/**
 * Ball bouncer
 * By Raphael Rouvinov-Kats
 * 
 * In this program I demonstrate rudimentary ball-to-line collision
 * detection and response
 * */

var Ball = function(x, y, dx, dy, radius) {
    this.pos = new PVector(x, y);
    this.vel = new PVector(dx, dy);
    this.radius = radius;
};

// thanks to chmike's answer to this StackOverflow question
// http://stackoverflow.com/questions/1073336/circle-line-collision-detection
Ball.prototype.collidesWith = function(lineObj) {
    // point A is the first position on the line
    // point B is the second position on the line
    // point C is the center of the circle
    // AB is the vector from A to B
    // AC is the vector from A to C
    var AB = lineObj.AB;
    var AC = new PVector();
        AC.add(lineObj.A);
        AC.sub(this.pos);
    
    // compute the triangle area times 2 (area = area2/2)
    var area2 = abs(AB.x*AC.y - AC.x*AB.y);
    //
    // compute the AB segment length
    var LAB = AB.mag();
    
    // compute the triangle height
    var h = area2/LAB;
    
    // if the line intersects the circle
    if( h < this.radius ) {
        // if the ray intersects the circle (not in the stackoverflow answer)
        if((this.pos.x > lineObj.A.x && this.pos.x < lineObj.B.x) ||
           (this.pos.y > min(lineObj.A.y, lineObj.B.y) && 
            this.pos.y < max(lineObj.A.y, lineObj.B.y))) {
            return true;
        }
    }
    
    // else
    return false;
};

// following a 'true' result from collision detection, this method is run to find
// what angle the ball will go following the collision
// thanks to Tommy's answer on this StackOverflow question
// http://stackoverflow.com/questions/4523434/calculate-angle-of-moving-ball-after-collision-with-angled-or-sloped-wall-that-i
Ball.prototype.calculateResultantAngle = function(lineObj) {
    // point A is the first position on the line
    // point B is the second position on the line
    // AB is the vector from A to B\
    var AB = lineObj.AB;
    
    // ABnormal is the normal to AB, normalized
    var ABnormal = new PVector();
        ABnormal.add(lineObj.ABnormal);
        ABnormal.normalize();
        
    var distanceAlongNormal = this.vel.dot(ABnormal);
    
    this.vel.x -= 2.0 * distanceAlongNormal * ABnormal.x;
    this.vel.y -= 2.0 * distanceAlongNormal * ABnormal.y;
};

Ball.prototype.move = function() {
    // switch x speed if past left or right canvas bounds
    if(this.pos.x >= width - this.radius || this.pos.x < this.radius) {
        this.pos.x = constrain(this.pos.x, 0, 400);
        this.vel.x = -this.vel.x;
    }
    
    // switchy speed if past top or bottom canvas bounds
    if(this.pos.y >= height - this.radius || this.pos.y < this.radius) {
        this.pos.y = constrain(this.pos.y, 0, 400);
        this.vel.y = -this.vel.y;
    }
    
    this.pos.add(this.vel);
};

Ball.prototype.draw = function() {
    var diameter = this.radius * 2;
    ellipse(this.pos.x, this.pos.y, diameter, diameter);
};

var Line = function(x1, y1, x2, y2) {
    if(x1 > x2) {
        var t = x1; x1 = x2; x2 = t;
            t = y1; y1 = y2; y2 = t;
    }
    
    // line points A (x1, y1) and B (x2, y2)
    this.A = new PVector(x1, x2);
    this.B = new PVector(x2, y2);
    
    var AB = new PVector();
        AB.add(this.A);
        AB.sub(this.B);
    
    // vector between points A and B
    this.AB = AB;
    
    // the normal of vector AB
    this.ABnormal = new PVector(-AB.y, AB.x);
};

Line.prototype.draw = function() {
    line(this.A.x, this.A.y, this.B.x, this.B.y);
};

var ballObj = new Ball(200, 100, 5, 5, 10);

var lines = [];
for(var i = 0; i < 10; i++) {
    lines.push(new Line(random(0,400), random(0,400), 
                        random(0,400), random(0,400)));
}

frameRate(0);
noStroke();
var draw = function() {
    // move the ball
    ballObj.move();
    
    // detect, calculate and respond to collision
    for(var i = 0; i < lines.length; i++) {
        var lineObj = lines[i];
        if(ballObj.collidesWith(lineObj)) {
            ballObj.calculateResultantAngle(lineObj);
        }
    }
    
    // draw the ball
    var noiseScale = 0.002;
    var n1 = noise(frameCount*noiseScale, 5*noiseScale)*10;
    var n2 = noise(frameCount*noiseScale, 50*noiseScale)*205;
    var n3 = noise(frameCount*noiseScale, 500*noiseScale)*205;
    fill(n1+50, n2+50, n3+50);
    ballObj.draw();
};