import {Injectable} from 'angular2/di';

import {global} from 'angular2/src/facade/lang';

let _nextRequestId = 0;

export const JSONP_HOME = '__ng_jsonp__';

var _jsonpConnections = null;

function _getJsonpConnections(): {[key: string]: any} {

if (_jsonpConnections === null) {

_jsonpConnections = global[JSONP_HOME] = {};

}

return _jsonpConnections;

}

// Make sure not to evaluate this in a non-browser environment!

@Injectable()

export class BrowserJsonp {

// Construct a <script> element with the specified URL

build(url: string): any {

let node = document.createElement('script');

node.src = url;

return node;

}

nextRequestID(): string { return `__req${_nextRequestId++}`; }

requestCallback(id: string): string { return `${JSONP_HOME}.${id}.finished`; }

exposeConnection(id: string, connection: any) {

let connections = _getJsonpConnections();

connections[id] = connection;

}

removeConnection(id: string) {

var connections = _getJsonpConnections();

connections[id] = null;

}

// Attach the <script> element to the DOM

send(node: any) { document.body.appendChild(<Node>(node)); }

// Remove <script> element from the DOM

cleanup(node: any) {

if (node.parentNode) {

node.parentNode.removeChild(<Node>(node));

}

}

}