/**
The MIT License

Copyright (c) 2008 Marcus Westin marcus@narcvs.com

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
// Marcus Westin marcus@narcvs.com
function fingerprintForm(id) {
	// Get our form
	var form = document.getElementById(id);

	// Create hidden form element for storing the fingerprint
	var fingerprint = document.createElement('input');
	fingerprint.type = 'hidden';
	fingerprint.name = 'fingerprint';
	fingerprint.id = 'fingerprint';
	fingerprint.value = '';
	form.appendChild(fingerprint);

	// Find the password input field
	var inputs = form.getElementsByTagName('input');
	var password;
	for (var i=0; i < inputs.length; i++) {
		if (inputs[i].type == 'password') {
			password = inputs[i];
		}
	}
	
	// When the password field is empty, reset the fingerprint timestamps. 
	// This captures "select all text, and replace by typing," which otherwise gets lost
	var oldOnkeydown = password.onkeydown;
	password.onkeydown = function(e) {
		if (password.value.length == 0) {
			t0 = Number(new Date())
			fingerprint.value = 0;			
		}
		return oldOnkeydown ? oldOnkeydown(e) : e;
	}
	// Start monitoring passworn keypress events
	var oldOnkeypress = password.onkeypress;
	password.onkeypress = function(e) {
		if (password.value.length > 0) {
			fingerprint.value += ',' + (Number(new Date()) - t0)
		}
		return oldOnkeypress ? oldOnkeypress(e) : e;
	}
};

// <form id="login-form"> ... </form>
// Usage - fingerprint('login-form')