srveit/insteon-hub2

'use strict'
const createPlmBufferProcessor = () => {
  let previousBuffer = ''

  const processPlmBuffer = buffer => {
    const previousBufferLength = previousBuffer.length > 2
      ? parseInt(previousBuffer.slice(-2), 16)
      : 0
    const bufferLength = buffer && buffer.length > 2
      ? parseInt(buffer.slice(-2), 16)
      : 0

    if (!buffer || buffer === previousBuffer) {
      /* eslint no-undefined: "off" */
      return undefined
    }
    let chunk
    if (bufferLength >= previousBufferLength) {
      if (previousBuffer.slice(0, previousBufferLength) ===
          buffer.slice(0, previousBufferLength)) {
        // Case 1
        //   old aaaaaa000000
        //   new aaaaaabbb000
        //   Added to existing buffer but not rolled over
        chunk = buffer.slice(previousBufferLength, bufferLength)
      } else {
        // Case 3
        //   old aaaaaa000000
        //   new bbbbbbbb0000
        //   Totally new buffer
        chunk = buffer.slice(0, bufferLength)
      }
    } else if (previousBuffer.slice(bufferLength, previousBufferLength) ===
               buffer.slice(bufferLength, previousBufferLength)) {
      // Case 2
      //   old aaaaaa000000
      //   new bbbaaabbbbbb
      //   Added to existing buffer and rolled over
      chunk = buffer.slice(previousBufferLength, -2) +
        buffer.slice(0, bufferLength)
    } else {
      // Case 3
      //   old aaaaaa000000
      //   new bbb000000000
      //   Totally new buffer
      chunk = buffer.slice(0, bufferLength)
    }
    previousBuffer = buffer
    return chunk
  }

  return Object.freeze({
    processPlmBuffer,
  })
}

exports.createPlmBufferProcessor = createPlmBufferProcessor