feat(train): a workout out as GPX, TCX or FIT (ADR 0030, D49)

11b: Export on a workout's page hands it to the share sheet as GPX (with
a track only; heart rate and cadence in Garmin's TrackPointExtension),
TCX (laps, heart rate, cadence, watts, a row's distance) or FIT (file
ID, records, timer events at the pauses, laps with their intensities,
session, activity), all from the same points: the precise fixes while
moving, else the rower's frames, else the heart rates; a plan's steps
are the laps. The FIT writer is our own (protocol 1.0, CRC-16/ARC),
tested by a reader written from the specification.

Not tried yet with Strava, intervals.icu or Garmin Connect.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/train/halkyon_train_flutter/test/support/fake_route_files.dart

@@ -4,7 +4,8 @@ import 'dart:typed_data';
 import 'package:halkyon_train_flutter/src/feature/route/data/route_files.dart';
 
 /// [RouteFiles] in memory: the file [picked] next, files handed over with
-/// [open], and the files shared kept in [shared].
+/// [open], and the files shared kept in [shared], their types in
+/// [sharedTypes].
 class FakeRouteFiles({@override final bool shares = true})
     implements RouteFiles {
   final _opened = StreamController<OpenedFile>.broadcast();
@@ -13,6 +14,7 @@ class FakeRouteFiles({@override final bool shares = true})
   OpenedFile? picked;
 
   final shared = <OpenedFile>[];
+  final sharedTypes = <String>[];
 
   /// A file opened with Train or shared to it.
   void open(OpenedFile file) => _opened.add(file);
@@ -24,8 +26,13 @@ class FakeRouteFiles({@override final bool shares = true})
   Future<OpenedFile?> pick() async => picked;
 
   @override
-  Future<bool> share({required String name, required Uint8List bytes}) async {
+  Future<bool> share({
+    required String name,
+    required Uint8List bytes,
+    String mimeType = gpxMimeType,
+  }) async {
     shared.add((name: name, bytes: bytes));
+    sharedTypes.add(mimeType);
     return true;
   }
 }

apps/train/halkyon_train_flutter/test/support/fit_reader.dart

@@ -0,0 +1,74 @@
+import 'dart:typed_data';
+
+import 'package:halkyon_train_flutter/src/feature/workout/data/fit_encoder.dart';
+
+/// A FIT message as read: its global number and its fields' values by
+/// number, invalid values left out.
+typedef FitMessage = ({int global, Map<int, int> fields});
+
+/// Reads a FIT file as the FIT SDK's protocol 1.0 lays it out, written
+/// from its specification apart from [FitWriter]: the header and the file's
+/// CRC checked, each definition (little-endian only) and the messages of
+/// normal headers; throws a [FormatException] on anything else.
+List<FitMessage> readFit(Uint8List bytes) {
+  final data = ByteData.sublistView(bytes);
+  final headerSize = bytes[0];
+  if (headerSize != 14 || String.fromCharCodes(bytes, 8, 12) != '.FIT') {
+    throw const FormatException('Not a FIT header');
+  }
+  if (data.getUint16(12, Endian.little) != fitCrc(bytes.sublist(0, 12))) {
+    throw const FormatException("The header's CRC");
+  }
+  final size = data.getUint32(4, Endian.little);
+  if (bytes.length != headerSize + size + 2) {
+    throw const FormatException("The data's size");
+  }
+  final end = headerSize + size;
+  if (data.getUint16(end, Endian.little) != fitCrc(bytes.sublist(0, end))) {
+    throw const FormatException("The file's CRC");
+  }
+  final definitions = <int, ({int global, List<(int, int, int)> fields})>{};
+  final messages = <FitMessage>[];
+  var at = headerSize;
+  while (at < end) {
+    final header = bytes[at++];
+    if (header & 0x80 != 0) {
+      throw const FormatException('A compressed timestamp');
+    }
+    final local = header & 0x0F;
+    if (header & 0x40 != 0) {
+      if (bytes[at + 1] != 0) {
+        throw const FormatException('Big-endian');
+      }
+      final global = data.getUint16(at + 2, Endian.little);
+      final count = bytes[at + 4];
+      at += 5;
+      definitions[local] = (
+        global: global,
+        fields: [
+          for (var i = 0; i < count; i++)
+            (bytes[at + i * 3], bytes[at + i * 3 + 1], bytes[at + i * 3 + 2]),
+        ],
+      );
+      at += count * 3;
+      continue;
+    }
+    final definition = definitions[local]!;
+    final fields = <int, int>{};
+    for (final (number, size, base) in definition.fields) {
+      final (value, invalid) = switch ((base, size)) {
+        (0x00 || 0x02, 1) => (bytes[at], 0xFF),
+        (0x84, 2) => (data.getUint16(at, Endian.little), 0xFFFF),
+        (0x85, 4) => (data.getInt32(at, Endian.little), 0x7FFFFFFF),
+        (0x86, 4) => (data.getUint32(at, Endian.little), 0xFFFFFFFF),
+        _ => throw FormatException('Base type $base of $size bytes'),
+      };
+      if (value != invalid) {
+        fields[number] = value;
+      }
+      at += size;
+    }
+    messages.add((global: definition.global, fields: fields));
+  }
+  return messages;
+}