UPC

# title: UPC
# source: https://rosettacode.org/wiki/UPC
# category: Rosetta Code
# difficulty: Intro
# summary: Validate sample UPC codes with the standard checksum rule.
# tags: popular, strings, validation, checksum
# vibe: 0.2

def digit_value(char)
  "0123456789".index(char)
end

def valid_upc?(code)
  sum = 0
  index = 0

  while index < code.length
    digit = digit_value(code.slice(index))
    if index.even?
      sum = sum + (digit * 3)
    else
      sum = sum + digit
    end
    index = index + 1
  end

  sum % 10 == 0
end

def run
  [
    { code: "036000291452", valid: valid_upc?("036000291452") },
    { code: "042100005264", valid: valid_upc?("042100005264") },
    { code: "123456789999", valid: valid_upc?("123456789999") }
  ]
end