Weekly Challenges - Minesweeper

minesweeper.rb

# A custom error class for handling invalid minesweeper boards
class ValueError < StandardError; end

# Minesweeper Board
class Board
  class << self
    def transform(board)
      raise ValueError, 'Invalid character' if invalid_char?(board)
      raise ValueError, 'Unequal row lengths' if uneven_lengths?(board)
      raise ValueError, 'Invalid border' if invalid_border?(board)

      board.map.with_index do |row, row_index|
        row[0] == '+' ? row : process_row(row, row_index, board)
      end
    end

    private

    def process_row(row, row_index, board)
      output = row.chars.map.with_index do |char, char_index|
        char == '|' ? char : process_char(row_index, char, char_index, board)
      end
      output.compact.join
    end

    def process_char(row_index, char, char_index, board)
      adjacent_spaces = adjacent(row_index, char_index)
      number_of_mines = mines(adjacent_spaces, board)
      char == '*' || number_of_mines.zero? ? char : number_of_mines
    end

    def adjacent(row_index, char_index)
      rows = row_index.zero? ? [0, 1] : (row_index - 1..row_index + 1).to_a
      chars = char_index.zero? ? [0, 1] : (char_index - 1..char_index + 1).to_a
      rows.product(chars).map do |combined|
        { row: combined[0], char: combined[1] }
      end
    end

    def mines(spaces, board)
      spaces.count { |space| board[space[:row]][space[:char]] == '*' }
    end

    def uneven_lengths?(board)
      board.any? { |row| row.size != board.first.size }
    end

    def invalid_border?(board)
      [board.first, board.last].any? { |border| border =~ /[^\+\-]/ }
    end

    def invalid_char?(board)
      board[1..-2].any? { |row| row =~ /[^\|\s\*]/ }
    end
  end
end