/**
 * Walkt einen vom CMS gelieferten Page-/Post-Content-Tree und sanitisiert
 * Felder, die später roh über `{@html}` gerendert werden — primär das
 * `html`-Feld von HtmlBlocks.
 *
 * Wird in den Server-Loads aufgerufen (`+layout.server.ts`, `+page.server.ts`),
 * **nachdem** `resolveContentImages` etc. den Tree fertig aufgelöst haben.
 * Die Daten landen anschließend als sanitiertes HTML in der Page-Data, sodass
 * Svelte-Komponenten beim Render (Server + Client) keine zusätzliche Filter-
 * Logik brauchen.
 *
 * Server-only (`sanitize-html` braucht Node-APIs). Komponenten dürfen das
 * Modul daher nicht importieren — der `.server.ts`-Suffix erzwingt das.
 */
import sanitizeHtml from 'sanitize-html';

const HTML_BLOCK_OPTIONS: sanitizeHtml.IOptions = {
  // Allowlist: bewusst restriktiv. Alles, was nicht in `allowedTags` steht,
  // wird entfernt. `allowedSchemes` blockiert javascript:, data: usw.
  allowedTags: [
    'p', 'br', 'hr',
    'h1', 'h2', 'h3', 'h4', 'h5', 'h6',
    'strong', 'em', 'b', 'i', 'u', 's', 'sub', 'sup', 'mark',
    'a', 'blockquote', 'cite', 'q',
    'ul', 'ol', 'li',
    'pre', 'code', 'kbd', 'samp',
    'table', 'thead', 'tbody', 'tfoot', 'tr', 'th', 'td',
    'div', 'span', 'section', 'article', 'aside', 'figure', 'figcaption',
    'img', 'picture', 'source',
    'iframe',
  ],
  allowedAttributes: {
    a: ['href', 'name', 'target', 'rel', 'title'],
    img: ['src', 'srcset', 'sizes', 'alt', 'width', 'height', 'loading', 'decoding'],
    source: ['src', 'srcset', 'sizes', 'type', 'media'],
    iframe: [
      'src', 'width', 'height', 'allow', 'allowfullscreen',
      'referrerpolicy', 'loading', 'title', 'frameborder',
    ],
    '*': ['class', 'id', 'style', 'data-*', 'aria-*'],
  },
  allowedSchemes: ['http', 'https', 'mailto', 'tel'],
  allowedSchemesByTag: {
    img: ['http', 'https', 'data'],
  },
  allowedIframeHostnames: [
    'www.youtube.com',
    'youtube.com',
    'www.youtube-nocookie.com',
    'player.vimeo.com',
    'open.spotify.com',
  ],
  allowProtocolRelative: false,
  transformTags: {
    a: (tagName, attribs) => ({
      tagName,
      attribs: {
        ...attribs,
        rel: attribs.target === '_blank' ? 'noopener noreferrer' : (attribs.rel ?? ''),
      },
    }),
  },
};

/**
 * Pro-Block-Hash-Cache: sanitize-html ist teuer (~ms pro KB), das CMS
 * liefert dasselbe Markup wieder und wieder. Key = raw input, Value =
 * sanitised output. Größe geclippt (LRU-ähnlich via Map-Insertion-Order).
 */
const SANITIZE_CACHE = new Map<string, string>();
const SANITIZE_CACHE_MAX = 500;

export function sanitizeUntrustedHtml(html: string): string {
  const cached = SANITIZE_CACHE.get(html);
  if (cached !== undefined) {
    // Move to end (most-recently-used).
    SANITIZE_CACHE.delete(html);
    SANITIZE_CACHE.set(html, cached);
    return cached;
  }
  const out = sanitizeHtml(html, HTML_BLOCK_OPTIONS);
  SANITIZE_CACHE.set(html, out);
  if (SANITIZE_CACHE.size > SANITIZE_CACHE_MAX) {
    // Evict oldest.
    const oldest = SANITIZE_CACHE.keys().next().value;
    if (oldest !== undefined) SANITIZE_CACHE.delete(oldest);
  }
  return out;
}

type Block = { _type?: string; html?: unknown } & Record<string, unknown>;

function isBlock(value: unknown): value is Block {
  return typeof value === 'object' && value !== null;
}

function visit(node: unknown): void {
  if (Array.isArray(node)) {
    for (const item of node) visit(item);
    return;
  }
  if (!isBlock(node)) return;

  if (node._type === 'html' && typeof node.html === 'string') {
    node.html = sanitizeUntrustedHtml(node.html);
  }

  for (const key of Object.keys(node)) {
    if (key === '_type' || key === 'html') continue;
    visit(node[key]);
  }
}

/** Mutiert den Tree in-place: alle HtmlBlocks bekommen sanitisiertes `html`. */
export function sanitizeBlocks(root: unknown): void {
  visit(root);
}