one H1 either way.
 */
export function journalPostTitleTag(option: unknown, contentH1ToH2: boolean | null | undefined): 'h1' | 'p' {
  if (option === 'h1' || option === 'p') return option
  return contentH1ToH2 === false ? 'p' : 'h1'
}

/** A schema.org ItemList node of a listing page (D-43). */
export interface JournalItemListNode {
  '@type': 'ItemList'
  '@id': string
  itemListElement: Array<{ '@type': 'ListItem'; position: number; url: string }>
  [key: string]: unknown
}

/**
 * The ItemList node of a listing page for its one JSON-LD graph (D-43):
 * @id <pageUrl>#itemlist and a ListItem with the absolute URL of each post
 * shown, positions continuing across pages from `first` (1 on page 1). Posts
 * without a link (a disabled post view) are left out; none gives null.
 */
export function journalItemList(pageUrl: string, origin: string, paths: ReadonlyArray<string | null | undefined>, first: number = 1): JournalItemListNode | null {
  const items: JournalItemListNode['itemListElement'] = []
  for (const path of paths) {
    if (typeof path === 'string' && path !== '') items.push({ '@type': 'ListItem', position: first + items.length, url: absoluteUrl(path, origin) })
  }
  if (items.length === 0) return null
  return { '@type': 'ItemList', '@id': `${pageUrl.split('#')[0]}#itemlist`, itemListElement: items }
}

/** A listing title; pages after the first append the "Page N" string. */
export function listTitle(base: string, page: number, pageTitle: string): string {
  return page > 1 ? `${base} · ${pageTitle}` : base
}