bkp7 / mdprepare

  *   .start          => points at the character in the string why the other item starts (ie. comment or code block)

  *   .length         => is the overall length of the comment or code block.

  *   .internalStart  => points at the character in the string where the internal payload starts

  *   .internalLength => is the length of the internal payload

  *   .commandString  => is the command string found within the particular item

  *   .info           => is a structure containing further info about what was found

  * if start is returned as -1 then nothing was found

  *

  * The internalStart/internaLength defines the internal content which will be replaced. This does not include

  * leading and lagging CRLF/LF. So the replacement text is not required to have either leading or lagging line

  * endings. However, if the internalLength is negative this means that leading CRLF or LF must be added by the insertion

  * routine. The reason for this is that it allows insertions between code fences or mdpInsert pairs which have zero lines

  * between them.

  *

**/

const {earlierOf} = require('./helpers.js')

export function findCode (txt, start) {

  /**

  * finds the next code in the string provided starting at position start

  * returns an object containing start, length, internalStart, internalLength

  *

  * there are three types of code insertion - code span (inline), fenced code and indented code

  *

  * eg. span (1 or more backticks):

  * some text ``echo myfile.txt`` more text

  *

  * eg. indented (4 or more indent spaces):

  * some text

  *     function test() {

  *       console.log('test')

  *     }

  * more text

  *

  * eg. fenced (3 or more backticks on a row on their own)

  * some text

  * ``` js

  * function test() {

  *   console.log('test')

  * }

  * ```

  * more text

  *

  **/

  let x = _findFencedCode(txt, start)

  let y = _findIndentedCode(txt, start)

  let z = _findCodeSpan(txt, start)

  return earlierOf(x, earlierOf(y, z))

}

function _findFencedCode (txt, start) {

  // if the internalLength is returned as -1 this means that text cannot simply be inserted at the internalStart

  // location. Instead an additional preceding new line must be inserted along with the new text

  // another way to look at this is that the internal text is 1 character short

  // a value of -2 indicates a CRLF needs to be inserted

  let a = _findOpeningCodeFence(txt, start)

  if (a.start === -1) { return a }

  return _findClosingCodeFence(txt, a)

  function _findClosingCodeFence (txt, opening) {

    // updates the passed result structure with the location and type of the next closing code fence

    // to match the opening cofeFence passed in

    let regex

    let r = JSON.parse(JSON.stringify(opening)) // create copy of opening structure passed in

    regex = RegExp('(^|\r\n|\n)([ ]{0,3}> |>|[ ]{0,0})[ ]{0,3}[' + r.info.codeFence[0] + ']{' + r.info.codeFence.length + ',}[ ]*($|\r\n|\n)', 'g')

    regex.lastIndex = r.internalStart - 2

    let regexResult = regex.exec(txt)

    if (opening.info.blockQuote.length !== 0) {

      // we are in a block quote so the codeFence will end at the earlier of the found regex OR end of the block quote

      let b = _findEndOfBlock(txt, r.internalStart)

      if (b !== -1 && (regexResult === null || b < (regexResult.index + regexResult[1].length))) {

        // the block end dictates the code block end

        r.internalLength = b - r.internalStart

        r.length = b - r.start

        return r

      }

    }

    if (regexResult === null) {

      r.internalLength = txt.length - r.internalStart

      r.length = txt.length - r.start

    } else {

      r.internalLength = regexResult.index - r.internalStart

      r.length = regexResult.index + regexResult[0].length - regexResult[3].length - r.start

    }

    return r

  }

  function _findEndOfBlock (txt, start) {

    // finds the first line which is not marked as block

    let regex = /(\r\n|\n)(?!([ ]{0,3}> |>))[^>\r\n]*/g

    regex.lastIndex = start

    let regexResult = regex.exec(txt)

    if (regexResult === null) {

      return -1

    } else {

      return regexResult.index

    }

  }

}

function _findIndentedCode (txt, start) {

  let regex = /((?:^|\r\n|\n)[ ]{4,}[^\r\n\0]*){1,}/g

  regex.lastIndex = start

  let regexResult = regex.exec(txt)

  if (regexResult === null) {

    return {start: -1}

  } else {

    return {

      start: regexResult.index,

      length: regexResult[0].length,

      internalStart: regexResult.index,

      internalLength: regexResult[0].length,

      info: {indent: regexResult[2]},

      commandString: ''

    }

  }

}

function _findCodeSpan (txt, start) {

  // finds an inline Code Span in the format: 'some text ``echo myfile.txt`` more text'

  // look for start

  let lookFrom = start

  while (true) {

    let s = _findCodeSpanStart(txt, lookFrom)

    if (s.start === -1) { return s }

    // look for end

    let e = _findCodeSpanEnd(txt, s)

    if (e.start !== -1) { return e }

    lookFrom = s.internalStart

  }

  function _findCodeSpanStart (txt, start) {

    let regex = /(^|[^`])(`+)[^`]/g

    // 1st capture group is the first (or no) character prior to the identifying `'s

    // 2nd group is the ` characters (however many there are)

    regex.lastIndex = start

    let regexResult = regex.exec(txt)

    if (regexResult === null) { return {start: -1} }

    let r = {

      start: regexResult.index + regexResult[1].length,

      internalStart: regexResult.index + regexResult[1].length + regexResult[2].length,

      info: {

        codeFence: regexResult[2]

      }

    }

    return r

  }

  function _findCodeSpanEnd (txt, opening) {

    let r = JSON.parse(JSON.stringify(opening)) // create copy of opening structure passed in

    let regex = RegExp('([^`])(' + r.info.codeFence + ')($|[^`])', 'g')

    regex.lastIndex = r.internalStart

    let regexResult = regex.exec(txt)

    if (regexResult === null) { return {start: -1} }

    r.internalLength = regexResult.index + regexResult[1].length - r.internalStart

    r.length = regexResult.index + regexResult[0].length - regexResult[3].length - r.start

    r.commandString = ''

    return r

}