import TurndownService from 'turndown';
import { gfm } from 'turndown-plugin-gfm';

import { markdownToHtml } from './MarkdownView';

// Matched to the dialect the generator writes, so a save is not a rewrite.
const turndown = new TurndownService({
  headingStyle: 'atx',
  hr: '---',
  bulletListMarker: '-',
  codeBlockStyle: 'fenced',
  fence: '```',
  emDelimiter: '*',
  strongDelimiter: '**',
  linkStyle: 'inlined',
});

// Tables, strikethrough and task lists.
turndown.use(gfm);

// Turndown pads list markers to four columns ("-   item"); the generator
// writes "- item", so the default would rewrite every bullet on first save.
turndown.addRule('tightListItem', {
  filter: 'li',
  replacement: (content, node, options) => {
    const body = content
      .replace(/^\n+/, '')
      .replace(/\n+$/, '\n')
      // Continuation lines line up under the text, not under the marker.
      .replace(/\n/g, '\n  ');
    const parent = node.parentNode as HTMLElement | null;
    let prefix = `${options.bulletListMarker} `;
    if (parent && parent.nodeName === 'OL') {
      const start = Number(parent.getAttribute('start') ?? 1);
      const index = Array.prototype.indexOf.call(parent.children, node);
      prefix = `${(Number.isFinite(start) ? start : 1) + index}. `;
    }
    const trailing = node.nextSibling && !/\n$/.test(body) ? '\n' : '';

    return prefix + body + trailing;
  },
});

// Tiptap emits `<li data-checked>`; turndown's GFM rule only knows the
// `<input type=checkbox>` shape, so without this a checklist loses its ticks.
turndown.addRule('tiptapTaskItem', {
  filter: node =>
    node.nodeName === 'LI' && node.getAttribute('data-type') === 'taskItem',
  replacement: (_content, node) => {
    const element = node as HTMLElement;
    const checked = element.getAttribute('data-checked') === 'true';
    const text = (element.textContent ?? '').trim();

    return `- [${checked ? 'x' : ' '}] ${text}\n`;
  },
});

export const markdownToEditorHtml = (markdown: string): string => {
  if (!markdown || typeof markdown !== 'string') return '';

  return markdownToHtml(markdown);
};

export const htmlToMarkdown = (html: string): string => {
  if (!html || typeof html !== 'string') return '';

  return (
    turndown
      .turndown(html)
      // An empty paragraph can leave three or more newlines behind.
      .replace(/\n{3,}/g, '\n\n')
      .trim()
  );
};