update method

void update({ DateTime? begin, DateTime? end, Duration? duration, })

The update function handles not only the updates to an existing Timespan but also acts as a quasi constructor. Since all parameters are optional the default behaviour is explained in the update-function itself.

Implementation

void update({DateTime? begin, DateTime? end, Duration? duration}) {
  if (duration == null) {
    /// use the supplied begin or unix time = 0
    this.begin = begin ?? DateTime(1970);

    /// use the supplied end or now
    this.end = end ?? DateTime.now();

    /// calc resulting duration
    this.duration = this.end.difference(this.begin);
  } else if (begin != null && end != null) {
    /// If this condition is reached, all arguments are given.
    /// Hence the duration needs to match the begin and end times.
    if (begin.difference(end).compareTo(duration) == 0) {
      this.begin = begin;
      this.end = end;
      this.duration = duration;
    } else {
      throw ArgumentError("Starttime endtime and duration do not match");
    }

    /// if only begin and duration are given,
    /// calc the end time from begin + duration
  } else if (begin != null) {
    this.begin = begin;
    this.end = begin.add(duration);
    this.duration = duration;

    /// if only end and duration are given,
    /// calc the begin time from end - duration
  } else {
    this.end = end ?? DateTime.now();
    this.begin = this.end.subtract(duration);
    this.duration = duration;
  }
}