index.coffee

async = require 'async'

module.exports = (model, query, itrFunc, options, cb) ->

  if typeof options == "function"
    cb = options
    options = {}

  options.snapshot ||= true
  options.lean ||= false
  options.select ||= false

  stream = model.find(query).select(options.select).snapshot(options.snapshot).lean(options.lean).stream()

  if options.batch
    batch = []
    addToBatch = (item, callback) ->
      batch.push item
      if batch.length is options.batch
        completeBatch = batch
        batch = []
        itrFunc completeBatch, callback
      else
        callback()
    queue = async.queue addToBatch, options.concurrency or 100
  else
    queue = async.queue itrFunc, options.concurrency or 100

  queue.saturated = -> stream.pause()
  queue.empty = -> stream.resume()

  stream.on 'data', (doc) ->
    queue.push doc

  stream.on 'error', cb

  stream.on 'close', ->
    stream.resume()

    done = () ->
      if options.batch and batch.length != 0
          itrFunc batch, cb
        else
          cb()

    if queue.idle()
      return done()

    queue.drain = ->
      done()