From dbba1c1607ec97f1195c038c065b0b376ab5a2f6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ullrich=20Sch=C3=A4fer?= <hi+github@ullrich.is>
Date: Fri, 1 May 2026 10:24:50 +0200
Subject: [PATCH] Fix FIT Course capabilities and lap duration

The Course message advertised capabilities=0x04 (time only), telling
consumers the course had no position data. Wahoo accepted the route
(distance/elevation come from request fields) but rendered an empty
map. Set capabilities to valid|distance|position (0x1A).

Also write a real lap totalElapsedTime/totalTimerTime derived from the
1Hz record timestamps; a zero-duration lap can be rejected as malformed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
---
 packages/fit/src/gpx-to-fit-course.test.ts | 35 ++++++++++++++++++++--
 packages/fit/src/gpx-to-fit-course.ts      | 18 +++++++++--
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/packages/fit/src/gpx-to-fit-course.test.ts b/packages/fit/src/gpx-to-fit-course.test.ts
index 8607f3d..6f938ea 100644
--- a/packages/fit/src/gpx-to-fit-course.test.ts
+++ b/packages/fit/src/gpx-to-fit-course.test.ts
@@ -17,8 +17,10 @@ async function loadFixture(name: string): Promise<string> {
 
 interface ParsedFit {
   records: Array<{ position_lat?: number; position_long?: number; altitude?: number }>;
-  course?: Array<{ name?: string; sport?: string }> | { name?: string; sport?: string };
-  laps?: Array<unknown>;
+  course?:
+    | Array<{ name?: string; sport?: string; capabilities?: unknown }>
+    | { name?: string; sport?: string; capabilities?: unknown };
+  laps?: Array<{ total_elapsed_time?: number; total_timer_time?: number }>;
 }
 
 function decode(bytes: Uint8Array): Promise<ParsedFit> {
@@ -65,6 +67,35 @@ describe("gpxToFitCourse", () => {
     await expect(gpxToFitCourse({ gpx, name: "Empty" })).rejects.toThrow(/zero track points/);
   });
 
+  it("advertises position+distance course capabilities (not time-only)", async () => {
+    const gpx = await loadFixture("short-flat.gpx");
+    const bytes = await gpxToFitCourse({ gpx, name: "Caps", sport: "cycling" });
+    const parsed = await decode(bytes);
+    const course = Array.isArray(parsed.course) ? parsed.course[0] : parsed.course;
+    // fit-file-parser returns capabilities as a single-element array of the raw bitfield.
+    const caps = course?.capabilities;
+    const value = Array.isArray(caps) ? Number(caps[0]) : Number(caps);
+    const VALID = 0x02;
+    const DISTANCE = 0x08;
+    const POSITION = 0x10;
+    const TIME = 0x04;
+    expect(value & VALID).toBe(VALID);
+    expect(value & DISTANCE).toBe(DISTANCE);
+    expect(value & POSITION).toBe(POSITION);
+    expect(value & TIME).toBe(0);
+  });
+
+  it("writes a non-zero lap elapsed time matching record count", async () => {
+    const gpx = await loadFixture("short-flat.gpx");
+    const source = await parseGpxAsync(gpx);
+    const sourcePoints = source.tracks.flat();
+    const bytes = await gpxToFitCourse({ gpx, name: "Lap", sport: "cycling" });
+    const parsed = await decode(bytes);
+    const lap = parsed.laps?.[0];
+    expect(lap?.total_elapsed_time).toBe(sourcePoints.length - 1);
+    expect(lap?.total_timer_time).toBe(sourcePoints.length - 1);
+  });
+
   it("encodes course name and sport", async () => {
     const gpx = await loadFixture("short-flat.gpx");
     const bytes = await gpxToFitCourse({ gpx, name: "Loop Test", sport: "cycling" });
diff --git a/packages/fit/src/gpx-to-fit-course.ts b/packages/fit/src/gpx-to-fit-course.ts
index 7f877eb..d8065f5 100644
--- a/packages/fit/src/gpx-to-fit-course.ts
+++ b/packages/fit/src/gpx-to-fit-course.ts
@@ -49,13 +49,25 @@ export async function gpxToFitCourse(input: GpxToFitCourseInput): Promise<Uint8A
     hardwareVersion: 0,
   });
 
+  // courseCapabilities bitfield (FIT Profile):
+  //   0x02 valid | 0x08 distance | 0x10 position
+  // Previously this was 0x04 ("time" only), which falsely told consumers the
+  // course had no position data — Wahoo accepted the route but rendered an
+  // empty map.
+  const COURSE_CAPABILITIES_VALID_DISTANCE_POSITION = 0x1a;
+
   encoder.writeMesg({
     mesgNum: Profile.MesgNum.COURSE,
     name: input.name,
     sport: SPORT_ENUM[input.sport ?? "cycling"],
-    capabilities: 0x00000004,
+    capabilities: COURSE_CAPABILITIES_VALID_DISTANCE_POSITION,
   });
 
+  // Records below are written at 1Hz starting at startTime, so elapsed time
+  // matches (points.length - 1) seconds. A zero-duration lap can be rejected
+  // as malformed by stricter consumers.
+  const totalElapsedSeconds = points.length - 1;
+
   encoder.writeMesg({
     mesgNum: Profile.MesgNum.LAP,
     timestamp: startTime,
@@ -64,8 +76,8 @@ export async function gpxToFitCourse(input: GpxToFitCourseInput): Promise<Uint8A
     startPositionLong: degToSemicircles(first.lon),
     endPositionLat: degToSemicircles(last.lat),
     endPositionLong: degToSemicircles(last.lon),
-    totalElapsedTime: 0,
-    totalTimerTime: 0,
+    totalElapsedTime: totalElapsedSeconds,
+    totalTimerTime: totalElapsedSeconds,
     totalDistance: data.distance,
   });