/* classe API */
function API(target){ this.target = target; }

API.prototype = {
	xhr: [],                         // tableau d'objets pour les requêtes ajax
	buffer: null,                    // Contiendra le buffer pour debugger si erreur de parsage
	error: {                         // error constants
		'-1': 'Invalid target format: "METHOD module/method"',
		'-2': 'XHR error',
		'-3': 'Invalid JSON response',
	},

	/* transaction avec le serveur (http://{host}/api/)
	*
	* @param pTarget<String>		URI cible, format "HTTP_METHOD uri/uri/uri"
	* @param pArgs<Object>			Le tableu d'arguments passé en POST (attribut<->postfield) à http://{host}/api/
	* @param pHandler<Function>		Fonction qui s'éxécutera lors de la réponse (1 argument -> réponse<Object>)
	* @param pToken<String>			Optionnel, token d'auth pour l'api
	*
	***************************************************************************************************
	*
	* @usecase
	*	1.		api.call(
	*	2.			"PUT newspaper/article/4"
	*	2.			{ content: "New article content" },
	*	3.			function(resp){
	*	4.				alert(resp.error);
	*	5.			}
	*	6.		);
	*
	*/
	call: function(pTarget, pArgs, pHandler, pToken=null){


		/* (1) Check @pHandler (for dispatching errors)
		---------------------------------------------------------*/
		/* (1) Check if is a Function */
		if( !(pHandler instanceof Function) )
			throw new Error("3rd argument must be a function, but is of type '"+typeof(pHandler)+"' !");



		/* (2) Check @pTarget
		---------------------------------------------------------*/
		/* (1) Check format */
		if( !/^([A-Z]+) (.+)/i.test(pTarget) ){
			pHandler({ error: -1, ErrorDescription: this.error['-1'] });
			return false;
		}

		/* (2) Store locally data */
		var lHttpMethod = RegExp.$1;
		var lUri        = RegExp.$2;



		/* (3) Create form data
		---------------------------------------------------------*/
		/* (1) Create virtual form */
		var lForm = new FormData();

		/* (2) Add attributes */
		for( var key in pArgs ){

			// {2.1} If a file -> send as it //
			if( pArgs[key] instanceof File )
				lForm.append(key, pArgs[key]);

			// {2.2} Else -> JSON stringify //
			else
				lForm.append(key, JSON.stringify(pArgs[key]));

		}



		/* (4) Create XHR request
		---------------------------------------------------------*/
		/* (1) Clean ended requests */
		for( var i = this.xhr.length-1 ; i >= 0 ; i-- ){

			if( this.xhr[i] != null )
				break;

			this.xhr.pop();

		}

		/* (2) Push a new entry -> fetch its index */
		i = this.xhr.push(null) - 1;

		/* (3) Create XHR object */
		this.xhr[i] = (window.XMLHttpRequest) ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHttpRequest');



		/* (5) Bind response event
		---------------------------------------------------------*/
		var self = this; // to access the buffer

		this.xhr[i].onreadystatechange = function(i){

			/* (1) If request over */
			if( this.xhr[i].readyState == 4 ){

				/* (2) Update buffer (for debug) */
				self.buffer = this.xhr[i].responseText;

				/* (3) If request success */
				if( [0, 200, 417].indexOf(this.xhr[i].status) > -1 ){


					/* (3.1) Create default response (if JSON error) */
					var response = {error:-3, ErrorDescription: self.error['-3']};

					/* (3.2) Try to parse JSON */
					try{ response = JSON.parse(this.xhr[i].responseText); }catch(e){}

					/* (3.3) Launch @pHandler with response */
					pHandler(response);

				/* (4) If request error */
				}else
					pHandler({ error:-2, ErrorDescription: self.error['-2'] });

				/* (5) Notify current xhr instance is done */
				this.xhr[i] = null;

			}

		}.bind(this, i);


		/* (6) Finish & send request
		---------------------------------------------------------*/
		/* (1) Open the XHR */
		this.xhr[i].open(lHttpMethod, this.target+lUri, true);

		/* (2) Manage optional token */
		if( pToken != null )
			this.xhr[i].setRequestHeader('Authorization', 'Digest '+pToken);

		/* (3) Custom header to notify we're using Ajax */
		this.xhr[i].setRequestHeader('X-Requested-With', 'XMLHttpRequest');

		/* (4) Make the call */
		this.xhr[i].send( lForm );

		return true;

	}
};