html.js

const HTMLMap = {
  '&': '&',
  '<': '&lt;',
  '>': '&gt;',
}

/**
 * @param {String} c
 * @returns {String}
 */
const escapeHTMLChar = (c) => HTMLMap[c] ?? c

/**
 *
 * @param {String} name
 * @param {Object} params
 * @returns
 */
function tag(name, params) {
  return {
    open: params
      ? `<${name} ${Object.entries(params)
          .map(
            ([key, value]) =>
              `${key}="${value.replace(/[<&"]/g, escapeHTMLChar)}"`,
          )
          .join(' ')}>`
      : `<${name}>`,
    close: `</${name}>`,
  }
}

const HTMLTags = {
  bold: tag('b'),
  italic: tag('i'),
  code: tag('code'),
  pre: tag('pre'),
  strikethrough: tag('s'),
  underline: tag('u'),
  text_link: ({ url }) => tag('a', { href: url }),
  text_mention: ({ user }) => tag('a', { href: `tg://user?id=${user.id}` }),
}

/**
 *
 * @param {import('node-telegram-bot-api').MessageEntity} entity
 * @returns
 */
function getHTMLTag(entity) {
  const tag = HTMLTags[entity.type || 'unknown']
  if (!tag) return { open: '', close: '' }
  return typeof tag === 'function' ? tag(entity) : tag
}

/**
 *
 * @param {String} text
 * @param {import('node-telegram-bot-api').MessageEntity[]} entities
 */
const formatHTML = (text = '', entities = []) => {
  const chars = ['', ...text, ''].map(escapeHTMLChar)

  entities.forEach((entity) => {
    const tag = getHTMLTag(entity)
    const openPos = entity.offset
    const closePos = entity.offset + entity.length + 1
    chars[openPos] += tag.open
    chars[closePos] = tag.close + chars[closePos]
  })

  return chars.join('')
}

module.exports = { getHTMLTag, HTMLTags, escapeHTMLChar, tag, formatHTML }