Spiral matrix

# title: Spiral matrix
# source: https://rosettacode.org/wiki/Spiral_matrix
# category: Rosetta Code
# difficulty: Medium
# summary: Fill a square matrix in clockwise spiral order.
# tags: popular, matrices, arrays, indexing
# vibe: 0.2

def blank_matrix(size)
  rows = []
  row = 0
  while row < size
    current = []
    column = 0
    while column < size
      current = current.push(0)
      column = column + 1
    end
    rows = rows.push(current)
    row = row + 1
  end
  rows
end

def set_cell(matrix, row, column, value)
  current = matrix[row]
  current[column] = value
  matrix[row] = current
  matrix
end

def spiral_matrix(size)
  matrix = blank_matrix(size)
  top = 0
  bottom = size - 1
  left = 0
  right = size - 1
  value = 1

  while top <= bottom && left <= right
    column = left
    while column <= right
      matrix = set_cell(matrix, top, column, value)
      value = value + 1
      column = column + 1
    end
    top = top + 1

    row = top
    while row <= bottom
      matrix = set_cell(matrix, row, right, value)
      value = value + 1
      row = row + 1
    end
    right = right - 1

    if top <= bottom
      column = right
      while column >= left
        matrix = set_cell(matrix, bottom, column, value)
        value = value + 1
        column = column - 1
      end
      bottom = bottom - 1
    end

    if left <= right
      row = bottom
      while row >= top
        matrix = set_cell(matrix, row, left, value)
        value = value + 1
        row = row - 1
      end
      left = left + 1
    end
  end

  matrix
end

def run
  spiral_matrix(5)
end