/*  Copyright (c) 2014, Torbjörn Lager
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

		 /*******************************
		 *	    CONSTRUCTOR		*
		 *******************************/

/**
 * Create a Prolog engine (Pengine). The constructor is handed an object
 * that specifies the behaviour. Defaults for this object may be
 * specified by adding properties to `Pengine.options`.  For example
 * `Pengine.options.chunk = 1000;`
 *
 * @param {Object} options
 * @param {String} [options.format="json"] specifies the response
 * format.
 * @param {String} [options.ask] specifies the initial Prolog query.  If
 * omitted, the user must provide an `oncreate` handler and use
 * `.ask()` from the create handle.
 * @param {Boolean} [options.destroy=true] If `true` destroy the pengine
 * if initial query has finished.
 * @param {Int} [options.chunk=1] Provide answers in chunks of this
 * size.
 * @param {String} [options.applicatio="pengine_sandbox"] Application in
 * which to execute the query.
 * @param {Function} [options.oncreate]
 * @param {Function} [options.onsuccess]
 * @param {Function} [options.ondata]
 * @param {Function} [options.onfailure]
 * @param {Function} [options.onerror]
 * @param {Function} [options.onprompt]
 * @param {Function} [options.onoutput]
 * @param {Function} [options.ondebug]
 * @param {Function} [options.onping]
 * @param {Function} [options.onabort]
 * @param {Function} [options.ondestroy]
 * Callback functions.  The callback function is called with an object
 * argument.  This object always has a property `pengine` that refers
 * to the JavaScript `Pengine` instance.  All callbacks are optional,
 * although creating a Pengine without `onsuccess` or `ondata` is
 * typically meaningless.
 *
 * On success, first `options.onsuccess` is called.  If this does not
 * return `false` and `options.ondata` is defined, this function is
 * called for each answer in the answer set with `this` refering to
 * the data object as a whole while the first argument is an object
 * holding a single answer.  If more answers are available, `next()`
 * is called on the Pengine.
 */

function Pengine(options) {
  var that = this;

  // private functions
  function fillDefaultOptions(options) {
    for(var k in Pengine.options) {
      if ( Pengine.options.hasOwnProperty(k) &&
	   options[k] === undefined )
	options[k] = Pengine.options[k];
    }

    return options;
  }

  function copyOptions(to, from, list) {
    for(var i=0; i<list.length; i++) {
      var k = list[i];
      if ( from[k] !== undefined )
	to[k] = from[k];
    }
  }

  // initialize network support in browser
  if (typeof Pengine.network === "undefined") { 
    Pengine.network = $;  // assume jQuery initialized by now
    $(window).on("beforeunload", function() {
      Pengine.destroy_all();
    });
  }

  // create instance
  this.options = fillDefaultOptions(options);
  this.id = null;

  // On creation
  var src = this.options.src ? [this.options.src] : [];
  var createOptions = {
    src_text: this.script_sources(src).join('\n')
  };

  copyOptions(createOptions, options,
	      [ "format",
		"application",
		"ask",
		"template",
		"chunk",
		"destroy"
	      ]);

  this.request =
  Pengine.network.ajax(this.options.server + '/create',
	 { contentType: "application/json; charset=utf-8",
	   dataType: "json",
	   data: JSON.stringify(createOptions),
	   type: "POST",
	   success: function(obj) {
	     that.process_response(obj);
	   },
	   error: function(jqXHR, textStatus, errorThrown) {
	     that.error(jqXHR, textStatus, errorThrown);
	   },
	   complete: function() {
	     that.request = undefined;
	   }
	 });

}/*end of Pengine()*/


		 /*******************************
		 *	     METHODS		*
		 *******************************/

(function() {
Pengine.alive = [];

/**
 * Default options for `new Pengine()`
 */
Pengine.options = {
  format: "json",
  server: "/pengine"
};

/**
 * Ask Prolog to execute a query. May also be specified as an option
 * when creating the Pengine.
 * @param {String} query is the Prolog query in Prolog syntax.  Use
 * `Pengine.stringify()` when constructing the query from JavaScript
 * data.
 * @param {Object} [options] provides additional options.  The option
 * values must be valid Prolog.  For example, `{chunk: 10}`.
 */
Pengine.prototype.ask = function(query, options) {
  this.send('ask((' + query + '), ' + options_to_list(options) + ')');
};

/**
 * Ask for more results.  May be called from the `onsuccess` callback
 * if `obj.more` equals `true`
 * @param {Int} n is the chunk-size for the next chunk of answers.
 */
Pengine.prototype.next = function(n) {
  if ( n === undefined )
    this.send('next');
  else
    this.send('next('+n+')');
};

/**
 * Ask the pengine to stop.  May be called from the `onsuccess` callback
 * if `obj.more` equals `true`
 */
Pengine.prototype.stop = function() {
  this.send('stop');
};

/**
 * Respond with a value after the pengines `onprompt` callback has been
 * called.
 */
Pengine.prototype.respond = function(input) {
  this.send('input((' + input + '))');
};

/**
 * Abort the pengine.  May be called at any time.
 */
Pengine.prototype.abort = function() {
  var pengine = this;

  if ( this.request ) {
    this.request.pengine_aborted = true;
    this.request.abort();
  }
  var url = this.options.server + '/abort' +
    '?id=' + encodeURIComponent(this.id) +
    '&format=' + encodeURIComponent(this.options.format);
  this.request = Pengine.network.get(url,
	function(obj) {
	  pengine.process_response(obj);
	}).fail(function(jqXHR, textStatus, errorThrown) {
	  pengine.error(jqXHR, textStatus, errorThrown);
	}).always(function() {
	  pengine.request = undefined;
	});
};

/**
 * Ping the status of the pengine.
 * @param {Number} [interval] If `undefined`, send a single ping.  If
 * > 0, set/change periodic ping event, if 0, clear periodic interval.
 */
Pengine.prototype.ping = function(interval) {
  var pengine = this;

  if ( interval == undefined ) {
    if ( this.id ) {				/* Might not be there yet */
      var url = this.options.server + '/ping' +
        '?id=' + encodeURIComponent(this.id) +
        '&format=' + encodeURIComponent(this.options.format);
      Pengine.network.get(url,
	    function(obj) {
	      pengine.process_response(obj);
	    }).fail(function(jqXHR, textStatus, errorThrown) {
	      pengine.error(jqXHR, textStatus, errorThrown);
	    });
    }
  } else {
    if ( pengine.pingid )
      clearInterval(pengine.pingid);
    if ( interval > 0 )
      pengine.pingid = setInterval(function() {
	pengine.ping();
      }, interval);
    else
      delete pengine.pingid;
  }
};

/**
 * Destroy the pengine. May be called at any time.
 */
Pengine.prototype.destroy = function() {
  if ( !this.died ) {
    this.died = true;
    this.send('destroy');
  }
};

// internal methods

/**
 * Process the reply to a `pull_response`.  If the last answer was
 * final, this question will be asked to a death pengine.  We do not
 * consider this an error.
 */
Pengine.prototype.pull_response = function() {
  var pengine = this;

  var url = this.options.server + '/pull_response' +
    '?id=' + encodeURIComponent(this.id) +
    '&format=' + encodeURIComponent(this.options.format);
  this.request = Pengine.network.get(url,
	function(obj) {
	  if ( obj.event !== 'died')
	    pengine.process_response(obj);
	}).fail(function(jqXHR, textStatus, errorThrown) {
	  pengine.error(jqXHR, textStatus, errorThrown);
	}).always(function() {
	  pengine.request = undefined;
	});
};

/**
 * Invoke `/pengine/send`.  This method takes three parameters: the
 * reply format (one of `prolog` or `json`), the pengine id (a UUID)
 * and the event (a serialized Prolog term).  In old versions, this
 * was sent as a GET request.  This is undesirable, both because GET
 * assumes a side-effect-free operation and because of the size limit
 * to URLs imposed by some infrastructure.  The current version passes
 * the format and id as URL parameters and the content as a POST body.
 *
 * Future versions might use the HTTP Accept header intead of format
 * and add the id to the URL, i.e., using `/pengine/send/ID`
 */
Pengine.prototype.send = function(event) {
  var pengine = this;

  var url = pengine.options.server +
		'/send?format=' + encodeURIComponent(this.options.format) +
		'&id=' + encodeURIComponent(this.id);
  this.request = Pengine.network.ajax({ type: "POST",
	   url: url,
	   data: event + " .\n",
	   contentType: "application/x-prolog; charset=UTF-8",
	   success: function(obj) {
	     pengine.process_response(obj);
	   },
	   error: function(jqXHR, textStatus, errorThrown) {
	     pengine.error(jqXHR, textStatus, errorThrown);
	   },
	   complete: function() {
	     pengine.request = undefined;
	   }
         });
};

Pengine.prototype.script_sources = function(src) {
  if (typeof document === 'undefined') {
    return src;
  }
  var scripts = document.getElementsByTagName('script');

  src = src||[];
  for (var i = 0; i < scripts.length; i++) {
    if (scripts[i].getAttribute('type') == 'text/x-prolog') {
      src.push(scripts[i].textContent);
    }
  }

  return src;
};

Pengine.prototype.process_response = function(response) {
  // Processes response coming from either jQuery or najax.
  // najax does not parse JSON automatically.
  var obj = typeof response === 'string' ? JSON.parse(response) : response;
  obj.pengine = this;
  Pengine.onresponse[obj.event].call(this, obj);
};

Pengine.prototype.callback = function(f, obj) {
  if ( this.options[f] )
    return this.options[f].call(obj, obj);
  return "not implemented";
};

/**
 * Called on AJAX interaction error.  Unfortunately, we have little
 * information.  Is this error permanent?  If so, we should unregister
 * the pengine.  If not, we could just report the error and allow the
 * application to retry.
 */

Pengine.prototype.error = function(jqXHR, textStatus, errorThrown) {
  if ( jqXHR.pengine_aborted )
    return;

  var obj = { event:"error", pengine:this };

  if ( jqXHR.responseText ) {
    var msg = jqXHR.responseText.replace(/[^]*<body[^>]*>/, "")
				.replace(/<\/body>/, "");
    var plain;
    if (typeof $ === 'undefined') {
      plain = msg.replace(/(<([^>]+)>)/ig, '');
    } else {
      plain = $("<div></div>").html(msg).text();
    }
    obj.data = plain;
    obj.dataHTML = msg;
  } else if ( textStatus )
  { obj.data = "Server status: " + textStatus;
  } else if ( errorThrown )
  { obj.data = "Server error: " + errorThrown;
  }
  if ( !obj.dataHTML && obj.data )
    obj.dataHTML = '<span class="error">'+obj.data+'</span>';

  unregisterPengine(this);		/* see above */

  this.process_response(obj);
}


Pengine.prototype.report = function(level, data) {
  if ( console !== undefined )
    console[level](data);
  else if ( level === 'error' )
    alert(data);
};


		 /*******************************
		 *	  HANDLE EVENTS		*
		 *******************************/

Pengine.onresponse = {
  create: function(obj) {
    this.id = obj.id;
    Pengine.alive.push(this);

    if ( Pengine.alive.length > obj.slave_limit ) {
      this.destroy();
      obj.data = "Attempt to create too many pengines. "+
		 "The limit is: " + obj.slave_limit;
      obj.code = "too_many_pengines";
      if ( !this.callback('onerror', obj) )
	this.report('error', obj.data);
    } else {
      this.callback('oncreate', obj);
      if ( obj.answer )
	this.process_response(obj.answer);
    }
  },

  stop:    function(obj) { this.callback('onstop',    obj); },
  failure: function(obj) { this.callback('onfailure', obj); },
  prompt:  function(obj) { this.callback('onprompt',  obj); },

  success: function(obj) {
    if ( this.callback('onsuccess', obj) != false &&
	 this.options.ondata ) {
      for(i=0; i<obj.data.length; i++) {
	this.options.ondata.call(obj, obj.data[i]);
      }
      if ( obj.more )
	obj.pengine.next();
    }
  },

  error: function(obj) {
    if ( obj.code == "existence_error" &&
	 obj.arg1 == "pengine" &&
	 obj.arg2 == this.id )
      unregisterPengine(this);

    if ( this.callback('onerror', obj) == "not implemented" )
      this.report('error', obj.data);
  },

  output: function(obj) {
    if ( !this.id )
      this.id = obj.id;
    this.callback('onoutput', obj);
    this.pull_response();
  },

  ping: function(obj) {
    this.callback('onping', obj);
  },

  debug: function(obj) {
    if ( this.callback('ondebug', obj) == "not implemented" )
      this.report('log', obj.data);
    this.pull_response();
  },

  abort: function(obj) {
    this.aborted = true;
    this.callback('onabort', obj);
  },

  destroy: function(obj) {
    unregisterPengine(this);
    if ( obj.data )
      this.process_response(obj.data);
    this.callback('ondestroy', obj);
  },

  died: function(obj) {
    unregisterPengine(this);
    if ( !this.aborted ) {
      obj.data = "Pengine has died";
      obj.code = "died";
      if ( !this.callback('onerror', obj) )
	this.report('error', obj.data);
    }
  }
};


		 /*******************************
		 *	PRIVATE FUNCTIONS	*
		 *******************************/

function unregisterPengine(pengine) {
  if ( pengine.pingid ) {
    clearInterval(pengine.pingid);
    delete pengine.pingid;
  }

  var index = Pengine.alive.indexOf(pengine);
  if ( index > -1 )
    Pengine.alive.splice(index, 1);

  pengine.died = true;
}

/**
 * Turn an object into a Prolog option list.  The option values
 * must be valid Prolog syntax.  Use Pengine.stringify() when
 * applicable.
 */
function options_to_list(options) {
  var opts = "[";
  for (var name in options) {
    if ( opts !== "[" )
      opts += ",";
    if ( options.hasOwnProperty(name) ) {
      opts += name + "(" + options[name] + ")";
    }
  }
  return opts + "]";
}

})();

/**
 * Serialize JavaScript data as a Prolog term.  The serialization
 * is performed according to the rules below:
 *
 *   - A number is serialized trivially
 *   - A string is serialized into a Prolog string unless
 *     `option.string == "atom"`
 *   - `true`, `false`, `null` and `undefined` are serialized as
 *     atoms.
 *   - An array is serialized into a Prolog list
 *   - An object is serialized into a Prolog dict.  Keys that are
 *     integers are mapped to Prolog integers, other keys are mapped
 *     to Prolog atoms.  Note that in JavaScript {1:42} and {"1":42}
 *     are equavalent and both can be retrieved as either
 *     obj[1] or obj["1"]
 *
 * @param  {any} data is the data to be serialized
 * @param  {Object} [options]
 * @param {String} [options.string] If `"atom"`, translate
 * JavaScript strings into Prolog objects.
 * @return {String|undefined} is the Prolog serialization of `data`
 */

Pengine.stringify = function(data, options) {
  var msg  = "";
  var strq = options && options.string == "atom" ? "'" : '"';

  function serialize(data) {
    function stringEscape(s, q) {
      function dec2unicode(i)
      { var r;
	if      (i >= 0    && i <= 15)    { r = "\\u000" + i.toString(16); }
	else if (i >= 16   && i <= 255)   { r = "\\u00"  + i.toString(16); }
	else if (i >= 256  && i <= 4095)  { r = "\\u0"   + i.toString(16); }
	else if (i >= 4096 && i <= 65535) { r = "\\u"    + i.toString(16); }
	return r
      }

      var result = q;
      for(var i=0; i<s.length; i++) {
	var c = s.charAt(i);
	if ( c >= ' ' ) {
	       if ( c == '\\' ) result += "\\\\";
	  else if ( c ==   q  ) result += "\\"+q;
	  else result += c;
	} else {
	       if ( c == '\n' ) result += "\\n";
	  else if ( c == '\r' ) result += "\\r";
	  else if ( c == '\t' ) result += "\\t";
	  else if ( c == '\b' ) result += "\\b";
	  else if ( c == '\f' ) result += "\\f";
	  else result += dec2unicode(c.charCodeAt(0));
	}
      }
      return result+q;
    }

    function serializeKey(k) {
      if ( k.match(/^\d+$/) ) {
	msg += k;
      } else {
	msg += stringEscape(k, "'");
      }

      return true;
    }

    switch ( typeof(data) ) {
      case "boolean":
	msg += data ? "true" : "false";
        break;
      case "undefined":
	msg += "undefined";
	break;
      case "number":
	msg += data;
	break;
      case "string":
	msg += stringEscape(data, strq);
	break;
      case "object":
	if ( data == null ) {
	  msg += "null";
	} else if ( Array.isArray(data) ) {
	  msg += "[";
	  for(var i=0; i<data.length; i++) {
	    if ( !serialize(data[i]) )
	      return false;
	    if ( i+1 < data.length )
	      msg += ",";
	  }
	  msg += "]";
	} else {
	  var first = true;
	  msg += "js{";
	  for(var p in data) {
	    if ( data.hasOwnProperty(p) ) {
	      if ( !first )
		msg += ",";
	      else
		first = false;
	      if ( !serializeKey(p) )
		return false;
	      msg += ":";
	      if ( !serialize(data[p]) )
		return false;
	    }
	  }
	  msg += "}";
	}
	break;
      default:
	return false;
    }

    return true;
  }

  if ( serialize(data) )
    return msg;
}/*end of Pengine.stringify*/


		 /*******************************
		 *	    DESTRUCTION		*
		 *******************************/

/**
 * Destroy all living pengines.  This is called on page unload.  Note
 * that the pengines may live on different servers.
 */
Pengine.destroy_all = function(async) {
  if ( Pengine.alive.length > 0 ) {
    var servers = {};

    for(var i=0; i<Pengine.alive.length; i++) {
      var pengine = Pengine.alive[i];
      var server = pengine.options.server;

      if ( servers[server] )
	servers[server].push(pengine.id);
      else
	servers[server] = [pengine.id];
    }

    Pengine.alive = [];

    for(var server in servers) {
      if ( servers.hasOwnProperty(server) ) {
	Pengine.network.ajax({ url:server + '/destroy_all?ids=' + servers[server],
	         async: async === undefined ? true : false,
		 timeout: 1000
	       });
      }
    }
  }
};

if (typeof window === 'undefined') {
  // Node.js
  module.exports = Pengine;
  var najax = require('najax');
  Pengine.network = najax;
  Pengine.network.ajax = najax;
}
