View.Set ("position:centre;centre,graphics:300;300,title:Bouncing Balls,nobuttonbar")
var totalballs : int := 15 %NOTE : to increase how many balls will spawn this number must be at least equal to the max number of balls
var x, y, dx, dy : array 1 .. totalballs of int
var dx_temp, dy_temp : array 1 .. totalballs of real
var movedist1, movedist2, collangle, mass, a1, a2, nX, nY, optimisedP : real

var px, py : int
px := maxx div 2
py := maxy div 2
var keys : array char of boolean
var hit : boolean := false
var respawn : boolean := true
var respawnx, respawny : int
var lives : int := 3
const ballradius := 8
const ballcollidedistance := ballradius * 2
var timer : int
setscreen ("offscreenonly")
mass := 1

for i : 1 .. totalballs
    x (i) := Rand.Int (20 + ballradius, maxx - 20 - ballradius)
    y (i) := Rand.Int (20 + ballradius, maxy - 20 - ballradius)
    dx (i) := Rand.Int (-3, 3)
    dy (i) := Rand.Int (-3, 3)
end for

proc drawscreen
    for i : 1 .. maxx by 20
        Draw.FillStar (i, 0, i + 20, 20, 2)
        Draw.FillStar (i, maxy - 20, i + 20, maxy, 2)
    end for
    for k : 20 .. maxy - 20 by 20
        Draw.FillStar (0, k, 20, k + 20, 2)
        Draw.FillStar (maxx - 20, k, maxx, k + 20, 2)
    end for
    locate (3, 3)
end drawscreen

proc ball_movement
    for i : 1 .. totalballs
        %wall bouncing
        if x (i) > maxx - 20 - ballradius then
            dx (i) := -dx (i)
            x (i) += dx (i)
        end if
        if x (i) < 20 + ballradius then
            dx (i) := -dx (i)
            x (i) += dx (i)
        end if
        if y (i) > maxy - 20 - ballradius then
            dy (i) := -dy (i)
            y (i) += dy (i)
        end if
        if y (i) < 20 + ballradius then
            dy (i) := -dy (i)
            y (i) += dy (i)
        end if

        x (i) += dx (i)
        y (i) += dy (i)
        drawfilloval (x (i), y (i), ballradius, ballradius, blue)
    end for
end ball_movement

proc balls_collide
    for i : 1 .. totalballs
        for k : i .. totalballs

            if k not= i then
                if Math.Distance (x (i), y (i), x (k), y (k)) < ballcollidedistance then
         %CREDIT :  THOUGHTFUL
                    if y (k) - y (i) not= 0 and x (k) - x (i) not= 0 then
                        collangle := arctand ((y (k) - y (i)) / ((x (k) - x (i))))

                        nX := cosd (collangle)
                        nY := sind (collangle)

                        a1 := x (i) * nX + y (i) * nY
                        a2 := x (k) * nX + y (k) * nY

                        optimisedP := (2.0 * (a1 - a2)) / (mass + mass)

                        x (i) := x (i) - (round (optimisedP) * round (mass) * round (nX))
                        y (i) := y (i) - (round (optimisedP) * round (mass) * round (nY))
                        x (k) := x (k) + (round (optimisedP) * round (mass) * round (nX))
                        y (k) := y (k) + (round (optimisedP) * round (mass) * round (nY))
                        % moves the balls forward a step so they dont get stuck with each other( but the balls will still stick)
                        x (i) += dx (i)
                        y (i) += dy (i)
                        x (k) += dx (k)
                        y (k) += dy (k)
                    end if
                end if
            end if
        end for
    end for
end balls_collide

proc player_control
    Input.KeyDown (keys)
    if keys (KEY_UP_ARROW) then
        py += 2
    end if
    if keys (KEY_DOWN_ARROW) then
        py -= 2
    end if
    if keys (KEY_RIGHT_ARROW) then
        px += 2
    end if
    if keys (KEY_LEFT_ARROW) then
        px -= 2
    end if
    drawfilloval (px, py, ballradius, ballradius, brightred)
end player_control

proc player_boundaries
    if px > maxx - 50 - ballradius then
        px := maxx - 50 - ballradius
    end if
    if px < 50 + ballradius then
        px := 50 + ballradius
    end if
    if py > maxy - 50 - ballradius then
        py := maxy - 50 - ballradius
    end if
    if py < 50 + ballradius then
        py := 50 + ballradius
    end if
end player_boundaries

proc relocate
    lives -= 1
    delay (1000)
    px := 20 + ballradius
    py := 20 + ballradius
end relocate


loop
    timer := Time.Elapsed
    totalballs := round (timer / 5000)
    exit when totalballs > 20 or hit = true
    cls
    drawscreen

    player_control
    player_boundaries

    ball_movement
    balls_collide
    for k : 1 .. totalballs
        if Math.Distance (px, py, x (k), y (k)) < ballcollidedistance then
            hit := true
        end if
    end for
    View.Update
    delay (10)
end loop

delay (500)
cls
locate (7, 5)

put "Thanks for playing,\n       -Cervantes"