Add first steps for gui

ic_plugin_core/src/main/java/nl/interestingcorner/core/db/DatabaseManager.java

@@ -60,6 +60,7 @@ public enum DatabaseManager {
 
     public void registerDatabaseInitializeListener(DatabaseInitializeListener listener) {
         this.databaseInitializeListeners.add(listener);
+        this.app.getLogger().log(Level.INFO, "Registered database initialize listener: {0}", listener.getClass().getName());
 
         // immediately initialize if the database is already initialized
         if (this.initialized) {

ic_plugin_core/src/main/java/nl/interestingcorner/core/gui/GUI.java

@@ -0,0 +1,14 @@
+package nl.interestingcorner.core.gui;
+
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryHolder;
+
+public class GUI implements InventoryHolder {
+
+    @Override
+    public Inventory getInventory() {
+        // TODO Auto-generated method stub
+        throw new UnsupportedOperationException("Unimplemented method 'getInventory'");
+    }
+    
+}

ic_plugin_core/src/main/java/nl/interestingcorner/core/gui/GUIBuilder.java

@@ -0,0 +1,42 @@
+package nl.interestingcorner.core.gui;
+
+import java.util.List;
+
+import org.bukkit.Bukkit;
+import org.bukkit.inventory.Inventory;
+import org.bukkit.inventory.InventoryHolder;
+import org.bukkit.inventory.ItemStack;
+
+public class GUIBuilder {
+    public static final int MAX_INVENTORY_SIZE = 54; // max size of inventory before pages are needed
+    public static final int MAX_PAGE_INVENTORY_SIZE = 45; // max amount of items on a page
+
+    public Inventory buildInventory(List<ItemStack> items) {
+        /**
+         * if more than 45, add pages. Split by 45 items per page.
+         * use bottom row leftmost and rightmost item for navigation.
+         * use paper item for page number display in middle.
+         * use lore of navigation items clicked to handle showing next/previous page.
+         * use player.getOpeninventory() to get current inventory and update or close
+         * it.
+         */
+
+        int itemsAmount = items.size();
+        int pagesAmount = getPagesAmount(itemsAmount);
+
+        Inventory gui = Bukkit.createInventory(null, MAX_INVENTORY_SIZE, "Coordinates Menu");
+
+        for (ItemStack item : items) {
+            gui.addItem(item);
+        }
+
+        return gui;
+    }
+
+    private static int getPagesAmount(int itemsAmount) {
+        if (itemsAmount > MAX_INVENTORY_SIZE) {
+            return ((itemsAmount / MAX_PAGE_INVENTORY_SIZE) + 1);
+        }
+        return 1;
+    }
+}