Add the ability to make town and nation ranks require a town or nation level.

Towny/src/main/java/com/palmergames/bukkit/towny/db/TownyFlatFileSource.java

@@ -2030,8 +2030,8 @@ public boolean saveResident(Resident resident) {
 
 		if (resident.hasTown()) {
 			list.add("town=" + resident.getTownOrNull().getName());
-			list.add("town-ranks=" + StringMgmt.join(resident.getTownRanks(), ","));
-			list.add("nation-ranks=" + StringMgmt.join(resident.getNationRanks(), ","));
+			list.add("town-ranks=" + StringMgmt.join(resident.getTownRanksForSaving(), ","));
+			list.add("nation-ranks=" + StringMgmt.join(resident.getNationRanksForSaving(), ","));
 		}
 
 		// Friends

Towny/src/main/java/com/palmergames/bukkit/towny/db/TownySQLSource.java

@@ -2312,8 +2312,8 @@ public synchronized boolean saveResident(Resident resident) {
 			if (!TownySettings.getDefaultResidentAbout().equals(resident.getAbout()))
 				res_hm.put("about", resident.getAbout());
 			res_hm.put("town", resident.hasTown() ? resident.getTown().getName() : "");
-			res_hm.put("town-ranks", resident.hasTown() ? StringMgmt.join(resident.getTownRanks(), "#") : "");
-			res_hm.put("nation-ranks", resident.hasTown() ? StringMgmt.join(resident.getNationRanks(), "#") : "");
+			res_hm.put("town-ranks", resident.hasTown() ? StringMgmt.join(resident.getTownRanksForSaving(), "#") : "");
+			res_hm.put("nation-ranks", resident.hasTown() ? StringMgmt.join(resident.getNationRanksForSaving(), "#") : "");
 			res_hm.put("friends", StringMgmt.join(resident.getFriends(), "#"));
 			res_hm.put("protectionStatus", resident.getPermissions().toString().replaceAll(",", "#"));
 

Towny/src/main/java/com/palmergames/bukkit/towny/event/nation/NationLevelDecreaseEvent.java

@@ -0,0 +1,36 @@
+package com.palmergames.bukkit.towny.event.nation;
+
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+
+import com.palmergames.bukkit.towny.object.Nation;
+
+public class NationLevelDecreaseEvent extends Event {
+
+	private static final HandlerList handlers = new HandlerList();
+	private final Nation nation;
+
+	public NationLevelDecreaseEvent(Nation nation) {
+		super(!Bukkit.getServer().isPrimaryThread());
+		this.nation = nation;
+	}
+
+	@Override
+	public HandlerList getHandlers() {
+		return handlers;
+	}
+
+	public static HandlerList getHandlerList() {
+		return handlers;
+	}
+
+	/**
+	 * The nation which has had its Nation_Level decrease.
+	 * 
+	 * @return nation which has had its Nation_Level decrease.
+	 */
+	public Nation getNation() {
+		return nation;
+	}
+}

Towny/src/main/java/com/palmergames/bukkit/towny/event/nation/NationLevelIncreaseEvent.java

@@ -0,0 +1,36 @@
+package com.palmergames.bukkit.towny.event.nation;
+
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+
+import com.palmergames.bukkit.towny.object.Nation;
+
+public class NationLevelIncreaseEvent extends Event {
+
+	private static final HandlerList handlers = new HandlerList();
+	private final Nation nation;
+
+	public NationLevelIncreaseEvent(Nation nation) {
+		super(!Bukkit.getServer().isPrimaryThread());
+		this.nation = nation;
+	}
+
+	@Override
+	public HandlerList getHandlers() {
+		return handlers;
+	}
+
+	public static HandlerList getHandlerList() {
+		return handlers;
+	}
+
+	/**
+	 * The nation which has had its Nation_Level increase.
+	 * 
+	 * @return nation which has had its Nation_Level increase.
+	 */
+	public Nation getNation() {
+		return nation;
+	}
+}

Towny/src/main/java/com/palmergames/bukkit/towny/event/town/TownLevelDecreaseEvent.java

@@ -0,0 +1,36 @@
+package com.palmergames.bukkit.towny.event.town;
+
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+
+import com.palmergames.bukkit.towny.object.Town;
+
+public class TownLevelDecreaseEvent extends Event {
+
+	private static final HandlerList handlers = new HandlerList();
+	private final Town town;
+
+	public TownLevelDecreaseEvent(Town town) {
+		super(!Bukkit.getServer().isPrimaryThread());
+		this.town = town;
+	}
+
+	@Override
+	public HandlerList getHandlers() {
+		return handlers;
+	}
+
+	public static HandlerList getHandlerList() {
+		return handlers;
+	}
+
+	/**
+	 * The town which has had its Town_Level decrease.
+	 * 
+	 * @return town which has had its Town_Level decrease.
+	 */
+	public Town getTown() {
+		return town;
+	}
+}

Towny/src/main/java/com/palmergames/bukkit/towny/event/town/TownLevelIncreaseEvent.java

@@ -0,0 +1,36 @@
+package com.palmergames.bukkit.towny.event.town;
+
+import org.bukkit.Bukkit;
+import org.bukkit.event.Event;
+import org.bukkit.event.HandlerList;
+
+import com.palmergames.bukkit.towny.object.Town;
+
+public class TownLevelIncreaseEvent extends Event {
+
+	private static final HandlerList handlers = new HandlerList();
+	private final Town town;
+
+	public TownLevelIncreaseEvent(Town town) {
+		super(!Bukkit.getServer().isPrimaryThread());
+		this.town = town;
+	}
+
+	@Override
+	public HandlerList getHandlers() {
+		return handlers;
+	}
+
+	public static HandlerList getHandlerList() {
+		return handlers;
+	}
+
+	/**
+	 * The town which has had its Town_Level increase.
+	 * 
+	 * @return town which has had its Town_Level increase.
+	 */
+	public Town getTown() {
+		return town;
+	}
+}

Towny/src/main/java/com/palmergames/bukkit/towny/listeners/TownyCustomListener.java

@@ -21,11 +21,16 @@
 import com.palmergames.bukkit.towny.event.TownPreAddResidentEvent;
 import com.palmergames.bukkit.towny.event.TownRemoveResidentEvent;
 import com.palmergames.bukkit.towny.event.damage.TownyPlayerDamagePlayerEvent;
+import com.palmergames.bukkit.towny.event.nation.NationLevelDecreaseEvent;
+import com.palmergames.bukkit.towny.event.nation.NationLevelIncreaseEvent;
 import com.palmergames.bukkit.towny.event.nation.NationPreTownLeaveEvent;
+import com.palmergames.bukkit.towny.event.town.TownLevelDecreaseEvent;
+import com.palmergames.bukkit.towny.event.town.TownLevelIncreaseEvent;
 import com.palmergames.bukkit.towny.event.town.TownPreUnclaimCmdEvent;
 import com.palmergames.bukkit.towny.event.town.TownPreUnclaimEvent;
 import com.palmergames.bukkit.towny.exceptions.TownyException;
 import com.palmergames.bukkit.towny.object.CellSurface;
+import com.palmergames.bukkit.towny.object.Nation;
 import com.palmergames.bukkit.towny.object.PlayerCache;
 import com.palmergames.bukkit.towny.object.Resident;
 import com.palmergames.bukkit.towny.object.SpawnType;
@@ -35,11 +40,13 @@
 import com.palmergames.bukkit.towny.object.Translatable;
 import com.palmergames.bukkit.towny.object.Translation;
 import com.palmergames.bukkit.towny.object.WorldCoord;
+import com.palmergames.bukkit.towny.permissions.TownyPerms;
 import com.palmergames.bukkit.towny.utils.BorderUtil;
 import com.palmergames.bukkit.towny.utils.ChunkNotificationUtil;
 import com.palmergames.bukkit.towny.utils.PlayerCacheUtil;
 import com.palmergames.bukkit.towny.utils.ProximityUtil;
 import com.palmergames.bukkit.towny.utils.SpawnUtil;
+import com.palmergames.bukkit.util.BukkitTools;
 import com.palmergames.bukkit.util.Colors;
 import com.palmergames.bukkit.util.DrawSmokeTaskFactory;
 import com.palmergames.util.TimeMgmt;
@@ -258,14 +265,27 @@ public void onTownClaim(TownClaimEvent event) {
 	 * Used to warn towns when they've lost a resident, so they know they're at risk
 	 * of having claims stolen in the takeoverclaim feature.
 	 * 
+	 * Used for town_level and nation_level decrease events.
+	 * 
 	 * @param event TownRemoveResidentEvent.
 	 */
 	@EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
 	public void onTownLosesResident(TownRemoveResidentEvent event) {
+		Town town = event.getTown();
+		if (town.getLevelNumber() < TownySettings.getTownLevelFromGivenInt(town.getNumResidents() + 1, town)) {
+			BukkitTools.fireEvent(new TownLevelDecreaseEvent(town));
+		}
+		if (town.hasNation()) {
+			Nation nation = town.getNationOrNull();
+			if (nation.getLevelNumber() < TownySettings.getNationLevelFromGivenInt(nation.getNumResidents() + 1)) {
+				BukkitTools.fireEvent(new NationLevelDecreaseEvent(nation));
+			}	
+		}
+
 		if (!TownySettings.isOverClaimingAllowingStolenLand())
 			return;
-		if (event.getTown().isOverClaimed())
-			TownyMessaging.sendPrefixedTownMessage(event.getTown(), Translatable.literal(Colors.Red).append(Translatable.of("msg_warning_your_town_is_overclaimed")));
+		if (town.isOverClaimed())
+			TownyMessaging.sendPrefixedTownMessage(town, Translatable.literal(Colors.Red).append(Translatable.of("msg_warning_your_town_is_overclaimed")));
 	}
 
 	/**
@@ -312,10 +332,21 @@ public void onResidentPreJoinTown(TownPreAddResidentEvent event) {
 
 	@EventHandler(ignoreCancelled = true)
 	public void onResidentJoinTown(TownAddResidentEvent event) {
+		Town town = event.getTown();
+
+		if (town.getLevelNumber() > TownySettings.getTownLevelFromGivenInt(town.getNumResidents() - 1, town)) {
+			BukkitTools.fireEvent(new TownLevelIncreaseEvent(town));
+		}
+		if (town.hasNation()) {
+			Nation nation = town.getNationOrNull();
+			if (nation.getLevelNumber() > TownySettings.getNationLevelFromGivenInt(nation.getNumResidents() - 1)) {
+				BukkitTools.fireEvent(new NationLevelIncreaseEvent(nation));
+			}	
+		}
+
 		if (!TownySettings.isPromptingNewResidentsToTownSpawn() || !TownySettings.getBoolean(ConfigNodes.SPAWNING_ALLOW_TOWN_SPAWN))
 			return;
 
-		Town town = event.getTown();
 		Player player = event.getResident().getPlayer();
 		Town playerLocationTown = Optional.ofNullable(player).map(p -> TownyAPI.getInstance().getTown(p.getLocation())).orElse(null);
 
@@ -362,4 +393,48 @@ private void attemptPlayerCacheReset(Player player, WorldCoord worldCoord) {
 			return;
 		Towny.getPlugin().resetCache(player);
 	}
+
+	/*
+	 * Watch for town and nation level increasing/decreasing and reassign permissions in case the players have level-requirement permissions. 
+	 */
+
+	@EventHandler
+	public void onTownLevelIncrease(TownLevelIncreaseEvent event) {
+		if (!TownyPerms.ranksWithTownLevelRequirementPresent())
+			return;
+		event.getTown().getResidents()
+		.stream()
+		.filter(Resident::isOnline)
+		.forEach(r -> TownyPerms.assignPermissions(r, r.getPlayer()));
+	}
+
+	@EventHandler
+	public void onTownLevelDecrease(TownLevelDecreaseEvent event) {
+		if (!TownyPerms.ranksWithTownLevelRequirementPresent())
+			return;
+		event.getTown().getResidents()
+		.stream()
+		.filter(Resident::isOnline)
+		.forEach(r -> TownyPerms.assignPermissions(r, r.getPlayer()));
+	}
+
+	@EventHandler
+	public void onNationLevelIncrease(NationLevelIncreaseEvent event) {
+		if (!TownyPerms.ranksWithNationLevelRequirementPresent())
+			return;
+		event.getNation().getResidents()
+		.stream()
+		.filter(Resident::isOnline)
+		.forEach(r -> TownyPerms.assignPermissions(r, r.getPlayer()));
+	}
+
+	@EventHandler
+	public void onNationLevelDecrease(NationLevelDecreaseEvent event) {
+		if (!TownyPerms.ranksWithNationLevelRequirementPresent())
+			return;
+		event.getNation().getResidents()
+		.stream()
+		.filter(Resident::isOnline)
+		.forEach(r -> TownyPerms.assignPermissions(r, r.getPlayer()));
+	}
 }

Towny/src/main/java/com/palmergames/bukkit/towny/object/Resident.java

@@ -593,9 +593,26 @@ public boolean hasTownRank(String rank) {
 	}
 
 	public List<String> getTownRanks() {
+		if (!townRanks.isEmpty() && hasTown()) {
+			ArrayList<String> out = new ArrayList<>();
+			for (String rank : new ArrayList<>(townRanks)) {
+				int requiredTownLevelForRank = TownyPerms.getRankTownLevelReq(rank);
+				if (requiredTownLevelForRank == 0 || getTownOrNull().getLevelNumber() >= requiredTownLevelForRank)
+					out.add(rank);
+			}
+			// Return out modified list of ranks, so that the player will not lose ranks
+			// they've been assigned when their town goes down in a level temporarily. This
+			// ensures they save and load their proper list of ranks.
+			return Collections.unmodifiableList(out);
+		}
 		return Collections.unmodifiableList(townRanks);
 	}
-
+
+	@ApiStatus.Internal
+	public List<String> getTownRanksForSaving() {
+		return Collections.unmodifiableList(townRanks);
+	}
+
 	public boolean removeTownRank(String rank) {
 
 		if (hasTownRank(rank)) {
@@ -646,6 +663,23 @@ public boolean hasNationRank(String rank) {
 	}
 
 	public List<String> getNationRanks() {
+		if (!nationRanks.isEmpty() && hasNation()) {
+			ArrayList<String> out = new ArrayList<>();
+			for (String rank : new ArrayList<>(nationRanks)) {
+				int requiredNationLevelForRank = TownyPerms.getRankTownLevelReq(rank);
+				if (requiredNationLevelForRank == 0 || getNationOrNull().getLevelNumber() >= requiredNationLevelForRank)
+					out.add(rank);
+			}
+			// Return out modified list of ranks, so that the player will not lose ranks
+			// they've been assigned when their nation goes down in a level temporarily. This
+			// ensures they save and load their proper list of ranks.
+			return Collections.unmodifiableList(out);
+		}
+		return Collections.unmodifiableList(nationRanks);
+	}
+
+	@ApiStatus.Internal
+	public List<String> getNationRanksForSaving() {
 		return Collections.unmodifiableList(nationRanks);
 	}