Spiral Matrix Sum

Problem Description

Given an m x n matrix of integers, write a function that traverses the matrix in spiral order (starting at the top-left corner and moving clockwise inward) and returns the sum of all visited elements.

Requirements

• The traversal starts at the top left of the matrix and continues in a spiral until all elements have been visited.
• The function should properly handle edge cases, such as empty matrices or matrices with only one row or one column.
• Assume that the matrix is always rectangular, meaning all rows have the same number of columns.

Example

For instance, given the following matrix:

[ [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9] ]

The spiral order traversal is: 1, 2, 3, 6, 9, 8, 7, 4, 5, and the function should return the sum which is 45.

Implement your solution in your preferred programming language.