Verify EAN and fix if available.

ean.coffee

class EAN
  valid_code: (ean) ->
    return false if ean.match(/[^0-9]/)
    ean += '00000' if ean.length == 8
    return false unless ean.length == 13
    return ean if is_valid(ean)
    [ean[1], ean[0]] = [ean[0], ean[1]]
    return ean if is_valid(ean)
    false

  is_valid: (ean) ->
    [ean_digits, check_digit] = split_value_and_checkdigit(ean)
    even = numberize(ean_digits, [1,3,5,7,9,11])
    odd = numberize(ean_digits, [0,2,4,6,8,10])
    total = even * 3 + odd
    calc_checksum(total) == check_digit

  split_value_and_checkdigit: (value) ->
    check_digit = value.substring(value.length-1)
    origin_digits = value.substring(0, value.length-1)
    [origin_digits, check_digit]

  numberize: (digits, array) ->
    results = Number(digits[index]) for index in array
    results.reduce (x, y) -> x + y

  calc_checksum: (total) ->
    s = total % 10
    s = 10 - s if s != 0
    s

window.EAN = EAN