Adds %Level_[gamemode]_island_level_max% placeholder

This records the lifetime maximum level the island has ever had.
Addresses #271

src/main/java/world/bentobox/level/Level.java

@@ -228,6 +228,9 @@ public class Level extends Addon {
         getPlugin().getPlaceholdersManager().registerPlaceholder(this,
                 gm.getDescription().getName().toLowerCase() + "_points_to_next_level",
                 user -> getManager().getPointsToNextString(gm.getOverWorld(), user.getUniqueId()));
+        getPlugin().getPlaceholdersManager().registerPlaceholder(this,
+                gm.getDescription().getName().toLowerCase() + "_island_level_max",
+                user -> String.valueOf(getManager().getIslandMaxLevel(gm.getOverWorld(), user.getUniqueId())));
 
         // Visited Island Level
         getPlugin().getPlaceholdersManager().registerPlaceholder(this,

src/main/java/world/bentobox/level/LevelsManager.java

@@ -231,6 +231,19 @@ public class LevelsManager {
         return island == null ? 0L : getLevelsData(island).getLevel();
     }
 
+    /**
+     * Get the maximum level ever given to this island
+     * @param world - world where the island is
+     * @param targetPlayer - target player UUID
+     * @return Max level of the player's island or zero if player is unknown or UUID is null
+     */
+    public long getIslandMaxLevel(@NonNull World world, @Nullable UUID targetPlayer) {
+        if (targetPlayer == null) return 0L;
+        // Get the island
+        Island island = addon.getIslands().getIsland(world, targetPlayer);
+        return island == null ? 0L : getLevelsData(island).getMaxLevel();
+    }
+
     /**
      * Returns a formatted string of the target player's island level
      * @param world - world where the island is

src/main/java/world/bentobox/level/objects/IslandLevels.java

@@ -43,6 +43,11 @@ public class IslandLevels implements DataObject {
      */
     @Expose
     private long pointsToNextLevel;
+    /**
+     * The maximum level this island has ever had
+     */
+    @Expose
+    private long maxLevel;
 
     /**
      * Underwater count
@@ -94,6 +99,10 @@ public class IslandLevels implements DataObject {
      */
     public void setLevel(long level) {
         this.level = level;
+        // Track maximum level
+        if (level > this.maxLevel) {
+            maxLevel = level;
+        }
     }
 
     /**
@@ -124,6 +133,14 @@ public class IslandLevels implements DataObject {
         this.pointsToNextLevel = pointsToNextLevel;
     }
 
+    /**
+     * Get the maximum level ever set using {@link #setLevel(long)}
+     * @return the maxLevel
+     */
+    public long getMaxLevel() {
+        return maxLevel;
+    }
+
     /**
      * @return the uwCount
      */

src/test/java/world/bentobox/level/LevelsManagerTest.java

@@ -270,6 +270,15 @@ public class LevelsManagerTest {
         //Map<UUID, Long> tt = lm.getTopTen(world, 10);
         //assertEquals(1, tt.size());
         //assertTrue(tt.get(uuid) == 10000);
+        assertEquals(10000L, lm.getIslandMaxLevel(world, uuid));
+
+        results.setLevel(5000);
+        lm.calculateLevel(uuid, island);
+        // Complete the pipelined completable future
+        cf.complete(results);
+        assertEquals(5000L, lm.getLevelsData(island).getLevel());
+        // Still should be 10000
+        assertEquals(10000L, lm.getIslandMaxLevel(world, uuid));
 
     }