Angularjs using a factory properly - html

Question

I was wondering if you could help.
I have the below code which sets a timeout delay before making a http request. The watch is bound to a input box. This is currently in my controller and it works.
$scope.$watch('query.keyword',function($http){
var searchInput = document.getElementById('searchInput').value;
var minLength = 3;
var req;
if (timeout) {
clearTimeout(timeout);
}
timeout = setTimeout(function(){
var newValue = searchInput;
if(newValue !== null && newValue.length > minLength) {
window.alert(newValue);
req = {
method: 'SET',
url: ''
};
}
}, 3000);
return $http(req);
});
Now I want this as a factory/service to call upon rather than listing it in my controller.
I then made this...
app.factory('sendSearchData', function($http) {
var searchInput = document.getElementById('searchInput').value;
var minLength = 3;
var req = null;
if (timeout) {
clearTimeout(timeout);
}
timeout = setTimeout(function(){
var newValue = searchInput;
if(newValue !== null && newValue.length > minLength) {
window.alert(newValue);
req = {
method: 'SET',
url: 'haha.php'
};
}
}, 3000);
return function() {
if($http !== null) {
return $http(req);
} else { return 0; }
};
});
Not sure if the return is right, as the previous return was flagging up a http null error.
So to use it I've done a few variations of the below code in my controller.
$scope.$watch('query.keyword', sendSearchData.success());
But I am having no luck and it's refusing to render.
Can anyone help?