var Readable = require('readable-stream').Readable;
var inherits = require('inherits');

module.exports = from2;

from2.ctor = ctor;
from2.obj = obj;

var Proto = ctor();

function toFunction(list) {
  list = list.slice();
  return function (_, cb) {
    var err = null;
    var item = list.length ? list.shift() : null;
    if (item instanceof Error) {
      err = item;
      item = null;
    }

    cb(err, item);
  };
}

function from2(opts, read) {
  if (typeof opts !== 'object' || Array.isArray(opts)) {
    read = opts;
    opts = {};
  }

  var rs = new Proto(opts);
  rs._from = Array.isArray(read) ? toFunction(read) : read || noop;
  return rs;
}

function ctor(opts, read) {
  if (typeof opts === 'function') {
    read = opts;
    opts = {};
  }

  opts = defaults(opts);

  inherits(Class, Readable);
  function Class(override) {
    if (!(this instanceof Class)) return new Class(override);
    this._reading = false;
    this._callback = check;
    this.destroyed = false;
    Readable.call(this, override || opts);

    var self = this;
    var hwm = this._readableState.highWaterMark;

    function check(err, data) {
      if (self.destroyed) return;
      if (err) return self.destroy(err);
      if (data === null) return self.push(null);
      self._reading = false;
      if (self.push(data)) self._read(hwm);
    }
  }

  Class.prototype._from = read || noop;
  Class.prototype._read = function (size) {
    if (this._reading || this.destroyed) return;
    this._reading = true;
    this._from(size, this._callback);
  };

  Class.prototype.destroy = function (err) {
    if (this.destroyed) return;
    this.destroyed = true;

    var self = this;
    process.nextTick(function () {
      if (err) self.emit('error', err);
      self.emit('close');
    });
  };

  return Class;
}

function obj(opts, read) {
  if (typeof opts === 'function' || Array.isArray(opts)) {
    read = opts;
    opts = {};
  }

  opts = defaults(opts);
  opts.objectMode = true;
  opts.highWaterMark = 16;

  return from2(opts, read);
}

function noop() {}

function defaults(opts) {
  opts = opts || {};
  return opts;
}