//---- normal P5 code -------------------------------------------------------

var data = [];

//slope
var m = 1;

//y-intercept
var b = 0;

function setup()       
{
    createCanvas(400, 400);
    background(51);
}

function mousePressed(){
    var x = map(mouseX, 0, width, 0, 1);
    var y = map(mouseY, 0, width, 1, 0);
    
    var  point = createVector(x, y);
    data.push(point);
}

function drawLine(){
    var x1 = 0;
    var y1 = m * x1 + b;
    
    var x2 = 1;
    var y2 = m * x2 + b;
    
    x1 = map(x1, 0, 1, 0, width)
    y1 = map(y1, 0, 1, height, 0)
    
    x2 = map(x2, 0, 1, 0, width)
    y2 = map(y2, 0, 1, height, 0)
    
    
    stroke (255, 0, 255);
    line(x1, y1, x2, y2);
}

function linearRegression(){
    
   var xsum = 0;
   var ysum = 0;
    
    for (var i = 0; i < data.length; i++){
        
        xsum += data[i].x;
        ysum += data[i].y;
    } 
    
    var xmean = xsum / data.length;
    var ymean = ysum / data.length;
    
    var num = 0;
    var den = 0;
    
    for (var i = 0; i < data.length; i++){
        
        var x = data[i].x;
        var y = data[i].y;
        num += (x - xmean) * (y - ymean);
        den += (x - xmean) * (x - xmean);     
    }
    
    m = num / den;
    b = ymean - (m * xmean);
    
}

function draw()             
{
    background(51);
    
    for(var i = 0; i < data.length; i++){
        var x = map(data[i].x, 0, 1, 0, width);
        var y = map(data[i].y, 0, 1, height, 0);
        
        fill(255);
        stroke(255);
        ellipse(x,y,8,8);
    }
    if (data.length > 1){
        linearRegression();
        drawLine();
    }
    
}