(function () {
    window.onload = function () {
        $('#launchUrl').val('http://dr-chuck.com/ims/php-simple/tool.php');
        $('#key').val('THX1138');
        $('#secret').val('secret');
        updateLtiLaunchForm();
    };

    this.updateLtiLaunchForm = function () {
        var launchUrl = $('#launchUrl').val();
        var encodedSecret = encodeURIComponent($('#secret').val()) + '&';
        var $ltiLaunchForm = $('#ltiLaunchForm');

        $ltiLaunchForm.attr('action', launchUrl);
        $('#oauth_consumer_key').val($('#key').val());
        $('#oauth_timestamp').val(Math.floor(new Date().getTime() / 1000));
        $('#oauth_nonce').val(uniqid('', true));

        var fields = [];
        $('input[type="text"]', $ltiLaunchForm).not('[name="oauth_signature"]').each(function () {
            var input = $(this);
            fields.push(input.attr('name') + '=' + rawurlencode(input.val()));
        });

        var message = 'POST&' + encodeURIComponent(launchUrl) + '&' +
            rawurlencode(fields.sort().join('&'));

        var oauthSignature = CryptoJS.enc.Base64.stringify(CryptoJS.HmacSHA1(message, encodedSecret));
        $('#oauth_signature').val(oauthSignature);
    };

    this.rawurlencode = function (str) {
        str = (str + '').toString();
        return encodeURIComponent(str).replace(/!/g, '%21').replace(/'/g, '%27').replace(/\(/g, '%28').
            replace(/\)/g, '%29').replace(/\*/g, '%2A');
    };

    this.uniqid = function (prefix, moreEntropy) {
        prefix = prefix || '';
        moreEntropy = moreEntropy || false;
        var result;

        this.formatSeed = function (seed, width) {
            seed = parseInt(seed, 10).toString(16);
            return width < seed.length
                ? seed.slice(seed.length - width)
                : ((width > seed.length) ? new Array(1 + (width - seed.length)).join('0') + seed : seed);
        };

        result = prefix + this.formatSeed(parseInt(new Date().getTime() / 1000, 10), 8) + this.formatSeed(Math.floor(Math.random() * 0x75bcd15) + 1, 5);

        if (moreEntropy) result += (Math.random() * 10).toFixed(8).toString();

        return result;
    };
})();