function Grid(size, changeCallback)
{
  var grid = new Array(size);
  
  var data = {
    grid: grid,
    size: size
  };
  
  this.get = function(row, col)
  {
    if (isOutOfBounds(data, row, col))
      throw new RangeError("Row or Column value out of bounds");
    return grid[row] && grid[row][col];
  }
  this.set = function(row, col, value)
  {
    if (isOutOfBounds(data, row, col))
      throw new RangeError("Row or Column value out of bounds");
      
    if (!grid[row])
      grid[row] = new Array(size);
    var before = grid[row][col];
    grid[row][col] = value;
    
    if (typeof changeCallback === "function")
      changeCallback(row, col, before, value);
    
    return before;
  }
  
  this.isOutOfBounds = isOutOfBounds.bind(this, data);
  
  Object.defineProperty(this, "size", {
    get: function() {return size; },
    enumerable: true
  });
  
}

function isOutOfBounds(data, row, col)
{
  return row < 0 || row >= data.size || col < 0 || col >= data.size;
}

module.exports = Grid;