module Xlsxrb::Ooxml::Utils

# File lib/xlsxrb/ooxml/utils.rb, line 57
def date_to_serial(date)
  serial = (date - EPOCH_1900).to_i
  # Lotus 1-2-3 bug: serial 60 = Feb 29, 1900 (doesn't exist).
  # Dates on or after Mar 1, 1900 (raw serial >= 60) need +1.
  serial += 1 if serial >= 60
  serial
end

# File lib/xlsxrb/ooxml/utils.rb, line 73
def datetime_to_serial(time)
  date = time.to_date
  day_serial = date_to_serial(date)
  # Fractional part: seconds since midnight / seconds per day
  seconds_since_midnight = (time.hour * 3600) + (time.min * 60) + time.sec
  day_serial + (seconds_since_midnight.to_f / 86_400)
end

# File lib/xlsxrb/ooxml/utils.rb, line 96
def hash_password(password, algorithm: "SHA-512", salt: nil, spin_count: 100_000)
  raise ArgumentError, "password must be a String" unless password.is_a?(String)
  raise ArgumentError, "spin_count must be a positive Integer" unless spin_count.is_a?(Integer) && spin_count.positive?

  salt_bytes = (salt || SecureRandom.random_bytes(16)).b
  # OOXML sheet/workbook protection hashing uses UTF-16LE password bytes.
  password_bytes = password.encode("UTF-16LE").b

  digest_name = algorithm.tr("-", "")
  hash = OpenSSL::Digest.digest(digest_name, salt_bytes + password_bytes)

  spin_count.times do |i|
    iteration_bytes = [i].pack("V") # little-endian uint32
    hash = OpenSSL::Digest.digest(digest_name, hash + iteration_bytes)
  end

  {
    algorithm_name: algorithm,
    hash_value: [hash].pack("m0"),
    salt_value: [salt_bytes].pack("m0"),
    spin_count: spin_count
  }
end

# File lib/xlsxrb/ooxml/utils.rb, line 66
def serial_to_date(serial)
  # Adjust for Lotus 1-2-3 bug.
  serial -= 1 if serial > 60
  EPOCH_1900 + serial
end

# File lib/xlsxrb/ooxml/utils.rb, line 82
def serial_to_datetime(serial)
  int_part = serial.to_i
  frac = serial - int_part
  date = serial_to_date(int_part)
  total_seconds = (frac * 86_400).round
  hours = total_seconds / 3600
  minutes = (total_seconds % 3600) / 60
  seconds = total_seconds % 60
  Time.utc(date.year, date.month, date.day, hours, minutes, seconds)
end