Improve configuration handling for worlds

(and fix bug with old configuration handling)

src/main/java/xyz/alicedtrh/happyday/HappyDay.java

@@ -1,6 +1,7 @@
 package xyz.alicedtrh.happyday;
 
 import org.bukkit.Bukkit;
+import org.bukkit.World;
 import org.bukkit.event.entity.CreatureSpawnEvent;
 import org.bukkit.plugin.java.JavaPlugin;
 import org.jetbrains.annotations.NotNull;
@@ -42,7 +43,7 @@ public static void setSuspended(boolean suspended) {
             monsterRemover.debouncer.stopAllTasks();
         } else {
             log().info("Players are online. Enabling plugin");
-            monsterRemover.schedule(Bukkit.getWorld(WORLD));
+            monsterRemover.schedule(WORLD);
         }
     }
 
@@ -58,22 +59,22 @@ public void onEnable() {
         }
 
         //Fail early if there's no valid world setup.
-        Objects.requireNonNull(Bukkit.getWorld(WORLD));
+        try {
+            Objects.requireNonNull(WORLD);
+        } catch (NullPointerException e) {
+            log().severe("Couldn't find a valid world! Make sure your configuration is correct.");
+            throw new InvalidWorldException("Couldn't find a valid world! Make sure your configuration is correct.", e);
+        }
+
 
         getServer().getPluginManager().registerEvents(new HappyDayEventHandler(), this);
 
         setSuspended(true);
     }
 
     private void setupConfiguration() {
-        File oldConfig = new File(getDataFolder() + "config.yml");
-        if(oldConfig.exists() && oldConfig.canWrite()) {
-            if(oldConfig.delete()) {
-                log().warning("Deleted old config file. Please make any changes in the new configuration file if needed.");
-            }
-        }
-
         ConfigManager config = ConfigManager.create(this);
+        config.addConverter(World.class, Bukkit::getWorld, World::getName);
         config.target(HappyDayConfig.class);
         config.saveDefaults();
         config.load();

src/main/java/xyz/alicedtrh/happyday/HappyDayConfig.java

@@ -1,5 +1,7 @@
 package xyz.alicedtrh.happyday;
 
+import org.bukkit.Bukkit;
+import org.bukkit.World;
 import org.bukkit.event.entity.CreatureSpawnEvent;
 import redempt.redlib.config.annotations.Comment;
 import redempt.redlib.config.annotations.ConfigMappable;
@@ -29,8 +31,8 @@ public class HappyDayConfig {
     @Comment("When false, disables the entire mod. (default: true)")
     public static boolean ENABLED = true;
 
-    @Comment("The world that HappyDay is active on. (Default: world)")
-    public static String WORLD = "world";
+    @Comment("The world that HappyDay is active on.")
+    public static World WORLD = Bukkit.getWorlds().get(0);
 
     @Comment("Times used internally by the mod to figure out when night and day are")
     @Comment("This is an advanced option, don't touch this unless you know what you're doing.")

src/main/java/xyz/alicedtrh/happyday/HappyDayEventHandler.java

@@ -18,12 +18,12 @@ public final class HappyDayEventHandler implements Listener {
 
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onTimeSkipEvent(TimeSkipEvent event) {
-        debouncer.debounce(() -> HappyDay.monsterRemover.schedule(Bukkit.getWorld(WORLD)), 20);
+        debouncer.debounce(() -> HappyDay.monsterRemover.schedule(WORLD), 20);
     }
 
     @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
     public void onPlayerQuitEvent(PlayerQuitEvent event) {
-        World world = Objects.requireNonNull(Bukkit.getWorld(WORLD));
+        World world = Objects.requireNonNull(WORLD);
         // The player hasn't quit at this point so the player-count should be 1 if this is the last person
         if(world.getPlayerCount() <= 1) {
             HappyDay.setSuspended(true);

src/main/java/xyz/alicedtrh/happyday/InvalidWorldException.java

@@ -0,0 +1,7 @@
+package xyz.alicedtrh.happyday;
+
+public class InvalidWorldException extends RuntimeException {
+    public InvalidWorldException(String msg, NullPointerException e) {
+        super(msg, e);
+    }
+}