[epilogue] Measure unit metadata

epilogue-runtime/src/main/java/edu/wpi/first/epilogue/logging/EpilogueBackend.java

@@ -193,12 +193,24 @@ default <S> void log(String identifier, Collection<S> value, Struct<S> struct) {
     log(identifier, array, struct);
   }
 
+  /**
+   * Logs a unit's symbol.
+   *
+   * @param identifier the identifier of the data field
+   * @param value the new value of the data field
+   */
+  default void log(String identifier, Unit value) {
+    log(identifier, value.symbol());
+  }
+
   /**
    * Logs a measurement's value in terms of its base unit.
    *
+   * <p>If the base unit is different from a prior call with the same identifier the value will be
+   * ignored.
+   *
    * @param identifier the identifier of the data field
    * @param value the new value of the data field
-   * @param <U> the dimension of the unit
    */
   default <U extends Unit> void log(String identifier, Measure<U> value) {
     log(identifier, value, value.baseUnit());
@@ -213,7 +225,7 @@ default <U extends Unit> void log(String identifier, Measure<U> value) {
    * @param <U> the dimension of the unit
    */
   default <U extends Unit> void log(String identifier, Measure<U> value, U unit) {
-    log(identifier + " (" + unit.symbol() + ")", value.in(unit));
+    log(identifier, value.in(unit));
   }
 
   /**

epilogue-runtime/src/main/java/edu/wpi/first/epilogue/logging/FileBackend.java

@@ -6,6 +6,8 @@
 
 import static edu.wpi.first.util.ErrorMessages.requireNonNullParam;
 
+import edu.wpi.first.units.Measure;
+import edu.wpi.first.units.Unit;
 import edu.wpi.first.util.datalog.BooleanArrayLogEntry;
 import edu.wpi.first.util.datalog.BooleanLogEntry;
 import edu.wpi.first.util.datalog.DataLog;
@@ -31,6 +33,7 @@ public class FileBackend implements EpilogueBackend {
   private final DataLog m_dataLog;
   private final Map<String, DataLogEntry> m_entries = new HashMap<>();
   private final Map<String, NestedBackend> m_subLoggers = new HashMap<>();
+  private final Map<String, Unit> m_units = new HashMap<>();
 
   /**
    * Creates a new file-based backend.
@@ -141,4 +144,15 @@ public <S> void log(String identifier, S[] value, Struct<S> struct) {
     m_dataLog.addSchema(struct);
     getEntry(identifier, (log, k) -> StructArrayLogEntry.create(log, k, struct)).append(value);
   }
+
+  @Override
+  public <U extends Unit> void log(String identifier, Measure<U> value, U unit) {
+    DoubleLogEntry entry = getEntry(identifier, DoubleLogEntry::new);
+    entry.append(value.in(unit));
+    Unit cachedUnit = m_units.get(identifier);
+    if (m_units.containsKey(identifier) || !cachedUnit.equivalent(unit)) {
+      entry.setMetadata("{ \"unit\": \"" + unit.symbol() + "\" }");
+      m_units.put(identifier, unit);
+    }
+  }
 }

epilogue-runtime/src/main/java/edu/wpi/first/epilogue/logging/NTEpilogueBackend.java

@@ -19,6 +19,8 @@
 import edu.wpi.first.networktables.StringPublisher;
 import edu.wpi.first.networktables.StructArrayPublisher;
 import edu.wpi.first.networktables.StructPublisher;
+import edu.wpi.first.units.Measure;
+import edu.wpi.first.units.Unit;
 import edu.wpi.first.util.struct.Struct;
 import java.util.HashMap;
 import java.util.Map;
@@ -32,6 +34,7 @@ public class NTEpilogueBackend implements EpilogueBackend {
 
   private final Map<String, Publisher> m_publishers = new HashMap<>();
   private final Map<String, NestedBackend> m_nestedBackends = new HashMap<>();
+  private final Map<String, Unit> m_units = new HashMap<>();
 
   /**
    * Creates a logging backend that sends information to NetworkTables.
@@ -164,4 +167,17 @@ public <S> void log(String identifier, S[] value, Struct<S> struct) {
                 identifier, k -> m_nt.getStructArrayTopic(k, struct).publish()))
         .set(value);
   }
+
+  @Override
+  public <U extends Unit> void log(String identifier, Measure<U> value, U unit) {
+    DoublePublisher pub =
+        (DoublePublisher)
+            m_publishers.computeIfAbsent(identifier, k -> m_nt.getDoubleTopic(k).publish());
+    pub.set(value.in(unit));
+    Unit cachedUnit = m_units.get(identifier);
+    if (cachedUnit == null || !cachedUnit.equivalent(unit)) {
+      pub.getTopic().setProperty(identifier, identifier);
+      m_units.put(identifier, unit);
+    }
+  }
 }