// Embed expansion for Journal HTML. The Blog Editor (Journal plugin,
// assets/src/blogeditor/embed.ts) never stores an iframe: it writes the
// placeholder <figure data-embed="youtube" data-id="ID"></figure>, and the
// plugin's bluemonday policy (classes/format_html.go) keeps exactly that, with
// data-embed matching ^youtube$ and data-id matching ^[A-Za-z0-9_-]{11}$.
// htmlGate.ts mirrors those two rules, so the placeholder survives the layer's
// sanitizer too.
//
// expandEmbeds is the very last step before v-html, after sanitizeJournalHtml:
// its input is always sanitizer output, and its output is never sanitized
// again (the sanitizer strips every iframe, including the one built here). The
// regex matches the serialization sanitize-html gives the placeholder:
// attribute order kept, double quotes, empty figure. Only a known provider
// with a valid id becomes an iframe, whose src is a fixed host plus that id;
// anything else is returned unchanged and stays an inert empty figure.

/** One allowlisted embed provider. */
export type EmbedProvider = {
  /** The id a placeholder must match to expand. */
  id: RegExp
  /** The iframe src for a validated id. */
  src: (id: string) => string
  /** The iframe's accessible title. */
  title: string
}

/** Providers a placeholder may name. YouTube only, on its privacy-enhanced host. */
export const EMBED_PROVIDERS: Readonly<Record<string, EmbedProvider>> = Object.freeze({
  youtube: {
    id: /^[A-Za-z0-9_-]{11}$/,
    src: (id: string) => `https://www.youtube-nocookie.com/embed/${id}`,
    title: 'YouTube video',
  },
})

/**
 * The placeholder exactly as the editor writes it and sanitize-html
 * serializes it. Group 1 is the provider, group 2 the id; neither may hold a
 * quote or an angle bracket.
 */
export const EMBED_PLACEHOLDER = /<figure data-embed="([^"<>]*)" data-id="([^"<>]*)"><\/figure>/g

/**
 * Replaces every placeholder whose provider is in EMBED_PROVIDERS and whose
 * id passes the provider's pattern with a figure holding the provider's
 * iframe. Every other match is returned unchanged. Empty input gives "".
 * Call it on sanitizeJournalHtml output only, and never sanitize its result.
 */
export function expandEmbeds(html: string | null | undefined): string {
  if (!html) return ''
  return html.replace(EMBED_PLACEHOLDER, (match: string, provider: string, id: string) => {
    if (!Object.hasOwn(EMBED_PROVIDERS, provider)) return match
    const p = EMBED_PROVIDERS[provider]!
    if (!p.id.test(id)) return match
    return (
      `<figure class="journal-embed journal-embed--${provider}">` +
      `<iframe src="${p.src(id)}" title="${p.title}" loading="lazy" ` +
      'referrerpolicy="strict-origin-when-cross-origin" ' +
      'allow="encrypted-media; picture-in-picture; fullscreen" allowfullscreen></iframe>' +
      '</figure>'
    )
  })
}