class ReeNumber::NumberToHuman

def calculate_exponent(number, locale, units)
  exponent = number != 0 ? Math.log10(number.abs).floor : 0
  unit_exponents(units, locale).find { |e| exponent >= e } || 0
end

def call(number, **opts)
  options = DEFAULTS.merge(opts)
  number = round_helper(
    number,
    **slice(options, [:precision, :significant, :round_mode])
  )
  number = Float(number)
  exponent = calculate_exponent(
    number, options[:locale], options[:units]
  )
  number = number / (10**exponent)
  rounded_number = number_to_rounded(
    number,
    **slice(
      options,
      [:precision, :significant, :strip_insignificant_zeros, :round_mode]
    )
  )
  unit = determine_unit(
    exponent, options[:units], options[:locale]
  )
  result_number = options[:format]
    .gsub("%n", rounded_number)
    .gsub("%u", unit)
    .strip
  number_to_delimited(
    result_number,
    **slice(options, [:separator, :delimiter])
  )
end

def determine_unit(exponent, units, locale)
  exp = DECIMAL_UNITS[exponent]
  case units
  when Hash
    units[exp] || ""
  when String, Symbol
    t("human.#{units}.#{exp}", locale: locale, default_by_locale: :en)
  else
    t("human.decimal_units.#{exp}", count: number.to_i, default_by_locale: :en)
  end
end

def unit_exponents(units, locale)
  case units
  when Hash
    units
  when String, Symbol
    t("human.#{units}", locale: locale, raise: true, default_by_locale: :en)
  else
    raise ArgumentError, ":units must be a Hash or String translation scope."
  end.keys.map { |e_name| INVERTED_DECIMAL_UNITS[e_name] }.sort_by(&:-@)
end