#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
      elsif c == "*"
        # 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,col]
      else
        # other symbol
        if start_num
          # finish a number
          numbers << [num.to_i, row, num_cols]
          start_num = false
          num = ""
          num_cols = []
        end
      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

def find_adjacent_numbers(row,col,numbers)
  adjacents = []
  matches = [
    [row-1,col-1],
    [row-1,col,],
    [row-1,col+1],
    [row,col-1],
    [row,col+1],
    [row+1,col-1],
    [row+1,col],
    [row+1,col+1]
  ]
  numbers.each do |number|
    num, row, cols = number
    cols.each do |col|
      if matches.include? [row,col]
        adjacents << num
        break
      end
    end

  end

  adjacents
end

# result should a single string or integer
def calculate(data)
  result = ""
  symbols, numbers = data
  selected_numbers = []
  symbols.each do |symbol|
    row,col = symbol
    adj = find_adjacent_numbers(row,col,numbers)
    if adj.length == 2
      selected_numbers << adj.first * adj.last
    end
  end

  result = selected_numbers.reduce(&:+)

  result
end