import { onErrorResumeNext } from 'botframework-webchat-core';
import MarkdownIt from 'markdown-it';
import sanitizeHTML from 'sanitize-html';

import { parseDocumentFromString, serializeDocumentIntoString } from 'botframework-webchat-component/internal';
import ariaLabel, { post as ariaLabelPost, pre as ariaLabelPre } from './markdownItPlugins/ariaLabel';
import { pre as respectCRLFPre } from './markdownItPlugins/respectCRLF';
import betterLinkDocumentMod, { BetterLinkDocumentModDecoration } from './private/betterLinkDocumentMod';
import iterateLinkDefinitions from './private/iterateLinkDefinitions';

const SANITIZE_HTML_OPTIONS = Object.freeze({
  allowedAttributes: {
    a: ['aria-label', 'class', 'href', 'name', 'rel', 'target'],
    button: ['aria-label', 'class', 'type', 'value'],
    img: ['alt', 'class', 'src', 'title'],
    span: ['aria-label']
  },
  allowedSchemes: ['data', 'http', 'https', 'ftp', 'mailto', 'sip', 'tel'],
  allowedTags: [
    'a',
    'b',
    'blockquote',
    'br',
    'button',
    'caption',
    'code',
    'del',
    'div',
    'em',
    'h1',
    'h2',
    'h3',
    'h4',
    'h5',
    'h6',
    'hr',
    'i',
    'img',
    'ins',
    'li',
    'nl',
    'ol',
    'p',
    'pre',
    's',
    'span',
    'strike',
    'strong',
    'table',
    'tbody',
    'td',
    'tfoot',
    'th',
    'thead',
    'tr',
    'ul'
  ],
  // Bug of https://github.com/apostrophecms/sanitize-html/issues/633.
  // They should not remove `alt=""` even though it is empty.
  nonBooleanAttributes: []
});

type RenderInit = Readonly<{ containerClassName?: string; externalLinkAlt?: string }>;

export default function render(
  markdown: string,
  { markdownRespectCRLF, markdownRenderHTML }: Readonly<{ markdownRespectCRLF: boolean; markdownRenderHTML?: boolean }>,
  { externalLinkAlt = '' }: RenderInit = Object.freeze({})
): string {
  const linkDefinitions = Array.from(iterateLinkDefinitions(markdown));

  const MARKDOWN_IT_INIT = Object.freeze({
    breaks: false,
    html: markdownRenderHTML ?? true,
    linkify: true,
    typographer: true,
    xhtmlOut: true
  });

  if (markdownRespectCRLF) {
    markdown = respectCRLFPre(markdown);
  }

  markdown = ariaLabelPre(markdown);

  const decorate = (href: string, textContent: string): BetterLinkDocumentModDecoration => {
    const decoration: BetterLinkDocumentModDecoration = {
      rel: 'noopener noreferrer',
      target: '_blank',
      wrapZeroWidthSpace: true
    };

    const ariaLabelSegments: string[] = [textContent];
    const classes: Set<string> = new Set();
    const linkDefinition = linkDefinitions.find(({ url }) => url === href);
    const protocol = onErrorResumeNext(() => new URL(href).protocol);

    if (linkDefinition) {
      ariaLabelSegments.push(
        linkDefinition.title || onErrorResumeNext(() => new URL(linkDefinition.url).host) || linkDefinition.url
      );

      // linkDefinition.identifier is uppercase, while linkDefinition.label is as-is.
      linkDefinition.label === textContent && classes.add('webchat__render-markdown__pure-identifier');
    }

    // For links that would be sanitized out, let's turn them into a button so we could handle them later.
    if (!SANITIZE_HTML_OPTIONS.allowedSchemes.map(scheme => `${scheme}:`).includes(protocol)) {
      decoration.asButton = true;

      classes.add('webchat__render-markdown__citation');
    } else if (protocol === 'http:' || protocol === 'https:') {
      decoration.iconAlt = externalLinkAlt;
      decoration.iconClassName = 'webchat__render-markdown__external-link-icon';

      ariaLabelSegments.push(externalLinkAlt);
    }

    // The first segment is textContent. Putting textContent is aria-label is useless.
    if (ariaLabelSegments.length > 1) {
      // If "aria-label" is already applied, do not overwrite it.
      decoration.ariaLabel = (value: string) => value || ariaLabelSegments.join(' ');
    }

    decoration.className = Array.from(classes).join(' ');

    // By default, Markdown-It will set "title" to the link title in link definition.

    // However, "title" may be narrated by screen reader:
    // - Edge
    //   - <a> will narrate "aria-label" but not "title"
    //   - <button> will narrate both "aria-label" and "title"
    // - NVDA
    //   - <a> will narrate both "aria-label" and "title"
    //   - <button> will narrate both "aria-label" and "title"

    // Title makes it very difficult to control narrations by the screen reader. Thus, we are disabling it in favor of "aria-label".
    // This will not affect our accessibility compliance but UX. We could use a non-native tooltip or other forms of visual hint.

    decoration.title = false;

    return decoration;
  };

  const htmlAfterMarkdown = ariaLabelPost(new MarkdownIt(MARKDOWN_IT_INIT).use(ariaLabel).render(markdown));

  // TODO: [P1] In some future, we should apply "better link" and "sanitization" outside of the Markdown engine.
  //       Particularly, apply them at `useRenderMarkdownAsHTML` instead of inside the default `renderMarkdown`.
  //       If web devs want to bring their own Markdown engine, they don't need to rebuild "better link" and sanitization themselves.

  const documentAfterMarkdown = parseDocumentFromString(htmlAfterMarkdown);

  betterLinkDocumentMod(documentAfterMarkdown, decorate);

  const htmlAfterBetterLink = serializeDocumentIntoString(documentAfterMarkdown);

  const htmlAfterSanitization = sanitizeHTML(htmlAfterBetterLink, SANITIZE_HTML_OPTIONS);

  return htmlAfterSanitization;
}