Swap-Aggregator-Subgraph/node_modules/pull-stream/sinks/drain.js

'use strict'

module.exports = function drain (op, done) {
  var read, abort

  function sink (_read) {
    read = _read
    if(abort) return sink.abort()
    //this function is much simpler to write if you
    //just use recursion, but by using a while loop
    //we do not blow the stack if the stream happens to be sync.
    ;(function next() {
        var loop = true, cbed = false
        while(loop) {
          cbed = false
          read(null, function (end, data) {
            cbed = true
            if(end = end || abort) {
              loop = false
              if(done) done(end === true ? null : end)
              else if(end && end !== true)
                throw end
            }
            else if(op && false === op(data) || abort) {
              loop = false
              read(abort || true, done || function () {})
            }
            else if(!loop){
              next()
            }
          })
          if(!cbed) {
            loop = false
            return
          }
        }
      })()
  }

  sink.abort = function (err, cb) {
    if('function' == typeof err)
      cb = err, err = true
    abort = err || true
    if(read) return read(abort, cb || function () {})
  }

  return sink
}