WIP

src/androidTest/java/de/dennisguse/opentracks/io/file/exporter/FITv2TrackExporterTest.java

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+package de.dennisguse.opentracks.io.file.exporter;
+
+import org.junit.Test;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+public class FITv2TrackExporterTest {
+
+    private final byte FIT_PROTOCOL_VERSION = 2 << 4 + 0;
+    private final short FIT_PROFILE_VERSION = 21 * 1000 + 158;
+
+    private long checksum;
+    private final byte FILE_HEADER_SIZE = 14;
+
+    @Test
+    public void run() {
+        ByteBuffer littleEndian = ByteBuffer
+                .allocate(FILE_HEADER_SIZE)
+                .order(ByteOrder.LITTLE_ENDIAN);
+
+        littleEndian.put(0, FILE_HEADER_SIZE);
+        littleEndian.put(1, FIT_PROTOCOL_VERSION);
+
+        // Profile version: 1513
+        littleEndian.putShort(2, FIT_PROFILE_VERSION);
+
+        // Data size: 32bit
+        littleEndian.putInt(4, 0); // We do not calculate the data size.
+
+        // .FIT
+        littleEndian.putChar(8, '.');
+        littleEndian.putChar(9, 'F');
+        littleEndian.putChar(10, 'I');
+        littleEndian.putChar(11, 'T');
+
+        // CRC (not implemented)
+        littleEndian.put(12, (byte) 0);
+        littleEndian.put(13, (byte) 0);
+
+        var a = littleEndian.array();
+        littleEndian.array();
+    }
+}

src/main/java/de/dennisguse/opentracks/io/file/exporter/FITv2TrackExporter.java

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+package de.dennisguse.opentracks.io.file.exporter;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.VisibleForTesting;
+
+import java.io.OutputStream;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.channels.Channels;
+import java.nio.channels.WritableByteChannel;
+import java.util.List;
+
+import de.dennisguse.opentracks.data.models.Track;
+
+/**
+ * FIT v2.0
+ * https://developer.garmin.com/fit/
+ * <p>
+ * Encoding is little endian.
+ */
+public class FITv2TrackExporter implements TrackExporter {
+
+    private final byte FIT_PROTOCOL_VERSION = 2 << 4 + 0;
+    private final short FIT_PROFILE_VERSION = 21 * 1000 + 158;
+
+    private long checksum;
+    private final byte FILE_HEADER_SIZE = 14;
+
+
+    @Override
+    public boolean writeTrack(List<Track> tracks, @NonNull OutputStream outputStream) {
+        WritableByteChannel channel = Channels.newChannel(outputStream);
+
+        writeFileHeader(channel);
+        // writeFileId(channel);
+        writeFooter(channel);
+        return false;
+    }
+
+    // https://developer.garmin.com/fit/protocol/
+    @VisibleForTesting
+    void writeFileHeader(@NonNull WritableByteChannel channel) {
+        ByteBuffer littleEndian = ByteBuffer
+                .allocate(FILE_HEADER_SIZE)
+                .order(ByteOrder.LITTLE_ENDIAN);
+
+        littleEndian.put(0, FILE_HEADER_SIZE);
+        littleEndian.put(1, FIT_PROTOCOL_VERSION);
+
+        // Profile version
+        littleEndian.putShort(2, FIT_PROFILE_VERSION);
+
+        // Data size: 32bit
+        littleEndian.putInt(4, 0); // We do not calculate the data size.
+
+        // .FIT
+        littleEndian.putChar(8, '.');
+        littleEndian.putChar(9, 'F');
+        littleEndian.putChar(10, 'I');
+        littleEndian.putChar(11, 'T');
+
+        // CRC (not implemented)
+        littleEndian.put(12, (byte) 0);
+        littleEndian.put(13, (byte) 0);
+
+        var a = littleEndian.array();
+        littleEndian.array();
+    }
+
+
+    private void writeFooter(@NonNull WritableByteChannel channel) {
+
+    }
+}