xna - How do I ensure that my 2D side-scroller camera stays within the world bounds?

I have tried implementing a basic 2D sidescroller camera in XNA, but I don't want it to be able to scroll past the edges of my tile map!

I tried to fix it, but when I get the left side working, the right stops working...

How do I do this right?

EDIT: After Anko

public Matrix transform;    
Viewport view; 
Vector2 center; 

public void Update(GameTime gameTime, Player player) {
    center = new Vector2(player.Position.X + (player.Bounds.Width / 2) - (960 / 2), 0);

    float cameraX = center.X;
    float cameraWidth = view.Width;


    float worldWidth = 1760;

    if (cameraX < 0) 
        cameraX = 0;
    else if  ( cameraX + cameraWidth > worldWidth)
        cameraX = worldWidth - cameraWidth;

    transform = Matrix.CreateTranslation(new Vector3(-cameraX, 0, 0)); 

Answer

Let's draw it! _{(Again ;3)}

Imagine all the grassy and skyey bits are your game world. That lighter coloured rectangle framed in red is the region the camera is looking at. A player would only actually see what's in the camera. We want the camera to always stay in the game world.

(x,y) is the camera position
w and h are the camera's width and height

Let's also say your game world has width world_w and height world_h.

To take care of left, we want to ensure x > 0
To take care of right, we want to ensure x + w < world_w

To take care of the top, we want to ensure y > 0
To take care of bottom, we want to ensure y + h < world_h

So, before you apply a transformation matrix to translate by x, y, check that our assumptions indeed are true, and if not, correct them so they just about are:

if x < 0 then
    x = 0
elseif x + w > world_w
    x = world_w - w

if y < 0 then
    y = 0
elseif y + h > world_h
    y = world_h - h

No more escaping camera!

Note that you might want to build in a special case to detect if your world is smaller than your camera, if such a tiny world might happen in your game.