var Selector = Class.create();
Selector.prototype = {
  initialize: function(expression) {
    this.params = {classNames: []};
    this.expression = expression.toString().strip();
    this.parseExpression();
    this.compileMatcher();
  },

  parseExpression: function() {
    function abort(message) { throw 'Parse error in selector: ' + message; }

    if (this.expression == '')  abort('empty expression');

    var params = this.params, expr = this.expression, match, modifier, clause, rest;
    while (match = expr.match(/^(.*)\[([a-z0-9_:-]+?)(?:([~\|!]?=)(?:"([^"]*)"|([^\]\s]*)))?\]$/i)) {
      params.attributes = params.attributes || [];
      params.attributes.push({name: match[2], operator: match[3], value: match[4] || match[5] || ''});
      expr = match[1];
    }

    if (expr == '*') return this.params.wildcard = true;
    
    while (match = expr.match(/^([^a-z0-9_-])?([a-z0-9_-]+)(.*)/i)) {
      modifier = match[1], clause = match[2], rest = match[3];
      switch (modifier) {
        case '#':       params.id = clause; break;
        case '.':       params.classNames.push(clause); break;
        case '':
        case undefined: params.tagName = clause.toUpperCase(); break;
        default:        abort(expr.inspect());
      }
      expr = rest;
    }
    
    if (expr.length > 0) abort(expr.inspect());
  },

  buildMatchExpression: function() {
    var params = this.params, conditions = [], clause;

    if (params.wildcard)
      conditions.push('true');
    if (clause = params.id)
      conditions.push('element.readAttribute("id") == ' + clause.inspect());
    if (clause = params.tagName)
      conditions.push('element.tagName.toUpperCase() == ' + clause.inspect());
    if ((clause = params.classNames).length > 0)
      for (var i = 0, length = clause.length; i < length; i++)
        conditions.push('element.hasClassName(' + clause[i].inspect() + ')');
    if (clause = params.attributes) {
      clause.each(function(attribute) {
        var value = 'element.readAttribute(' + attribute.name.inspect() + ')';
        var splitValueBy = function(delimiter) {
          return value + ' && ' + value + '.split(' + delimiter.inspect() + ')';
        }
        
        switch (attribute.operator) {
          case '=':       conditions.push(value + ' == ' + attribute.value.inspect()); break;
          case '~=':      conditions.push(splitValueBy(' ') + '.include(' + attribute.value.inspect() + ')'); break;
          case '|=':      conditions.push(
                            splitValueBy('-') + '.first().toUpperCase() == ' + attribute.value.toUpperCase().inspect()
                          ); break;
          case '!=':      conditions.push(value + ' != ' + attribute.value.inspect()); break;
          case '':
          case undefined: conditions.push('element.hasAttribute(' + attribute.name.inspect() + ')'); break;
          default:        throw 'Unknown operator ' + attribute.operator + ' in selector';
        }
      });
    }

    return conditions.join(' && ');
  },

  compileMatcher: function() {
    this.match = new Function('element', 'if (!element.tagName) return false; \
      element = $(element); \
      return ' + this.buildMatchExpression());
  },

  findElements: function(scope) {
    var element;

    if (element = $(this.params.id))
      if (this.match(element))
        if (!scope || Element.childOf(element, scope))
          return [element];

    scope = (scope || document).getElementsByTagName(this.params.tagName || '*');

    var results = [];
    for (var i = 0, length = scope.length; i < length; i++)
      if (this.match(element = scope[i]))
        results.push(Element.extend(element));

    return results;
  },

  toString: function() {
    return this.expression;
  }
}

Object.extend(Selector, {
  matchElements: function(elements, expression) {
    var selector = new Selector(expression);
    return elements.select(selector.match.bind(selector)).map(Element.extend);
  },
  
  findElement: function(elements, expression, index) {
    if (typeof expression == 'number') index = expression, expression = false;
    return Selector.matchElements(elements, expression || '*')[index || 0];
  },
  
  findChildElements: function(element, expressions) {
    return expressions.map(function(expression) {
      return expression.match(/[^\s"]+(?:"[^"]*"[^\s"]+)*/g).inject([null], function(results, expr) {
        var selector = new Selector(expr);
        return results.inject([], function(elements, result) {
          return elements.concat(selector.findElements(result || element));
        });
      });
    }).flatten();
  }
});

function $$() {
  return Selector.findChildElements(document, $A(arguments));
}