>>> import datetime
>>> from timelines import timespan, timelayer

A timespan object has a start time and an end time. It can be created either by specifying a start time and an elapsed time, or by specifying both start and end times:

>>> span1 = timespan(datetime.datetime(1984, 11, 26), datetime.timedelta(1))
>>> span2 = timespan(datetime.datetime(1984, 11, 26) + datetime.timedelta(2), datetime.datetime(1984, 11, 26) + datetime.timedelta(2, 50))
>>> span1.start
datetime.datetime(1984, 11, 26, 0, 0)
>>> span1.elapsed
datetime.timedelta(1)

The elapsed time of a timespan is the timedelta between its start and end times:

>>> span1.elapsed == span1.end - span1.start
True

A timelayer object is a sorted bag of non-overlapping timespans which know the order in which they occur:

>>> layer = timelayer(span2, span1)
>>> list(layer) == [span1, span2]
True

Just like a timespan, a timelayer knows its own start and end times:

>>> layer.start == span1.start
True
>>> layer.end == span2.end
True

The elapsed duration of a timelayer is the sum of the elapsed durations of the timespans it contains, NOT the delta between its start and end times:

>>> layer.elapsed == span1.elapsed + span2.elapsed
True
>>> layer.elapsed == layer.end - layer.start
False

You can add new timespans to a timelayer:

>>> layer.start
datetime.datetime(1984, 11, 26, 0, 0)
>>> layer.end
datetime.datetime(1984, 11, 28, 0, 0, 50)

>>> layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(1), datetime.timedelta(0, 600)))
>>> layer.start
datetime.datetime(1984, 11, 25, 0, 0)
>>> layer.end
datetime.datetime(1984, 11, 28, 0, 0, 50)

However, you cannot add new timespans which overlap any existing timespans:

>>> layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(2), datetime.timedelta(2)))
Traceback (most recent call last):
...
RuntimeError: <timelayer datetime.datetime(1984, 11, 24, 0, 0) => datetime.datetime(1984, 11, 26, 0, 0) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 25, 0, 0) => datetime.datetime(1984, 11, 25, 0, 10)>

>>> layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(1) + datetime.timedelta(0, 300), datetime.timedelta(0, 600)))
Traceback (most recent call last):
...
RuntimeError: <timelayer datetime.datetime(1984, 11, 25, 0, 5) => datetime.datetime(1984, 11, 25, 0, 15) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 25, 0, 0) => datetime.datetime(1984, 11, 25, 0, 10)>

>>> layer.add(timespan(datetime.datetime(1984, 11, 26) + datetime.timedelta(0, 300), datetime.timedelta(0, 1200)))
Traceback (most recent call last):
...
RuntimeError: <timelayer datetime.datetime(1984, 11, 26, 0, 5) => datetime.datetime(1984, 11, 26, 0, 25) (contains 1 timespans)> overlaps <timespan datetime.datetime(1984, 11, 26, 0, 0) => datetime.datetime(1984, 11, 27, 0, 0)>

You can also add constraints to a timelayer. Constraints allow you to freeze the start time and/or end time of a timelayer, or to put an upper bound on the total elapsed time of a layer. New timespans cannot be added to a layer if they fail its constraints:

>>> layer.freeze_start()
>>> layer.add(timespan(datetime.datetime(1984, 11, 26) - datetime.timedelta(4), datetime.timedelta(2)))
Traceback (most recent call last):
...
RuntimeError: datetime.datetime(1984, 11, 22, 0, 0) is earlier than frozen start datetime.datetime(1984, 11, 25, 0, 0)

>>> layer.freeze_elapsed(datetime.timedelta(3))
>>> layer.add(timespan(datetime.datetime(1985, 11, 26), datetime.datetime(1985, 11, 29)))
Traceback (most recent call last):
...
RuntimeError: Total elapsed time datetime.timedelta(4, 650) is greater than frozen allowed elapsed time datetime.timedelta(3)

>>> layer.freeze_end(datetime.datetime(1985, 11, 27))
>>> layer.add(timespan(datetime.datetime(1985, 11, 26, 23), datetime.datetime(1985, 11, 27, 1)))
Traceback (most recent call last):
...
RuntimeError: datetime.datetime(1985, 11, 27, 1, 0) is later than frozen end datetime.datetime(1985, 11, 27, 0, 0)