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 {findCode} = require('./findCode.js')

export function findMdpInsert (txt, start) {

  let s = _findMdpStartUnfenced(txt, start)

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

  let s1 = JSON.parse(JSON.stringify(s)) // create copy

  let depth = 1

  let e

  let posn = s1.internalStart - 2

  while (depth !== 0) {

    e = _findMdpEndUnfenced(txt, s, posn)

    if (e.start === -1) {

      // we have not found any more ends so we need to return a fail

      return e

    }

    s1 = _findMdpStartUnfenced(txt, posn)

    if (s1.start !== -1) {

      // we have found another start pattern

      if (s1.start < (e.internalStart + e.internalLength)) {

        depth++

        posn = s1.internalStart - 2

      } else {

        depth--

        posn = e.start + e.length

      }

    } else {

      depth--

      posn = e.start + e.length

    }

    if (depth > 5) { return {start: -1} }

  }

}

function _findMdpEndUnfenced (txt, opening, start) {

  let lookFrom = start

  let m, c

  while (true) {

    m = _findMdpEnd(txt, opening, lookFrom - 2)

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

    // we need to find the first code which ends after the mdpEnd starts

    c = _findCodeEndingAfter(txt, lookFrom, (m.internalStart + m.internalLength))

    if (c.start === -1 || (m.internalStart + m.internalLength) < c.start) { break } // the mdp end we've found is not within a code fence

    // the mdp end we've found is within a code fence so find the next one

    lookFrom = c.start + c.length

  }

  return m

  function _findMdpEnd (txt, opening, start) {

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

    let regex = /(\r\n|\n)([ ]{0,3}\[<[^\r\n\t\0[\]]*\]: #)(\r\n|\n|$)/g

    regex.lastIndex = start

    let regexResult = regex.exec(txt)

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

    r.internalLength = regexResult.index - r.internalStart

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

    return r

  }

}

function _findCodeEndingAfter (txt, start, endingAfter) {

  // returns the first code block which ends after the position specified

  // the search starts at start

  let pos = start

  let c

  do {

    c = findCode(txt, pos)

    pos = c.start + c.length

  } while (c.start !== -1 && pos <= endingAfter)

  return c

}