Add first person spectator keyframes to simplepathing

src/main/java/com/replaymod/pathing/properties/SpectatorProperty.java

@@ -0,0 +1,51 @@
+package com.replaymod.pathing.properties;
+
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import com.replaymod.replay.ReplayHandler;
+import com.replaymod.replaystudio.pathing.property.AbstractProperty;
+import com.replaymod.replaystudio.pathing.property.PropertyPart;
+import com.replaymod.replaystudio.pathing.property.PropertyParts;
+import lombok.NonNull;
+import net.minecraft.entity.Entity;
+import net.minecraft.world.World;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Collections;
+
+/**
+ * Property for the camera spectating an entity.
+ */
+public class SpectatorProperty extends AbstractProperty<Integer> {
+    public static final SpectatorProperty PROPERTY = new SpectatorProperty();
+    public final PropertyPart<Integer> ENTITY_ID = new PropertyParts.ForInteger(this, false);
+    private SpectatorProperty() {
+        super("spectate", "replaymod.gui.playeroverview.spectate", null, -1);
+    }
+
+    @Override
+    public Collection<PropertyPart<Integer>> getParts() {
+        return Collections.singletonList(ENTITY_ID);
+    }
+
+    @Override
+    public void applyToGame(Integer value, @NonNull Object replayHandler) {
+        ReplayHandler handler = ((ReplayHandler) replayHandler);
+        World world = handler.getCameraEntity().getEntityWorld();
+        // Lookup entity by id, returns null if an entity with the id does not exists
+        Entity target = world.getEntityByID(value);
+        // Spectate entity, when called with null, returns to camera
+        handler.spectateEntity(target);
+    }
+
+    @Override
+    public void toJson(JsonWriter writer, Integer value) throws IOException {
+        writer.value(value);
+    }
+
+    @Override
+    public Integer fromJson(JsonReader reader) throws IOException {
+        return reader.nextInt();
+    }
+}