DB: support "best price search"

[derhuerst]

Both the Deutsche Bahn (DB) website as well as their app have a feature called "best price search" or "Bestpreissuche", which works just like the regular journeys() (TripSearch in HAFAS), except that it returns the lowest-price journeys for each time bracket.

The details of this BestPriceSearch call are documented at juliuste/db-prices#33 (comment) . It's response data looks like the one of a TripSearch call, but it also has a field res.outDaySegL that groups the journeys in res.outConL[] into time brackets.

Not sure how this functionality should be exposed:

• We could let journeys() always parse & expose a grouping/bracketing of journeys as soon as the HAFAS response contains it. A DB-specific opt.bestPriceSearch option would use BestPriceSearch and outTime: "000000".
• Within the DB profile, we could implement it as an entirely separate hafas-client method. It would have to share much of the logic with journeys(). Currently, we don't have a mechanism to let profiles add methods though.

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pyhafas equivalent Issue: FahrplanDatenGarten/pyhafas#26

[derhuerst]

@TheRealMurmel FYI: Implementing the "best price search" feature here in hafas-client, as described above, would be quite straightforward, as most of the response structure is already supported.

[TheRealMurmel]

@derhuerst I would really like to provide more help, but I'm note quite sure when I will have time to contribute here.

[TheRealMurmel]

@derhuerst I built a small Python-based project to replay the relevant API requests, this might help someone else to re-implement the requests into hafas-client:

https://github.com/TheRealMurmel/py-bahn-api

[derhuerst]

BTW, if you're more comfortable tinkering with Python instead of JS, adding support for "best price search" to pyhafas would also be an option! We can then port the code over to hafas-client.

[TheRealMurmel]

I'll give it a try!

[derhuerst]

@bergmannjg has built an "MVP" implementation of this.

[bergmannjg]

@bergmannjg has built an "MVP" implementation of this.

It's nothing more than replacing

meth: "TripSearch"

with

meth: "BestPriceSearch"

in the corresponding HAFAS request.

It works.

[bergmannjg]

@derhuerst said

Not sure how this functionality should be exposed:

• We could let journeys() always parse & expose a grouping/bracketing of journeys as soon as the HAFAS response contains it. A DB-specific opt.bestPriceSearch option would use BestPriceSearch and outTime: "000000".
• Within the DB profile, we could implement it as an entirely separate hafas-client method. It would have to share much of the logic with journeys(). Currently, we don't have a mechanism to let profiles add methods though.

I would propose to add an new method to the hafas-client API because the bestprice search options are only a subset of the journey search options and the results are different.

Here is my (not yet complete) implementation

• there is a new bestPrices method, which is only valid for the db profile
• the parsed value of the res.outDaySegL array is the result of bestPrices
• a first unit test is in db-bestprice.js

[thigg]

Is this planned to be merged? / worked on?

Here is my (not yet complete) implementation

[thigg]

I am running this for a few days already without problems, just added the date as a parameter.

[derhuerst]

remotely related: #331