// ==UserScript==
// @name         Agar Movement Keys
// @description  Use arrow keys or WASD to move. E to eject mass. T to toggle movement with mouse.
// @version      0.3
// @match        http://agar.io/
// @grant        none
// ==/UserScript==

// Get canvas and create an object with (fake) mouse position properties.
var canvas = document.getElementById("canvas");
var endPoint = {clientX: innerWidth / 2, clientY: innerHeight / 2};
var holdMoveEvent = null;

// Closure:
var handleKeys = (function() {

    // KeyCodes and an object for storing key states.
    var keys = [37, 38, 39, 40, 65, 87, 68, 83];
    var key = {left: "keyup", up: "keyup", right: "keyup", down: "keyup"};

    // Stop movement and reset center when window loses focus or is resized.
    ["blur", "resize"].forEach(function(listener) {
        window.addEventListener(listener, function() {
            key.left = key.up = key.right = key.down = "keyup";
            endPoint = {clientX: innerWidth / 2, clientY: innerHeight / 2};
            canvas.onmousedown(endPoint);
        }, false);
    });

    // The actual handleKeys function.
    return function(event, keyState) {

        // Stop if keydown is repeating.
        if (event.repeat && keyState === "keydown") return;

        // Thanks to /u/Apostolique for the toggle!
        if (event.which === 84 && keyState === "keydown") {
            if (canvas.onmousemove === null) {
                canvas.onmousemove = holdMoveEvent;
            } else {
                canvas.onmousemove = null;
            }
            return;
        }

        if (canvas.onmousemove === holdMoveEvent) return;

        // Iterate through keycodes.
        for (var i = 0; i < keys.length; i++) {

            // If keycode doesn't match, skip it.
            if (event.which !== keys[i]) continue;

            // Get axis based on key index, odd = y, even = x. Store directions (axis.dir) to be evaluated next.
            var axis = (i % 2) ? {dir: ["up", "down"], value: "clientY"} : {dir: ["left", "right"], value: "clientX"};

            // Get direction based on index and axis. If divisible by 4, direction must be up or left (depending on the axis).
            var direction = ((i % 4) === 0 || ((i - 1) % 4) === 0) ? axis.dir[0] : axis.dir[1];

            // If key state is already set, return.
            if (key[direction] === keyState) return;

            // Else, set it.
            key[direction] = keyState;

            // Positive or negative value based on key state.
            var point = (keyState === "keydown") ? 500 : -500;

            // Invert value if direction is left or up.
            point = (direction === "left" || direction === "up") ? -point : point;

            // Return true to send the movement.
            return [axis.value, point];
        }
    };
})();

// Send all key events to handleKeys.
["keydown", "keyup"].forEach(function(keyState) {
    window.addEventListener(keyState, function(event) {
        if (!canvas.onmousedown) return;
        var data = handleKeys(event, keyState);
        if (data && keyState === "keyup") {
            var fraction = data[1] / 10;
            for (var i = 0; i < 2; i++) {
                endPoint[data[0]] += (fraction * (i ? 1 : 9));
                canvas.onmousedown(endPoint);
            }
        } else if (data && keyState === "keydown") {
            endPoint[data[0]] += data[1];
            canvas.onmousedown(endPoint);
        }
        if (event.which === 87) event.stopPropagation();
        if (event.which === 69) {
            window["on" + keyState]({keyCode: 87});
        }
    }, true);
});

// Overwrites default behavior.
(function overwrite(startTime) {
    if (Date.now() - startTime > 5000) return;
    if (!canvas.onmousemove) return setTimeout(overwrite, 100, startTime);
    holdMoveEvent = canvas.onmousemove;
    canvas.onmousemove = null;
})(Date.now());