/**
 * c-sections
 * by Raphael Rouvinov-Kats
 * 
 * Click and drag circles. See the points at which they intersect
 * */

var Circle = function(x, y, r) {
    this.x = x;
    this.y = y;
    this.r = r;
    this.selected = false;
    
    this.draw = function() {
        noFill();
        if(this.hoveredOver()) { fill(255, 163, 19, 60); }
        if(this.selected) { fill(0, 163, 19, 60); }
        ellipse(this.x, this.y, 2*r, 2*r);
    };
    
    // returns whether the mouse is over the circle
    this.hoveredOver = function() {
        return dist(pmouseX, pmouseY, this.x, this.y) <= r;
    };
    
    // if circle selected, moves it according to mouse movement
    this.move = function() {
        if(this.selected) {
            this.x += mouseX - pmouseX;
            this.y += mouseY - pmouseY;
        }
    };
    
    this.drawIntersectionPoints = function(other) {
        var x1 = this.x, x2 = other.x, 
            y1 = this.y, y2 = other.y, 
            r1 = this.r, r2 = other.r;
        var d = dist(x1, y1, x2, y2);
        var intersecting = true;
        
        /** determine if borders not intersecting **/
        if(r1 + r2 < d || d === 0 || // too far apart || same origin
           r1 > d + r2 || r2 > d + r1) { // this envelopes other || other envelopes this
            intersecting = false;
        }
        
        // http://math.stackexchange.com/questions/256100/how-can-i-find-the-points-at-which-two-circles-intersect
        if(intersecting) {
            //line(x1, y1, x2, y2); // for testing
            
            var l = (r1*r1 - r2*r2 + d*d)/(2*d);
            var h = sqrt(r1*r1-l*l);
            var dx = x2-x1;
            var dy = y2-y1;
            var px1 = l/d*dx+h/d*dy+x1;
            var px2 = l/d*dx-h/d*dy+x1;
            var py1 = l/d*dy-h/d*dx+y1;
            var py2 = l/d*dy+h/d*dx+y1;
            
            point(px1, py1);
            point(px2, py2);
        }
    };
};

// used in "objArray.forEach(applyDraw)"
var applyDraw = function(obj) {
    obj.draw();
};

var circles = [];

for(var i = 0; i < 10; i++) {
    circles.push(new Circle(random(0, 400), random(0, 400), random(10, 100)));
}

var draw = function() {
    background(255, 255, 255);
    
    // draw circles
    strokeWeight(1);
    circles.forEach(applyDraw);
    
    // draw intersection points
    strokeWeight(5);
    for(var i = 0; i < circles.length; i++) {
        for(var j = i+1; j < circles.length; j++) {
            circles[i].drawIntersectionPoints(circles[j]);
        }
    }
};

// if circle pressed, set it as selected
var mousePressed = function() {
    circles.forEach(function(cir){
        if(cir.hoveredOver()) { 
            cir.selected = true; 
        }
    });
};
var mouseClicked = mousePressed;

// if mouse is released, set all circles unselected
var mouseReleased = function() {
    circles.forEach(function(cir){
        cir.selected = false;
    });
};

// move selected circles when mouse is dragged
var mouseDragged = function() {
    circles.forEach(function(cir){
        cir.move();
    });
};