class Tins::Duration

def self.parse(string, template: '%S%d+%h:%m:%s.%f')
  s, t = string.to_s.dup, template.dup
  d, sd = 0, 1
  loop do
    t.sub!(/\A(%[Sdhmsf%]|.)/) { |directive|
      case directive
      when '%S' then s.sub!(/\A-?/)   { sd *= -1 if _1 == ?-; '' }
      when '%d' then s.sub!(/\A\d+/)  { d += 86_400 * _1.to_i; '' }
      when '%h' then s.sub!(/\A\d+/)  { d += 3_600 * _1.to_i; '' }
      when '%m' then s.sub!(/\A\d+/)  { d += 60 * _1.to_i; '' }
      when '%s' then s.sub!(/\A\d+/)  { d += _1.to_i; '' }
      when '%f' then s.sub!(/\A\d+/)  { d += Float(?. + _1); '' }
      when '%%' then
        if s[0] == ?%
          s[0] = ''
        else
          raise "expected %s, got #{s.inspect}"
        end
      else
        if directive == s[0]
          s[0] = ''
        else
          raise ArgumentError, "expected #{t.inspect}, got #{s.inspect}"
        end
      end
      ''
    } or break
  end
  sd * d
end

def <=>(other)
  to_f <=> other.to_f
end

def days?
  @days > 0
end

def format(template = '%S%d+%h:%m:%s.%f', precision: nil)
  result = template.gsub(/%[DdhmSs]/) { |directive|
    case directive
    when '%S' then ?- if negative?
    when '%d' then @days
    when '%h' then '%02u' % @hours
    when '%m' then '%02u' % @minutes
    when '%s' then '%02u' % @seconds
    when '%D' then format_smart
    end
  }
  if result.include?('%f')
    if precision
      fractional_seconds = "%.#{precision}f" % @fractional_seconds
    else
      fractional_seconds = '%f' % @fractional_seconds
    end
    result.gsub!('%f', fractional_seconds[2..-1])
  end
  result
end

def format_smart
  template  = '%h:%m:%s'
  precision = nil
  if days?
    template.prepend '%d+'
  end
  if fractional_seconds?
    template << '.%f'
    precision = 3
  end
  template.prepend '%S'
  format template, precision: precision
end

def fractional_seconds?
  @fractional_seconds > 0
end

def hours?
  @hours > 0
end

def initialize(seconds)
  @negative = seconds < 0
  seconds = seconds.abs
  @original_seconds = seconds
  @days, @hours, @minutes, @seconds, @fractional_seconds =
    [ 86_400, 3600, 60, 1, 0 ].inject([ [], seconds ]) {|(r, s), d|
      if d > 0
        dd, rest = s.divmod(d)
        r << dd
        [ r, rest ]
      else
        r << s
      end
    }
end

def minutes?
  @minutes > 0
end

def negative?
  @negative
end

def seconds?
  @seconds > 0
end

def to_f
  @original_seconds.to_f
end

def to_s
  format_smart
end