// $X
// 
// usage:
// 
// $X(aExpression);
// $X(aExpression, aContext, aType);
// $X(aExpression, aContext, aType, aResolver, aNamespaceHash);
// $X(aNamespaceHash, aResolver, aType, aContext, aExpression);
// 
// or
// 
// $X()
// .setExpression(aXPathExpression)  // XPath expression
// .setCotext(aContext)              // to use relative XPath
// .setType(aType)                   // type of result (*1)
// .setNamespace(aNamespaceHash)     // namespace hash (*2)
// .setResolver(aResolver)           // function. high priority than NamespaceHash
// .setDocument(aDocument)           // base document
// .setDefault(aExpression, aContext, aType, aResolver, aNamespaceHash) // same as $X() arguments
// .evaluate();
// 
// or
// 
// var $x = $X().setDocument(aDocument).setNamespace(aNamespaceHash).getX();
// $x(aExpression, aContext, aType);
 
 
// *1 type of result example
// 
// var aType = Number  // return Number
// var aType = Boolean // return Boolean
// var aType = String  // return String
// var aType = Array   // return Array
// 
// *2 namespace hash example
// 
// var aNamespaceHash = {
//   h:        "http://www.w3.org/1999/xhtml"
//   , rdf:    "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
//   , grddl:  "http://www.w3.org/2003/g/data-view#"
// }
 
function $X(){
	function XPath(){return (this instanceof XPath) ? this : new XPath()}
	XPath.prototype = {
	    evaluate: function(){
		var self = this;
		var doc = this.doc || 
		    (window.content && window.content.document) || // for Addons
		    document.ownerDocument || 
		    document;
		var context = this.context || doc;
		var resolver = this.resolver || function(prefix){
		    if(doc.contentType == "text/html") return ""; // text/html need no namespace uri
		    return (self.namespace[prefix] ||
			    ((doc.contentType == "application/xhtml+xml") && "http://www.w3.org/1999/xhtml") ||
			    doc.createNSResolver(context.documentElement).lookupNamespaceURI(prefix) ||
			    doc.documentElement.namespaceURI);
		}
		var exp = doc.createExpression(this.expression, resolver);
		switch (this.type) {
		case String:
		    return exp.evaluate(
			context,
			XPathResult.STRING_TYPE,
			null
		    ).stringValue;
		case Number:
		    return exp.evaluate(
			context,
			XPathResult.NUMBER_TYPE,
			null
		    ).numberValue;
		case Boolean:
		    return exp.evaluate(
			context,
			XPathResult.BOOLEAN_TYPE,
			null
		    ).booleanValue;
		case Array:
		    var result = exp.evaluate(
			context,
			XPathResult.ORDERED_NODE_SNAPSHOT_TYPE,
			null
		    );
		    var ret = [];
		    for (var i = 0, len = result.snapshotLength; i < len; ret.push(result.snapshotItem(i++)));
		    return ret;
		case undefined:
		    var result = exp.evaluate(context, XPathResult.ANY_TYPE, null);
		    switch (result.resultType) {
		    case XPathResult.STRING_TYPE : return result.stringValue;
		    case XPathResult.NUMBER_TYPE : return result.numberValue;
		    case XPathResult.BOOLEAN_TYPE: return result.booleanValue;
		    case XPathResult.UNORDERED_NODE_ITERATOR_TYPE: {
			// not ensure the order.
			var ret = [];
			var i;
			while ((i = result.iterateNext())) {
			    ret.push(i);
			}
			return ret;
		    }
		    }
		    return null;
		default:
		    throw(TypeError("$X: specified type is not valid type."));
		}
	    },
 
	    setExpression: function(arg){
		this.expression = arg;
		return this;
	    },
 
	    setContext: function(arg){
		this.context = arg;
		return this;
	    },
 
	    setType: function(arg){
		this.type = arg;
		return this;
	    },
 
	    setResolver: function(arg){
		this.resolver = arg;
		return this;
	    },
 
	    setNamespace: function(arg){
		this.namespace = arg;
		return this;
	    },
 
	    setDocument: function(arg){
		this.doc = arg;
		return this;
	    },
 
	    checkArgumentType: function(o){
		return (((o == String  || 
			  o == Number  ||
			  o == Boolean ||
			  o == Array) &&
			 'type') ||
			((typeof o == 'string') && 'expression') ||
			((o instanceof Function) && 'resolver') ||
			((o instanceof Node) && 'context') ||
			((o instanceof Object) && 'namespace')
		       );
	    },
	    setDefault: function(args){ // args is Array. e.g. setDefault(['//div', context, Array])
		var self = this;
		args = Array.slice(args);
		args.forEach(function(o){
				 var a = self.checkArgumentType(o);
				 if(a) self[a] = o;
			     });
		return this;
	    },
 
	    getX: function(){
		var self = this;
		return function(){
		    if(arguments.length == 0) return self;
		    return self.setDefault(arguments).evaluate();
		}
	    }
	}
	if(arguments.length == 0) return XPath();
	return XPath()
	.setDefault(arguments)
	.evaluate();
}