Unify timetable snapshot handling for GTFS-RT and Siri

[leonardehrenfried]

Summary

We discussed in one of the realtime meetings that the GTFS-RT and Siri code needs to be unified. This PR makes one step into that direction by introducing an abstract base class for handling the timetable snaphots. This is then used by both the Siri and GTFS-RT updaters.

Previously their handling of the snapshot was very similar, but not identical: Siri would always initialise a snapshot in the constructor but GTFS-RT would not. This meant that I had to modify the tests ever so slightly to make them pass, reflecting the fact that GTFS-RT now also initialises a snapshot during instantiation.

Further work

While using a base class has improved encapsulation and the separation of input mapping code from "framework code" (many fields are now private to the base class), the buffer is still very much exposed. In further work I would like to improve this further by totally encapsulating the buffer.

In the end I see design like the following:

• split Siri/GTFS-RT updating code from the management of the snapshots
• instead of base class, there is a timetable snapshot manager taking care of buffering and snapshoting
• there is only one snapshot manager per transit model
• the Siri/GTFS-RT updaters have a reference to this snapshot manager
• Siri/GTFS-RT updaters can then update the snapshots sequentially

Unit tests

Unit tests were updated. Slight modifications were necessary.

Other work

#5852 and #5726 also touch on very similar code and I will wait until they are merged before requesting a code review.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 68.49%. Comparing base (8f632f1) to head (2d86fc6).
Report is 1 commits behind head on dev-2.x.

Files	Patch %	Lines
.../updater/trip/AbstractTimetableSnapshotSource.java	95.34%	1 Missing and 1 partial ⚠️
...pplanner/ext/siri/SiriTimetableSnapshotSource.java	85.71%	1 Missing ⚠️
...a/org/opentripplanner/model/TimetableSnapshot.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #5853      +/-   ##
=============================================
+ Coverage      68.47%   68.49%   +0.01%     
- Complexity     16698    16703       +5     
=============================================
  Files           1914     1915       +1     
  Lines          72673    72652      -21     
  Branches        7454     7447       -7     
=============================================
- Hits           49763    49760       -3     
+ Misses         20340    20326      -14     
+ Partials        2570     2566       -4     

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[leonardehrenfried]

I've now rebased onto dev-2.x which contains @habrahamsson-skanetrafiken's Siri tests and they all still pass.

[habrahamsson-skanetrafiken]

Thanks for making this as easy to review as possible! It looks like a good first step in unifying the snapshot stuff.

[vpaturet]

This looks good. Just a few typos.