quien me puede explicar este codigo de como es la funcion

var unit = 15;
var uwh = 20;
var canMove = false;
var dir = 2;
var score = 0;
aPieceList = new Array();
mouseListener = new Object();
mouseListener.onMouseDown = function()
{
if (!canMove)
{
canMove = true;
startGame();
}
};
Mouse.addListener(mouseListener);
k = new Object();
k.onKeyDown = function()
{
var k = Key.getCode();
if (k == Key.UP && dir != 2 && canMove)
{
dir = 0;
canMove = false;
}
else if (k == Key.LEFT && dir != 3 && canMove)
{
dir = 1;
canMove = false;
}
else if (k == Key.DOWN && dir != 0 && canMove)
{
dir = 2;
canMove = false;
}
else if (k == Key.RIGHT && dir != 1 && canMove)
{
dir = 3;
canMove = false;
}
};
Key.addListener(k);
function addPiece()
{
var p = this.attachMovie("piece", "piece" + aPieceList.length, aPieceList.length);
p._x = aPieceList[aPieceList.length - 1]._x;
p._y = aPieceList[aPieceList.length - 1]._y;
aPieceList.push(p);
}
function moveFood()
{
var moveIt = true;
while (moveIt)
{
food._x = Math.floor(Math.random() * uwh) * unit;
food._y = Math.floor(Math.random() * uwh) * unit;
moveIt = false;
for (var i = 0; i < aPieceList.length; i++)
{
if (aPieceList[i]._x == food._x && aPieceList[i]._y == food._y)
{
moveIt = true;
}
}
}
}
function gameOver()
{
delete this.onEnterFrame;
tScore.text = "You Lose. Score: " + score;
canMove = false;
}
function startGame()
{
for (var i = aPieceList.length - 1; i >= 0; i--)
{
aPieceList[i].removeMovieClip();
aPieceList.pop();
}
score = 0;
var p = this.attachMovie("piece", "piece" + aPieceList.length, aPieceList.length);
aPieceList.push(p);
p._x = 10 * unit;
p._y = 10 * unit;
var food = this.attachMovie("food", "food", -1);
var c = 0;
moveFood();
var startingLength = 3;
for (var i = 1; i < startingLength; i++)
{
addPiece();
}
this.onEnterFrame = function()
{
canMove = true;
tScore.text = score;
for (var i = aPieceList.length - 1; i > 0; i--)
{
aPieceList[i]._x = aPieceList[i - 1]._x;
aPieceList[i]._y = aPieceList[i - 1]._y;
}
if (dir == 0)
{
aPieceList[0]._y -= unit;
}
else if (dir == 1)
{
aPieceList[0]._x -= unit;
}
else if (dir == 2)
{
aPieceList[0]._y += unit;
}
else if (dir == 3)
{
aPieceList[0]._x += unit;
}
if (aPieceList[0]._y / unit == 20)
{
aPieceList[0]._y = 0;
}
else if (aPieceList[0]._y / unit == -1)
{
aPieceList[0]._y = 19 * unit;
}
else if (aPieceList[0]._x / unit == -1)
{
aPieceList[0]._x = 19 * unit;
}
else if (aPieceList[0]._x / unit == 20)
{
aPieceList[0]._x = 0;
}
if (aPieceList[0]._x == food._x && aPieceList[0]._y == food._y)
{
score += 10 * aPieceList.length / 2;
moveFood();
addPiece();
}
for (var i = 1; i < aPieceList.length; i++)
{
if (aPieceList[0]._x == aPieceList[i]._x && aPieceList[0]._y == aPieceList[i]._y)
{
gameOver();
}
}
};
}