Warn players every 5 minutes when their bank can't cover vehicle upkeep

src/main/java/net/tfminecraft/simplefactions/managers/FactionManager.java

@@ -482,6 +482,8 @@ public void time() {
 					leader.sendMessage("§cGet more prestige or unclaim provinces to counteract this!");
 				}
 			}
+			SimpleFactions.getInstance().getVehicleUpkeepService()
+					.warnBankShortfalls(Bukkit.getOnlinePlayers(), getSecondsUntilNewDay());
 		}
 		if (timer >= DAY_LENGTH_SECONDS) {
 			runDailyStep("player ledgers", () -> PlayerEconomyManager.get().clearAllDaily());

src/main/java/net/tfminecraft/simplefactions/vehicles/maintenance/VehicleMaintenanceMessages.java

@@ -1,5 +1,6 @@
 package net.tfminecraft.simplefactions.vehicles.maintenance;
 
+import net.tfminecraft.simplefactions.utils.Formatter;
 import net.tfminecraft.simplefactions.vehicles.maintenance.VehicleMaintenancePayService.PaymentSource;
 
 public final class VehicleMaintenanceMessages {
@@ -18,6 +19,15 @@ public static String payArmed(PaymentSource source) {
                 + (source == PaymentSource.BANK ? "bank" : "pouch") + ".";
     }
 
+    public static String bankShortfall(double shortfall, int secondsUntilCharge) {
+        // Round up so the final partial minute does not read as already due.
+        int minutes = (secondsUntilCharge + 59) / 60;
+        return "§cYou lack " + Formatter.formatMoney(shortfall)
+                + " denars in your personal bank to pay vehicle maintenance in "
+                + minutes / 60 + "h " + minutes % 60 + "m"
+                + " §7(/deco deposit for the bank, it does not count the pouch)";
+    }
+
     public static String paySuccess() {
         return "§aPaid vehicle maintenance.";
     }

src/main/java/net/tfminecraft/simplefactions/vehicles/maintenance/VehicleUpkeepService.java

@@ -4,6 +4,7 @@
 import net.tfminecraft.simplefactions.vehicles.maintenance.DenarEconomyPlayerBank.PlayerBank;
 import net.tfminecraft.simplefactions.vehicles.registry.PlayerVehicleRegistry;
 import net.tfminecraft.simplefactions.vehicles.registry.VehicleOwnershipQueries;
+import java.util.Collection;
 import java.util.UUID;
 
 import org.bukkit.Bukkit;
@@ -13,6 +14,7 @@
 import net.tfminecraft.simplefactions.SimpleFactions;
 import net.tfminecraft.simplefactions.player.PlayerEconomyManager;
 import net.tfminecraft.simplefactions.player.income.PlayerCashflow;
+import net.tfminecraft.simplefactions.utils.Formatter;
 import net.tfminecraft.vehicleframework.data.OwnedVehicleSummary;
 
 public final class VehicleUpkeepService {
@@ -63,6 +65,28 @@ public void processDailyUpkeep() {
         }
     }
 
+    /** Warns each player whose bank cannot cover their vehicle upkeep at the next new day. */
+    public void warnBankShortfalls(Collection<? extends Player> players, int secondsUntilCharge) {
+        if (secondsUntilCharge <= 0) {
+            return;
+        }
+        for (Player player : players) {
+            double upkeep = VehicleUpkeepProjection.projectedDailyUpkeep(player.getName(), registry);
+            if (upkeep <= 0.0) {
+                continue;
+            }
+            UUID playerUuid = playerBank.resolve(player.getName());
+            if (playerUuid == null) {
+                continue;
+            }
+            // Round to cents so a float residue never reads as "lack 0.00".
+            double shortfall = Formatter.formatDouble(upkeep - playerBank.getBankBalance(playerUuid));
+            if (shortfall > 0.0) {
+                player.sendMessage(VehicleMaintenanceMessages.bankShortfall(shortfall, secondsUntilCharge));
+            }
+        }
+    }
+
     public void tickHourlyDecay() {
         double fraction = VehiclesConfigLoader.getMaintenanceHourlyDamageFraction();
         double minHealth = VehiclesConfigLoader.getMaintenanceMinHealthFraction();

src/test/java/net/tfminecraft/simplefactions/vehicles/maintenance/VehicleUpkeepServiceTest.java

@@ -16,6 +16,8 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import java.io.IOException;
@@ -30,6 +32,7 @@
 import org.bukkit.Bukkit;
 import org.bukkit.OfflinePlayer;
 import org.bukkit.Server;
+import org.bukkit.entity.Player;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -168,6 +171,53 @@ void successfulUpkeepClearsExistingUnpaid() {
         assertFalse(store.isUnpaid("vehicle-1"));
     }
 
+    @Test
+    void warnsPlayerWhoseBankCannotCoverUpkeep() {
+        UUID playerUuid = UUID.randomUUID();
+        bank.setBalance(playerUuid, 5.0);
+        bank.remember("Alice", playerUuid);
+        VehicleOwnershipQueries.setSourceForTests(
+                new FakeOwnedInventory().add("vehicle-1", "ironclad", "player_Alice"));
+        Player alice = onlinePlayer("Alice", playerUuid);
+
+        service.warnBankShortfalls(List.of(alice), 3 * 3600 + 12 * 60);
+
+        verify(alice).sendMessage("§cYou lack 15.00 denars in your personal bank to pay vehicle maintenance"
+                + " in 3h 12m §7(/deco deposit for the bank, it does not count the pouch)");
+    }
+
+    @Test
+    void doesNotWarnWhenBankCoversUpkeep() {
+        UUID playerUuid = UUID.randomUUID();
+        bank.setBalance(playerUuid, 20.0);
+        bank.remember("Alice", playerUuid);
+        VehicleOwnershipQueries.setSourceForTests(
+                new FakeOwnedInventory().add("vehicle-1", "ironclad", "player_Alice"));
+        Player alice = onlinePlayer("Alice", playerUuid);
+
+        service.warnBankShortfalls(List.of(alice), 600);
+
+        verify(alice, never()).sendMessage(org.mockito.ArgumentMatchers.anyString());
+    }
+
+    @Test
+    void doesNotWarnPlayersWithoutVehicles() {
+        UUID playerUuid = UUID.randomUUID();
+        bank.remember("Alice", playerUuid);
+        Player alice = onlinePlayer("Alice", playerUuid);
+
+        service.warnBankShortfalls(List.of(alice), 600);
+
+        verify(alice, never()).sendMessage(org.mockito.ArgumentMatchers.anyString());
+    }
+
+    private static Player onlinePlayer(String name, UUID uuid) {
+        Player player = mock(Player.class);
+        when(player.getName()).thenReturn(name);
+        when(player.getUniqueId()).thenReturn(uuid);
+        return player;
+    }
+
     @Test
     void hourlyDecayDamagesUnpaidVehicles() {
         store.markUnpaid("vehicle-1", 1L);