urbit/outside/commonmark/js/ansi/newlines.js

/**
 * Accepts any node Stream instance and hijacks its "write()" function,
 * so that it can count any newlines that get written to the output.
 *
 * When a '\n' byte is encountered, then a "newline" event will be emitted
 * on the stream, with no arguments. It is up to the listeners to determine
 * any necessary deltas required for their use-case.
 *
 * Ex:
 *
 *   var cursor = ansi(process.stdout)
 *     , ln = 0
 *   process.stdout.on('newline', function () {
 *    ln++
 *   })
 */

/**
 * Module dependencies.
 */

var assert = require('assert')
var NEWLINE = '\n'.charCodeAt(0)

function emitNewlineEvents (stream) {
  if (stream._emittingNewlines) {
    // already emitting newline events
    return
  }

  var write = stream.write

  stream.write = function (data) {
    // first write the data
    var rtn = write.apply(stream, arguments)

    if (stream.listeners('newline').length > 0) {
      var len = data.length
        , i = 0
      // now try to calculate any deltas
      if (typeof data == 'string') {
        for (; i<len; i++) {
          processByte(stream, data.charCodeAt(i))
        }
      } else {
        // buffer
        for (; i<len; i++) {
          processByte(stream, data[i])
        }
      }
    }

    return rtn
  }

  stream._emittingNewlines = true
}
module.exports = emitNewlineEvents


/**
 * Processes an individual byte being written to a stream
 */

function processByte (stream, b) {
  assert.equal(typeof b, 'number')
  if (b === NEWLINE) {
    stream.emit('newline')
  }
}