Smith numbers

# title: Smith numbers
# source: https://rosettacode.org/wiki/Smith_numbers
# category: Rosetta Code
# difficulty: Medium
# summary: Detect Smith numbers by comparing the digit sum of a composite integer with the digit sum of its prime factors.
# tags: popular, math, primes, factorization
# vibe: 0.2

def digit_sum(value)
  total = 0
  current = value.abs

  while current > 0
    total = total + (current % 10)
    current = current / 10
  end

  total
end

def prime?(number)
  if number < 2
    return false
  end

  candidate = 2
  while candidate * candidate <= number
    if number % candidate == 0
      return false
    end
    candidate = candidate + 1
  end

  true
end

def factor_digit_sum(number)
  total = 0
  remaining = number
  factor = 2

  while factor * factor <= remaining
    while remaining % factor == 0
      total = total + digit_sum(factor)
      remaining = remaining / factor
    end
    factor = factor + 1
  end

  if remaining > 1
    total = total + digit_sum(remaining)
  end

  total
end

def smith?(number)
  if prime?(number)
    return false
  end

  digit_sum(number) == factor_digit_sum(number)
end

def run
  [
    { value: 4, smith: smith?(4) },
    { value: 22, smith: smith?(22) },
    { value: 27, smith: smith?(27) },
    { value: 58, smith: smith?(58) },
    { value: 85, smith: smith?(85) },
    { value: 13, smith: smith?(13) }
  ]
end