;(function($){
  var zepto = $.zepto, oldQsa = zepto.qsa, oldMatches = zepto.matches

  function visible(elem){
    elem = $(elem)
    return !!(elem.width() || elem.height()) && elem.css("display") !== "none"
  }

  // Implements a subset from:
  // http://api.jquery.com/category/selectors/jquery-selector-extensions/
  //
  // Each filter function receives the current index, all nodes in the
  // considered set, and a value if there were parentheses. The value
  // of `this` is the node currently being considered. The function returns the
  // resulting node(s), null, or undefined.
  //
  // Complex selectors are not supported:
  //   li:has(label:contains("foo")) + li:has(label:contains("bar"))
  //   ul.inner:first > li
  var filters = $.expr[':'] = {
    visible:  function(){ if (visible(this)) return this },
    hidden:   function(){ if (!visible(this)) return this },
    selected: function(){ if (this.selected) return this },
    checked:  function(){ if (this.checked) return this },
    parent:   function(){ return this.parentNode },
    first:    function(idx){ if (idx === 0) return this },
    last:     function(idx, nodes){ if (idx === nodes.length - 1) return this },
    eq:       function(idx, _, value){ if (idx === value) return this },
    contains: function(idx, _, text){ if ($(this).text().indexOf(text) > -1) return this },
    has:      function(idx, _, sel){ if (zepto.qsa(this, sel).length) return this }
  }

  var filterRe = new RegExp('(.*):(\\w+)(?:\\(([^)]+)\\))?$\\s*'),
      childRe  = /^\s*>/,
      classTag = 'Zepto' + (+new Date())

  function process(sel, fn) {
    // quote the hash in `a[href^=#]` expression
    sel = sel.replace(/=#\]/g, '="#"]')
    var filter, arg, match = filterRe.exec(sel)
    if (match && match[2] in filters) {
      var filter = filters[match[2]], arg = match[3]
      sel = match[1]
      if (arg) {
        var num = Number(arg)
        if (isNaN(num)) arg = arg.replace(/^["']|["']$/g, '')
        else arg = num
      }
    }
    return fn(sel, filter, arg)
  }

  zepto.qsa = function(node, selector) {
    return process(selector, function(sel, filter, arg){
      try {
        var taggedParent
        if (!sel && filter) sel = '*'
        else if (childRe.test(sel))
          // support "> *" child queries by tagging the parent node with a
          // unique class and prepending that classname onto the selector
          taggedParent = $(node).addClass(classTag), sel = '.'+classTag+' '+sel

        var nodes = oldQsa(node, sel)
      } catch(e) {
        console.error('error performing selector: %o', selector)
        throw e
      } finally {
        if (taggedParent) taggedParent.removeClass(classTag)
      }
      return !filter ? nodes :
        zepto.uniq($.map(nodes, function(n, i){ return filter.call(n, i, nodes, arg) }))
    })
  }

  zepto.matches = function(node, selector){
    return process(selector, function(sel, filter, arg){
      return (!sel || oldMatches(node, sel)) &&
        (!filter || filter.call(node, null, arg) === node)
    })
  }
})(Zepto)