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trails/openspec/changes/planner-route-encoding/tasks.md
Ullrich Schäfer b81108b10b
feat(map-core): compact route codec (polyline + RLE) for planner doc 
Task group 1 of planner-route-encoding. Framework-free `route-codec.ts`:
- encodePolyline/decodePolyline — fixed-precision (1e5) delta + zig-zag
  varint + base64; lossless to ~1 m, version-tagged ("p1:").
- encodeRuns/decodeRuns — run-length codec for the per-coordinate
  road-metadata channels, tagged ("r1:").
- isEncodedPolyline/isEncodedRuns — so the read path (group 3) tells the
  new encoding apart from legacy JSON.

Not yet wired into route-data.ts (groups 2–3). Verified: map-core
typecheck + lint clean, 52/52 tests (round-trip within 1 m, empty/single,
RLE collapse, >3x smaller than JSON).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
2026-07-15 16:55:34 +02:00

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1. Codec primitives

  • 1.1 Add a framework-free codec in @trails-cool/map-core (e.g. route-codec.ts): encodePolyline(coords: [lon,lat][]) -> string / decodePolyline(str) -> [lon,lat][] using fixed-precision (1e5) delta + zig-zag varint + base64, with a version tag
  • 1.2 Add encodeRuns(values: string[]) -> string / decodeRuns(str, length?) -> string[] run-length codec for the road-metadata channels
  • 1.3 Unit tests: polyline round-trip within ~1 m over random + real fixtures; empty/single-point; RLE round-trip incl. all-same, all-distinct, and a realistic run pattern

2. Write path (new encoding)

  • 2.1 In route-data.ts writeComputedRoute: store geometry once as encodePolyline(coordinates) (drop the separate geojson write); write each ROAD_METADATA_KEYS channel via encodeRuns; keep segmentBoundaries + profile
  • 2.2 Add a readGeojson(routeData) helper that assembles the GeoJSON LineString from decoded coordinates (so callers that needed geojson no longer read a stored copy)

3. Read path (dual-format, backward compatible)

  • 3.1 In route-data.ts read helpers (readComputedRoute, readRoadMetadata, coordinate accessors): detect format per key (encoding version tag/sentinel → new decoder; else JSON.parse legacy) and return the same decoded shapes as today
  • 3.2 Point every reader (SessionView map render, elevation profile, GPX export, save-to-journal, road-type/surface coloring) at the helpers; confirm none reads a raw routeData.get("geojson"|"coordinates"|<metadata>) directly
  • 3.3 Tests: a legacy-format routeData decodes correctly through the helpers; a new-format one decodes correctly; both yield identical reader-facing data

4. Verification

  • 4.1 GPX-export golden test: export the same route via legacy and new encoding → byte-identical output
  • 4.2 Size assertion on a realistic route fixture (e.g. the ~77 km / multi-waypoint case): new-encoded Y.encodeStateAsUpdate size is ≥~4× smaller than legacy and a small fraction of MAX_DOC_BYTES
  • 4.3 Confirm routing-host election / BRouter usage unchanged (no client recompute); pnpm --filter @trails-cool/planner --filter @trails-cool/map-core typecheck && lint && test, full pnpm test
  • 4.4 Manual/e2e sanity: open a fresh session, add several waypoints, confirm route renders + colors + exports; reload a session persisted in the legacy format and confirm it still works