Flowsnake = function($el, width, height, order) {
    this.$el = $el;
    this.width = width;
    this.height = height;
    this.order = order;
    this.init();
    return this;
};
Flowsnake.prototype = {
    a: 'a-b--b+a++aa+b-',
    b: '+a-bb--b-a++a+b',
    init: function() {
        this.pointer = 0;
        this.rule = this.a;
        this.x = this.width / 2;
        this.y = this.height;
        this.angle = 0;
        this.rows = [];
        function fillrow(len) {
            var str = [];
            for (var i = 0; i < len; i++) {
                str.push(' ');
            }
            return str.join('');
        }
        for (var i = 0; i < this.height; i++) {
            this.rows.push(fillrow(this.width));
        }
        for (var i = 0; i < this.order; i++) {
            this.rule = this.rule.replace(/a/g, 'x').replace(/b/g, 'y').replace(/x/g, this.a).replace(/y/g, this.b);
        }
    },
    putc: function(x, y, c) {
        function replacec(str, pos, c) {
            return str.substr(0, pos) + c + str.substr(pos + c.length);
        }
        if (x >= 0 && x < this.width && y >= 0 && y < this.height) {
            this.rows[y] = replacec(this.rows[y], x, c);
        }
    },
    line: function() {
        switch (this.angle) {
            case 0:
                this.putc(this.x, this.y, '__');
                this.x += 2;
                break;
            case 60:
                this.putc(this.x, this.y, '/');
                this.x++;
                this.y--;
                break;
            case 120:
                this.x--;
                this.putc(this.x, this.y, '\\');
                this.y--;
                break;
            case 180:
                this.x -= 2;
                this.putc(this.x, this.y, '__');
                break;
            case 240:
                this.x--;
                this.y++;
                this.putc(this.x, this.y, '/');
                break;
            case 300:
                this.y++;
                this.putc(this.x, this.y, '\\');
                this.x++;
                break;
        }
    },
    step: function(visible) {
        var redraw = false;
        switch (this.rule[this.pointer]) {
            case 'a':
            case 'b':
                this.line();
                redraw = true;
                break;
            case '-':
                this.angle = (this.angle + 60 + 360) % 360;
                break;
            case '+':
                this.angle = (this.angle - 60 + 360) % 360;
                break;
        }
        if (this.pointer < this.rule.length) {
            this.pointer++;
        }
        if (visible) {
            if (redraw) {
                this.draw();
            } else {
                this.step(visible);
            }
        }
    },
    draw: function() {
        this.$el.text(this.rows.join('\n'));
    }
};