(function(window, document) {
    var mis = [];
    var explosions = [];
    var buildings = [];
    var canv,ctx;
    var rng;
    var loopInterval;
    var missileInterval;
    var keyList = [];
    var running = false;
    var code = [38, 38, 40, 40, 37, 39, 37, 39, 65, 66];

    var missileRate = 0.3;
    var targetFPS = 30;
    var incSpeed = 2;
    var outSpeed = 6;
    var explodeDuration = 40;
    var explodeRadius = 70;

    function start() {
        setupContext();
        setupGame();
        running = true;
    }

    function setupContext() {
        canv = document.createElement('canvas');
        ctx = canv.getContext('2d');
        canv.setAttribute('style', 'position: fixed; width: 100%; height: 100%; top: 0; bottom: 0; left: 0; right: 0; cursor: crosshair; opacity: 0.75; z-index: 1000;');
        document.body.appendChild(canv);
        window.addEventListener('resize', handleResize);
        handleResize();
    }

    function seed(s) {
        return function () {
            var x = Math.sin(s++) * 10000;
            return x - Math.floor(x);
        };
    }

    function handleResize() {
        canv.width = window.innerWidth;
        canv.height = window.innerHeight;
    }

    function handleKey(evt) {
        switch(evt.keyCode) {
            case 27:
                close();
        }
        if (!running) {
            keyList.push(evt.keyCode);
            if (keyList.length > 10) {
                keyList.shift();
            }
            if (codeMatch()) {
                start();
            }
        }
    }

    function codeMatch() {
        for (var i = 0; i < 10; i++) {
            if (code[i] != keyList[i]) {
                return false;
            }
        }
        return true;
    }

    function setupGame() {
        rng = seed(Math.floor(Math.random() * 10000));
        mis = [];
        explosions = [];
        buildings = [];

        missileInterval = setInterval(() => {
            mis.push(makeMissile(rng() * canv.width, 0, rng() * canv.width, canv.height, incSpeed, false));
        }, 1000 / missileRate);
        loopInterval = setInterval(loop, 1000 / targetFPS);

        canv.addEventListener('click', evt => {
            mis.push(makeMissile(canv.width / 2, canv.height, evt.x, evt.y, outSpeed, true));
        });

        for (var i = 0; i < 6; i++) {
            buildings.push(makeBuilding(i/6));
        }
    }

    function close() {
        if (!running) return;
        clearInterval(missileInterval);
        clearInterval(loopInterval);
        document.body.removeChild(canv);
        window.removeEventListener('resize', handleResize);
        running = false;
    }

    function loop() {
        ctx.fillStyle = 'black';
        ctx.fillRect(0, 0, canv.width, canv.height);
        renderMissiles();
        renderBuildings();
        renderExplosions();
    }

    function renderMissiles() {
        for (var i = 0; i < mis.length; i++) {
            var m = mis[i];
            m.t++;
            var cx = m.sx + m.vx * m.t * m.s;
            var cy = m.sy + m.vy * m.t * m.s;
            drawLine(m.sx, m.sy, cx, cy, m.color);
            if (m.friendly) {
                ctx.fillStyle = 'red';
                ctx.fillRect(m.tx - 2, m.ty - 2, 4, 4);
            }
            if (collideCheck(m)) {
                explosions.push(makeExplosion(cx, cy, m.friendly));
                mis.splice(i--, 1);
            }
        }
    }

    function renderBuildings() {
        for (var i = 0; i < buildings.length; i++) {
            var b = buildings[i];
            ctx.fillStyle = 'blue';
            ctx.fillRect(b.x, canv.height - b.height, b.width, b.height * b.health);
            if (buildingCollide(b)) {
                buildings.splice(i--, 1);
            }
        }
    }

    function renderExplosions() {
        for (var i = 0; i < explosions.length; i++) {
            var exp = explosions[i];
            exp.t++;
            var r = getExplosionRadius(exp);
            if (r < 0) {
                explosions.splice(i--, 1);
                continue;
            }
            drawCircle(exp.x, exp.y, r, exp.color);
        }
    }

    function collideCheck(m) {
        var cx = m.sx + m.vx * m.t * m.s;
        var cy = m.sy + m.vy * m.t * m.s;
        var d = Math.sqrt(Math.pow(cx - m.tx, 2) + Math.pow(cy - m.ty, 2));
        if (cx < 0 || cx > canv.width || cy < 0 || cy > canv.height || d < 10) {
            return true;
        }
        if (!m.friendly) {
            for (var i = 0; i < explosions.length; i++) {
                var exp = explosions[i];
                d = Math.sqrt(Math.pow(cx - exp.x, 2) + Math.pow(cy - exp.y, 2));
                var r = getExplosionRadius(exp);
                if (d <= r) {
                    return true;
                }
            }

            for (var i = 0; i < buildings.length; i++) {
                var b = buildings[i];
                if (pointInBuilding(b, cx, cy)) {
                    return true;
                }
            }
        }
        return false;
    }

    function buildingCollide(b) {
        var l1x1 = b.x, l1y1 = canv.height - b.height;
        var l1x2 = b.x + b.width, l1y2 = canv.height - b.height;
        var l2x1 = b.x, l2y1 = canv.height - b.height;
        var l2x2 = b.x, l2y2 = canv.height;
        var l3x1 = b.x + b.width, l3y1 = canv.height - b.height;
        var l3x2 = b.x + b.width, l3y2 = canv.height;

        for (var i = 0; i < explosions.length; i++) {
            var exp = explosions[i];
            var r = getExplosionRadius(exp);
            if (
                lineInCircle(l1x1, l1y1, l1x2, l1y2, exp.x, exp.y, r) ||
                lineInCircle(l2x1, l2y1, l2x2, l2y2, exp.x, exp.y, r) ||
                lineInCircle(l3x1, l3y1, l3x2, l3y2, exp.x, exp.y, r)
            ) {
                return true
            }
        }
        return false;
    }

    function makeMissile(sx, sy, tx, ty, s, friendly) {
        var mag = Math.sqrt(Math.pow(sx - tx, 2) + Math.pow(sy - ty, 2));
        var vx = (tx - sx) / mag;
        var vy = (ty - sy) / mag;
        var color = friendly ? 'white' : 'yellow';
        return {
            sx: sx,
            sy: sy,
            tx: tx,
            ty: ty,
            vx: vx,
            vy: vy,
            friendly: friendly,
            color: color,
            children: [],
            s: s,
            t: 0
        };
    }

    function makeExplosion(x, y, friendly) {
        var color = friendly ? 'white' : 'yellow';
        return {
            x: x,
            y: y,
            t: 0,
            friendly: friendly,
            color: color
        };
    }

    function makeBuilding(pos) {
        var x = pos * canv.width;
        x += (rng() - 0.5) * (rng() * (canv.width / 6 - 20));
        if (x > canv.width) x -= (canv.width / 12);
        if (x < 0) x = 0;
        if (x > canv.width / 2 - 50 && x < canv.width / 2) x -= 50;
        if (x < canv.width / 2 + 50 && x >= canv.width / 2) x += 50;
        return {
            x: x,
            health: 1,
            width: rng() * canv.width / 40 + canv.width / 80,
            height: rng() * canv.height / 10 + canv.height / 40
        }
    }

    function getExplosionRadius(exp) {
        return (-Math.pow(exp.t/explodeDuration - 1, 4) + 1) * explodeRadius;
    }

    function pointInBuilding(b, x, y) {
        return x >= b.x && x <= b.x + b.width && y >= canv.height - b.height && y <= canv.height;
    }

    function lineInCircle(x1, y1, x2, y2, cx, cy, r) {
        x1 -= cx;
        x2 -= cx;
        y1 -= cy;
        y2 -= cy;
        var dx = x2 - x1;
        var dy = y2 - y1;
        var dr = Math.sqrt(dx*dx + dy*dy);
        var D = x1 * y2 - x2 * y1;

        var c = r * r * dr * dr - D * D;
        if (c >= 0) {
            var intr = Math.sqrt(r*r*dr*dr - D*D);
            var denom = dr*dr;
            cx1 = (D * dy + sgn(dy)*dx * intr) / denom;
            cx2 = (D * dy - sgn(dy)*dx * intr) / denom;
            cy1 = (-D * dx + Math.abs(dy) * intr) / denom;
            cy2 = (-D * dx - Math.abs(dy) * intr) / denom;

            return (cx1 >= x1 && cx1 <= x2 && cy1 >= y1 && cy1 <= y2) || (cx2 >= x1 && cx2 <= x2 && cy2 >= y1 && cy2 <= y2);
        }
        return false;
    }

    function sgn(x) {
        return x < 0 ? -1 : 1;
    }

    function drawLine(sx, sy, tx, ty, color) {
        ctx.beginPath();
        ctx.moveTo(sx, sy);
        ctx.lineTo(tx, ty);
        ctx.strokeStyle = color;
        ctx.stroke();
    }

    function drawCircle(x, y, r, color) {
        ctx.beginPath();
        ctx.arc(x, y, r, 0, Math.PI * 2);
        ctx.fillStyle = color;
        ctx.fill();
    }
    window.addEventListener('keydown', handleKey);
})(window, document);