class ActiveSupport::Duration::ISO8601Serializer

def format_seconds(seconds)
  if @precision
    sprintf("%0.0#{@precision}f", seconds)
  else
    seconds.to_s
  end
end

def initialize(duration, precision: nil)
  @duration = duration
  @precision = precision
end

def normalize
  parts = @duration.parts.each_with_object(Hash.new(0)) do |(k, v), p|
    p[k] += v  unless v.zero?
  end
  # Convert weeks to days and remove weeks if mixed with date parts
  if week_mixed_with_date?(parts)
    parts[:days] += parts.delete(:weeks) * SECONDS_PER_WEEK / SECONDS_PER_DAY
  end
  parts
end

def serialize
  parts = normalize
  return "PT0S" if parts.empty?
  output = +"P"
  output << "#{parts[:years]}Y"   if parts.key?(:years)
  output << "#{parts[:months]}M"  if parts.key?(:months)
  output << "#{parts[:days]}D"    if parts.key?(:days)
  output << "#{parts[:weeks]}W"   if parts.key?(:weeks)
  time = +""
  time << "#{parts[:hours]}H"     if parts.key?(:hours)
  time << "#{parts[:minutes]}M"   if parts.key?(:minutes)
  if parts.key?(:seconds)
    time << "#{format_seconds(parts[:seconds])}S"
  end
  output << "T#{time}" unless time.empty?
  output
end

def week_mixed_with_date?(parts)
  parts.key?(:weeks) && parts.keys.intersect?(DATE_COMPONENTS)
end