define([], function () {
    var Util = {};

    // If once is true, after the event has been fired, any further handlers which are
    // registered will fire immediately, and this type of event cannot be fired twice.
    Util.mkEvent = function (once) {
        var handlers = [];
        var fired = false;
        return {
            reg: function (cb) {
                if (once && fired) { return void setTimeout(cb); }
                handlers.push(cb);
            },
            unreg: function (cb) {
                if (handlers.indexOf(cb) === -1) { throw new Error("Not registered"); }
                handlers.splice(handlers.indexOf(cb), 1);
            },
            fire: function () {
                if (fired) { return; }
                fired = true;
                var args = Array.prototype.slice.call(arguments);
                handlers.forEach(function (h) { h.apply(null, args); });
            }
        };
    };

    Util.find = function (map, path) {
        return (map && path.reduce(function (p, n) {
            return typeof(p[n]) !== 'undefined' && p[n];
        }, map));
    };

    Util.uid = function () {
        return Number(Math.floor(Math.random() * Number.MAX_SAFE_INTEGER))
            .toString(32).replace(/\./g, '');
    };

    Util.fixHTML = function (str) {
        if (!str) { return ''; }
        return str.replace(/[<>&"']/g, function (x) {
            return ({ "<": "&lt;", ">": "&gt", "&": "&amp;", '"': "&#34;", "'": "&#39;" })[x];
        });
    };

    Util.hexToBase64 = function (hex) {
        var hexArray = hex
            .replace(/\r|\n/g, "")
            .replace(/([\da-fA-F]{2}) ?/g, "0x$1 ")
            .replace(/ +$/, "")
            .split(" ");
        var byteString = String.fromCharCode.apply(null, hexArray);
        return window.btoa(byteString).replace(/\//g, '-').replace(/=+$/, '');
    };

    Util.base64ToHex = function (b64String) {
        var hexArray = [];
        atob(b64String.replace(/-/g, '/')).split("").forEach(function(e){
            var h = e.charCodeAt(0).toString(16);
            if (h.length === 1) { h = "0"+h; }
            hexArray.push(h);
        });
        return hexArray.join("");
    };

    Util.uint8ArrayToHex = function (a) {
        // call slice so Uint8Arrays work as expected
        return Array.prototype.slice.call(a).map(function (e) {
            var n = Number(e & 0xff).toString(16);
            if (n === 'NaN') {
                throw new Error('invalid input resulted in NaN');
            }

            switch (n.length) {
                case 0: return '00'; // just being careful, shouldn't happen
                case 1: return '0' + n;
                case 2: return n;
                default: throw new Error('unexpected value');
            }
        }).join('');
    };

    Util.deduplicateString = function (array) {
        var a = array.slice();
        for(var i=0; i<a.length; i++) {
            for(var j=i+1; j<a.length; j++) {
                if(a[i] === a[j]) { a.splice(j--, 1); }
            }
        }
        return a;
    };

    Util.getHash = function () {
        return window.location.hash.slice(1);
    };

    Util.replaceHash = function (hash) {
        if (window.history && window.history.replaceState) {
            if (!/^#/.test(hash)) { hash = '#' + hash; }
            void window.history.replaceState({}, window.document.title, hash);
            if (typeof(window.onhashchange) === 'function') {
                window.onhashchange();
            }
            return;
        }
        window.location.hash = hash;
    };

    /*
     *  Saving files
     */
    Util.fixFileName = function (filename) {
        return filename.replace(/ /g, '-').replace(/[\/\?]/g, '_')
            .replace(/_+/g, '_');
    };

    var oneKilobyte = 1024;
    var oneMegabyte = 1024 * oneKilobyte;
    var oneGigabyte = 1024 * oneMegabyte;

    Util.bytesToGigabytes = function (bytes) {
        return Math.ceil(bytes / oneGigabyte * 100) / 100;
    };

    Util.bytesToMegabytes = function (bytes) {
        return Math.ceil(bytes / oneMegabyte * 100) / 100;
    };

    Util.bytesToKilobytes = function (bytes) {
        return Math.ceil(bytes / oneKilobyte * 100) / 100;
    };

    Util.magnitudeOfBytes = function (bytes) {
        if (bytes >= oneGigabyte) { return 'GB'; }
        else if (bytes >= oneMegabyte) { return 'MB'; }
    };

    Util.fetch = function (src, cb) {
        var done = false;
        var CB = function (err, res) {
            if (done) { return; }
            done = true;
            cb(err, res);
        };

        var xhr = new XMLHttpRequest();
        xhr.open("GET", src, true);
        xhr.responseType = "arraybuffer";
        xhr.onload = function () {
            if (/^4/.test(''+this.status)) {
                return CB('XHR_ERROR');
            }
            return void CB(void 0, new Uint8Array(xhr.response));
        };
        xhr.send(null);
    };

    Util.throttle = function (f, ms) {
        var to;
        var g = function () {
            window.clearTimeout(to);
            to = window.setTimeout(f, ms);
        };
        return g;
    };

    /*  takes a function (f) and a time (t) in ms. returns a function wrapper
        which prevents the internal function from being called more than once
        every t ms. if the function is prevented, returns time til next valid
        execution, else null.
    */
    Util.notAgainForAnother = function (f, t) {
        if (typeof(f) !== 'function' || typeof(t) !== 'number') {
            throw new Error("invalid inputs");
        }
        var last = null;
        return function () {
            var now = +new Date();
            if (last && now <= last + t) { return t - (now - last); }
            last = now;
            f();
            return null;
        };
    };

    Util.createRandomInteger = function () {
        return Math.floor(Math.random() * Number.MAX_SAFE_INTEGER);
    };

    Util.getAppType = function () {
        var parts = window.location.pathname.split('/')
            .filter(function (x) { return x; });
        if (!parts[0]) { return ''; }
        return parts[0];
    };

    /* for wrapping async functions such that they can only be called once */
    Util.once = function (f) {
        var called;
        return function () {
            if (called) { return; }
            called = true;
            f.apply(this, Array.prototype.slice.call(arguments));
        };
    };

    Util.slice = function (A) {
        return Array.prototype.slice.call(A);
    };

    return Util;
});