const MarkdownIt = require("markdown-it")

/** @typedef {import('markdownlint').RuleParams} MarkdownLintRuleParams */
/** @typedef {import('markdownlint').MarkdownItToken} MarkdownItToken */

/**
 * Calls the provided function for each matching token.
 *
 * @param {MarkdownLintRuleParams} params RuleParams instance.
 * @param {string} type Token type identifier.
 * @param {(token: MarkdownItToken) => void} handler Callback function.
 * @returns {void}
 */
const filterTokens = (params, type, handler) => {
  for (const token of params.tokens) {
    if (token.type === type) {
      handler(token)
    }
  }
}

/**
 * Converts a Markdown heading into an HTML fragment according to the rules
 * used by GitHub.
 *
 * @see https://github.com/DavidAnson/markdownlint/blob/d01180ec5a014083ee9d574b693a8d7fbc1e566d/lib/md051.js#L1
 * @param {string} inlineText Inline token for heading.
 * @returns {string} Fragment string for heading.
 */
const convertHeadingToHTMLFragment = (inlineText) => {
  return (
    "#" +
    encodeURIComponent(
      inlineText
        .toLowerCase()
        // RegExp source with Ruby's \p{Word} expanded into its General Categories
        // https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb
        // https://ruby-doc.org/core-3.0.2/Regexp.html
        .replace(
          /[^\p{Letter}\p{Mark}\p{Number}\p{Connector_Punctuation}\- ]/gu,
          "",
        )
        .replace(/ /gu, "-"),
    )
  )
}

const headingTags = new Set(["h1", "h2", "h3", "h4", "h5", "h6"])
const ignoredTokens = new Set(["heading_open", "heading_close"])

/**
 * Gets the headings from a Markdown string.
 * @param {string} content
 * @returns {string[]}
 */
const getMarkdownHeadings = (content) => {
  const markdownIt = new MarkdownIt({ html: true })
  const tokens = markdownIt.parse(content, {})

  /** @type {string[]} */
  const headings = []

  /** @type {string | null} */
  let headingToken = null

  for (const token of tokens) {
    if (headingTags.has(token.tag)) {
      if (token.type === "heading_open") {
        headingToken = token.markup
      } else if (token.type === "heading_close") {
        headingToken = null
      }
    }

    if (ignoredTokens.has(token.type)) {
      continue
    }

    if (headingToken === null) {
      continue
    }

    const children = token.children ?? []

    headings.push(
      `${children
        .map((token) => {
          return token.content
        })
        .join("")}`,
    )
  }

  return headings
}

module.exports = {
  filterTokens,
  convertHeadingToHTMLFragment,
  getMarkdownHeadings,
}