Adds multiple home support.

src/main/java/com/majinnaibu/bukkitplugins/metropolis/HomeNumberAllocator.java

@@ -0,0 +1,41 @@
+/*
+This file is part of Metropolis.
+
+Metropolis is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+Metropolis is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with Metropolis. If not, see <https://www.gnu.org/licenses/agpl-3.0.txt>.
+*/
+
+package com.majinnaibu.bukkitplugins.metropolis;
+
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+public final class HomeNumberAllocator {
+  private HomeNumberAllocator() {}
+
+  public static int nextHomeNumber(List<Plot> plots) {
+    Set<Integer> allocatedNumbers = new HashSet<>();
+    for (Plot plot : plots) {
+      if (plot instanceof PlayerHome home) {
+        allocatedNumbers.add(home.getNumber());
+      }
+    }
+
+    int nextHomeNumber = 1;
+    while (allocatedNumbers.contains(nextHomeNumber)) {
+      nextHomeNumber++;
+    }
+    return nextHomeNumber;
+  }
+}