xptracker: support xp gains when offline

When xp is gained when offline, the tracker calculates it into the
xp/hr, which can lead to very skewed stats due to the tracker being
generally paused when the player is offline.

This offsets the start xp by the gains when offline to correct for it.

runelite-client/src/main/java/net/runelite/client/plugins/xptracker/XpStateSingle.java

@@ -28,21 +28,20 @@ package net.runelite.client.plugins.xptracker;
 import java.util.HashMap;
 import java.util.Map;
 import lombok.Getter;
-import lombok.RequiredArgsConstructor;
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 import net.runelite.api.Experience;
 import net.runelite.api.Skill;
 
 @Slf4j
-@RequiredArgsConstructor
 class XpStateSingle
 {
 	private final Skill skill;
 	private final Map<XpActionType, XpAction> actions = new HashMap<>();
 
 	@Getter
-	private final long startXp;
+	@Setter
+	private long startXp;
 
 	@Getter
 	private int xpGained = 0;
@@ -54,13 +53,19 @@ class XpStateSingle
 	private int startLevelExp = 0;
 	private int endLevelExp = 0;
 
+	XpStateSingle(Skill skill, long startXp)
+	{
+		this.skill = skill;
+		this.startXp = startXp;
+	}
+
 	XpAction getXpAction(final XpActionType type)
 	{
 		actions.putIfAbsent(type, new XpAction());
 		return actions.get(type);
 	}
 
-	private long getCurrentXp()
+	long getCurrentXp()
 	{
 		return startXp + xpGained;
 	}

runelite-client/src/main/java/net/runelite/client/plugins/xptracker/XpTrackerPlugin.java

@@ -391,6 +391,32 @@ public class XpTrackerPlugin extends Plugin
 		{
 			initializeTracker = false;
 
+			// Check for xp gained while logged out
+			for (Skill skill : Skill.values())
+			{
+				if (skill == Skill.OVERALL || !xpState.isInitialized(skill))
+				{
+					continue;
+				}
+
+				XpStateSingle skillState = xpState.getSkill(skill);
+				final int currentXp = client.getSkillExperience(skill);
+				if (skillState.getCurrentXp() != currentXp)
+				{
+					if (currentXp < skillState.getCurrentXp())
+					{
+						log.debug("Xp is going backwards! {} {} -> {}", skill, skillState.getCurrentXp(), currentXp);
+						resetState();
+						break;
+					}
+
+					log.debug("Skill xp for {} changed when offline: {} -> {}", skill, skillState.getCurrentXp(), currentXp);
+					// Offset start xp for offline gains
+					long diff = skillState.getCurrentXp() - currentXp;
+					skillState.setStartXp(skillState.getStartXp() + diff);
+				}
+			}
+
 			// Initialize the tracker with the initial xp if not already initialized
 			for (Skill skill : Skill.values())
 			{