var EventEmitter = require('events').EventEmitter,
    queryString = require('query-string');

function tryParseJson(data){
    try{
        return JSON.parse(data);
    }catch(error){
        return error;
    }
}

function timeout(){
   this.request.abort();
   this.emit('timeout');
}

function Ajax(settings){
    var queryStringData,
        ajax = this;

    if(typeof settings === 'string'){
        settings = {
            url: settings
        };
    }

    if(typeof settings !== 'object'){
        settings = {};
    }

    ajax.settings = settings;
    ajax.request = new XMLHttpRequest();
    ajax.settings.method = ajax.settings.method || 'get';

    if(ajax.settings.cors && !'withCredentials' in ajax.request){
        if (typeof XDomainRequest !== 'undefined') {
            // XDomainRequest only exists in IE, and is IE's way of making CORS requests.
            ajax.request = new XDomainRequest();
        } else {
            // Otherwise, CORS is not supported by the browser.
            ajax.emit('error', new Error('Cors is not supported by this browser'));
        }
    }

    if(ajax.settings.cache === false){
        ajax.settings.data = ajax.settings.data || {};
        ajax.settings.data._ = new Date().getTime();
    }

    if(ajax.settings.method.toLowerCase() === 'get' && typeof ajax.settings.data === 'object'){
        var urlParts = ajax.settings.url.split('?');

        queryStringData = queryString.parse(urlParts[1]);

        for(var key in ajax.settings.data){
            queryStringData[key] = ajax.settings.data[key];
        }

        var parsedQueryStringData = queryString.stringify(queryStringData);

        ajax.settings.url = urlParts[0] + (parsedQueryStringData ? '?' + parsedQueryStringData : '');
        ajax.settings.data = null;
    }

    ajax.request.addEventListener('progress', function(event){
        ajax.emit('progress', event);
    }, false);

    ajax.request.addEventListener('load', function(event){
        var data = event.target.responseText;

        if(ajax.settings.dataType && ajax.settings.dataType.toLowerCase() === 'json'){
            if(data === ''){
                data = undefined;
            }else{
                data = tryParseJson(data);
                if(data instanceof Error){
                    ajax.emit('error', event, data);
                    return;
                }
            }
        }

        if(event.target.status >= 400){
            ajax.emit('error', event, data);
        } else {
            ajax.emit('success', event, data);
        }

    }, false);

    ajax.request.addEventListener('error', function(event){
        ajax.emit('error', event);
    }, false);

    ajax.request.addEventListener('abort', function(event){
        ajax.emit('error', event, new Error('Connection Aborted'));
        ajax.emit('abort', event);
    }, false);

    ajax.request.addEventListener('loadend', function(event){
        clearTimeout(ajax._requestTimeout);
        ajax.emit('complete', event);
    }, false);

    ajax.request.open(ajax.settings.method || 'get', ajax.settings.url, true);

    if(ajax.settings.cors && 'withCredentials' in ajax.request) {
        ajax.request.withCredentials = !!settings.withCredentials;
    }

    // Set default headers
    if(ajax.settings.contentType !== false){
        ajax.request.setRequestHeader('Content-Type', ajax.settings.contentType || 'application/json; charset=utf-8');
    }
    if(ajax.settings.requestedWith !== false) {
        ajax.request.setRequestHeader('X-Requested-With', ajax.settings.requestedWith || 'XMLHttpRequest');
    }
    if(ajax.settings.auth){
        ajax.request.setRequestHeader('Authorization', ajax.settings.auth);
    }

    // Set custom headers
    for(var headerKey in ajax.settings.headers){
        ajax.request.setRequestHeader(headerKey, ajax.settings.headers[headerKey]);
    }

    if(ajax.settings.processData !== false && ajax.settings.dataType === 'json'){
        ajax.settings.data = JSON.stringify(ajax.settings.data);
    }
}

Ajax.prototype = Object.create(EventEmitter.prototype);

Ajax.prototype.send = function(){
    var ajax = this;

    ajax._requestTimeout = setTimeout(
        function(){
            timeout.apply(ajax, []);
        },
        ajax.settings.timeout || 120000
    );

    ajax.request.send(ajax.settings.data && ajax.settings.data);
};

module.exports = Ajax;