#prepare the input which is a string containing new lines
def parse(input)
  data = []
  row = 0
  symbols = {}
  numbers = []
  input.each_line do |line|
    start_num = false
    num = ""
    num_cols = []

    line.chomp.chars.each_with_index do |c,col|
      if c == "."
        if start_num
          # finish a number
          numbers << [num.to_i, row, num_cols]
          start_num = false
          num = ""
          num_cols = []
        end
      elsif /\d/.match?(c)
        # a digit
        start_num = true
        num += c
        num_cols << col
      else
        # symbol
        if start_num
          # finish a number
          numbers << [num.to_i, row, num_cols]
          start_num = false
          num = ""
          num_cols = []
        end
        # fill adjacents
        symbols[row] = {} if symbols[row].nil?
        symbols[row][col-1] = true
        symbols[row][col+1] = true
        symbols[row-1] = {} if symbols[row-1].nil?
        symbols[row-1][col] = true
        symbols[row-1][col-1] = true
        symbols[row-1][col+1] = true
        symbols[row+1] = {}if symbols[row+1].nil?
        symbols[row+1][col] = true
        symbols[row+1][col-1] = true
        symbols[row+1][col+1] = true
      end
    end

    if start_num
      # finish a number
      numbers << [num.to_i, row, num_cols]
      start_num = false
      num = ""
      num_cols = []
    end
    row += 1
  end
  data = [symbols,numbers]
  data
end

# result should a single string or integer
def calculate(data)
  result = ""
  symbols, numbers = data
  selected_numbers = []
  numbers.each do |number_set|
    number, row, cols = number_set
    cols.each do |col|
      if symbols.dig(row,col)
        selected_numbers << number
        puts "selected: #{selected_numbers}"
        break
      end
    end
  end

  result = selected_numbers.reduce(&:+)

  result
end