// click to add new lines!

var bgColor = color(255, 247, 247);
var lineColor = color(255, 0, 0);
var intersectColor = color(125, 87, 201, 150);
var intersectDiam = 10;
var randomLineCount = 10;
var e = 0.1; // epsilon - ensures that vertices get counted as intersections

var Line = function(x1, y1, x2, y2) {
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
    
    this.gX1 = function() { return x1; };
    this.gX2 = function() { return x2; };
    this.gY1 = function() { return y1; };
    this.gY2 = function() { return y2; };
    this.sX1 = function(val) { x1 = val; };
    this.sX2 = function(val) { x2 = val; };
    this.sY1 = function(val) { y1 = val; };
    this.sY2 = function(val) { y2 = val; };

    // determine if point is in line 'bounds'
    // simply makes sure the point isn't out of the outer x or y of the line
    this.pointInBounds = function(px, py) {
        if(((px < x1-e && px < x2-e) || (px > x1+e && px > x2+e)) && // line1x
           ((py < y1-e && py < y2-e) || (py > y1+e && py > y2+e))){ // line1y
            return false;
        }
        return true;
    };
    
    // line equations
    // y - l1[1] = (l1[1]-l1[3])/(l1[0]-l1[2])*(x-l1[0]) first line eq
    // y - l2[1] = (l2[1]-l2[3])/(l2[0]-l2[2])*(x-l2[0]) second line eq
    //
    // x1 = l1[0], y1 = l1[1], x2 = l2[0], y2 = l2[1]
    // (lN[1]-lN[3])/(lN[0]-lN[2]) = mN
    // y - y1 = m1*(x-x1) first line eq
    // y - y2 = m2*(x-x2) second line eq
    //
    // intersection
    // y1 + m1*(x-x1) = y2 + m2*(x-x2)
    // y1 + m1*x-m1*x1 = y2 + m2*x-m2*x2
    // x(m1-m2) = y2 - y1 + m1*x1 - m2*x2
    // x = (y2 - y1 + m1*x1 - m2*x2)/(m1-m2)
    // y = y1 + m1*(intX-x1)
    this.getIntersectionWith = function(l) {
        var x3 = l.gX1(), y3 = l.gY1(); // second line first coordinate
        
        var m1 = (y1-y2)/(x1-x2); // first line slope
        var m2 = (y3-l.gY2())/(x3-l.gX2()); // second line slope
        
        // parallels
        if(m1 === m2) {
            println("parallel line detected. you live life on the edge.");
            return [null, null];
        }
        
        var intX = (y3 - y1 + m1*x1 - m2*x3)/(m1-m2);
        var intY = y1 + m1*(intX-x1);
        
        return [intX, intY];
    };
};

var lines = [];

// line that moves
var dynamicLine = new Line(320, 120, 140, 310);

lines.push(dynamicLine);

// add a bunch of randome lines
for(var i = 0; i < randomLineCount; i++) {
    lines.push(new Line(lines[lines.length-1].gX2(), lines[lines.length-1].gY2(), 
                        random(0, 400), random(0, 400)));
}

var newLineCoords = [lines[lines.length-1].gX2(), lines[lines.length-1].gY2()];

var draw = function() {
    noStroke();
    fill(bgColor);
    rect(0, 0, 400, 400);
    if(newLineCoords.length === 0) {
        dynamicLine.sX1(pmouseX);
        dynamicLine.sY1(pmouseY);
    } else {
        dynamicLine.sX1(newLineCoords[0]);
        dynamicLine.sY1(newLineCoords[1]);
    }
    dynamicLine.sX2(mouseX);
    dynamicLine.sY2(mouseY);
    
    for(var i = 0; i < lines.length; i++) {
        var l = lines[i];
        
        // draw line
        stroke(lineColor);
        line(l.gX1(), l.gY1(), l.gX2(), l.gY2());
        
        // find and draw intersections
        for(var j = i + 1; j < lines.length; j++) {
            var lj = lines[j];
            
            // calculate intersection
            var intrsect = l.getIntersectionWith(lj);
            var intX = intrsect[0];
            var intY = intrsect[1];
            
            var intersectInBound = false;
            if(intX === null || intY === null) {
                intersectInBound = false;
            } else {
                intersectInBound = (l.pointInBounds(intX, intY) &&
                                    lj.pointInBounds(intX, intY));
            }
            
            // draw intersection
            if(intersectInBound) {
                noStroke();
                fill(intersectColor);
                ellipse(intX, intY, intersectDiam, intersectDiam);
            }
        }
    }
};

var mouseClicked = function() {
    if(newLineCoords.length === 0) {
        newLineCoords[0] = mouseX;
        newLineCoords[1] = mouseY;
    } else {
        lines.push(new Line(newLineCoords[0], newLineCoords[1],
                            mouseX, mouseY));
        newLineCoords = [lines[lines.length-1].gX2(), lines[lines.length-1].gY2()];
    }
};