thematic-break.js

/**
 * @import {
 *   Code,
 *   Construct,
 *   State,
 *   TokenizeContext,
 *   Tokenizer
 * } from 'micromark-util-types'
 */

import {ok as assert} from 'devlop'
import {factorySpace} from 'micromark-factory-space'
import {markdownLineEnding, markdownSpace} from 'micromark-util-character'
import {codes, constants, types} from 'micromark-util-symbol'

/** @type {Construct} */
export const thematicBreak = {
  name: 'thematicBreak',
  tokenize: tokenizeThematicBreak
}

/**
 * @this {TokenizeContext}
 *   Context.
 * @type {Tokenizer}
 */
function tokenizeThematicBreak(effects, ok, nok) {
  let size = 0
  /** @type {NonNullable<Code>} */
  let marker

  return start

  /**
   * Start of thematic break.
   *
   * ```markdown
   * > | ***
   *     ^
   * ```
   *
   * @type {State}
   */
  function start(code) {
    effects.enter(types.thematicBreak)
    // To do: parse indent like `markdown-rs`.
    return before(code)
  }

  /**
   * After optional whitespace, at marker.
   *
   * ```markdown
   * > | ***
   *     ^
   * ```
   *
   * @type {State}
   */
  function before(code) {
    assert(
      code === codes.asterisk ||
        code === codes.dash ||
        code === codes.underscore,
      'expected `*`, `-`, or `_`'
    )
    marker = code
    return atBreak(code)
  }

  /**
   * After something, before something else.
   *
   * ```markdown
   * > | ***
   *     ^
   * ```
   *
   * @type {State}
   */
  function atBreak(code) {
    if (code === marker) {
      effects.enter(types.thematicBreakSequence)
      return sequence(code)
    }

    if (
      size >= constants.thematicBreakMarkerCountMin &&
      (code === codes.eof || markdownLineEnding(code))
    ) {
      effects.exit(types.thematicBreak)
      return ok(code)
    }

    return nok(code)
  }

  /**
   * In sequence.
   *
   * ```markdown
   * > | ***
   *     ^
   * ```
   *
   * @type {State}
   */
  function sequence(code) {
    if (code === marker) {
      effects.consume(code)
      size++
      return sequence
    }

    effects.exit(types.thematicBreakSequence)
    return markdownSpace(code)
      ? factorySpace(effects, atBreak, types.whitespace)(code)
      : atBreak(code)
  }
}