// Copyright 2014 Joyent, Inc.  All rights reserved.

var EventEmitter = require('events').EventEmitter;
var util = require('util');

var assert = require('assert-plus');

var dn = require('../dn');
var messages = require('../messages/index');
var Protocol = require('../protocol');
var PagedControl = require('../controls/paged_results_control.js');


///--- API


/**
 * Handler object for paged search operations.
 *
 * Provided to consumers in place of the normal search EventEmitter it adds the
 * following new events:
 * 1. page      - Emitted whenever the end of a result page is encountered.
 *                If this is the last page, 'end' will also be emitted.
 *                The event passes two arguments:
 *                1. The result object (similar to 'end')
 *                2. A callback function optionally used to continue the search
 *                   operation if the pagePause option was specified during
 *                   initialization.
 * 2. pageError - Emitted if the server does not support paged search results
 *                If there are no listeners for this event, the 'error' event
 *                will be emitted (and 'end' will not be).  By listening to
 *                'pageError', a successful search that lacks paging will be
 *                able to emit 'end'.
 * 3. search    - Emitted as an internal event to trigger another client search.
 */
function SearchPager(opts) {
  assert.object(opts);
  assert.func(opts.callback);
  assert.number(opts.pageSize);

  EventEmitter.call(this, {});

  this.callback = opts.callback;
  this.controls = opts.controls;
  this.pageSize = opts.pageSize;
  this.pagePause = opts.pagePause;

  this.controls.forEach(function (control) {
    if (control.type === PagedControl.OID) {
      // The point of using SearchPager is not having to do this.
      // Toss an error if the pagedResultsControl is present
      throw new Error('redundant pagedResultControl');
    }
  });

  this.finished = false;
  this.started = false;

  var emitter = new EventEmitter();
  emitter.on('searchEntry', this.emit.bind(this, 'searchEntry'));
  emitter.on('end', this._onEnd.bind(this));
  emitter.on('error',  this._onError.bind(this));
  this.childEmitter = emitter;
}
util.inherits(SearchPager, EventEmitter);
module.exports = SearchPager;

/**
 * Start the paged search.
 */
SearchPager.prototype.begin = function begin() {
  // Starting first page
  this._nextPage(null);
};

SearchPager.prototype._onEnd = function _onEnd(res) {
  var self = this;
  var cookie = null;
  res.controls.forEach(function (control) {
    if (control.type === PagedControl.OID) {
      cookie = control.value.cookie;
    }
  });
  // Pass a noop callback by default for page events
  var nullCb = function () { };

  if (cookie === null) {
    // paged search not supported
    this.finished = true;
    this.emit('page', res, nullCb);
    var err = new Error('missing paged control');
    err.name = 'PagedError';
    if (this.listeners('pageError').length > 0) {
      this.emit('pageError', err);
      // If the consumer as subscribed to pageError, SearchPager is absolved
      // from deliverying the fault via the 'error' event.  Emitting an 'end'
      // event after 'error' breaks the contract that the standard client
      // provides, so it's only a possibility if 'pageError' is used instead.
      this.emit('end', res);
    } else {
      this.emit('error', err);
      // No end event possible per explaination above.
    }
    return;
  }

  if (cookie.length === 0) {
    // end of paged results
    this.finished = true;
    this.emit('page', nullCb);
    this.emit('end', res);
  } else {
    if (this.pagePause) {
      // Wait to fetch next page until callback is invoked
      // Halt page fetching if called with error
      this.emit('page', res, function (err) {
        if (!err) {
          self._nextPage(cookie);
        } else {
          // the paged search has been canceled so emit an end
          self.emit('end', res);
        }
      });
    } else {
      this.emit('page', res, nullCb);
      this._nextPage(cookie);
    }
  }
};

SearchPager.prototype._onError = function _onError(err) {
  this.finished = true;
  this.emit('error', err);
};

/**
 * Initiate a search for the next page using the returned cookie value.
 */
SearchPager.prototype._nextPage = function _nextPage(cookie) {
  var controls = this.controls.slice(0);
  controls.push(new PagedControl({
    value: {
      size: this.pageSize,
      cookie: cookie
    }
  }));

  this.emit('search', controls, this.childEmitter,
      this._sendCallback.bind(this));
};

/**
 * Callback provided to the client API for successful transmission.
 */
SearchPager.prototype._sendCallback = function _sendCallback(err, res) {
  if (err) {
    this.finished = true;
    if (!this.started) {
      // EmitSend error during the first page, bail via callback
      this.callback(err, null);
    } else {
      this.emit('error', err);
    }
  } else {
    // search successfully send
    if (!this.started) {
      this.started = true;
      // send self as emitter as the client would
      this.callback(null, this);
    }
  }
};