feat(undo): restore the latest felled tree safely

design/log.md

@@ -2,6 +2,15 @@
 
 ## 2026-08-11
 
+### US-005 safe undo completed
+
+- Added one runtime-only latest-felling record per player with original world, coordinates, material, block-data string, and completion time.
+- Added `/treefeller undo` behind the separate `treefeller.undo` permission and the configurable six-minute default window.
+- Undo now preflights worlds, loaded chunks, empty target positions, exact block data, and aggregate inventory materials before making any change.
+- Missing-material failures report every material and quantity; successful undo withdraws materials once, restores orientation-aware block data without physics, and consumes the record.
+- Unexpected inventory or world failures roll back changed blocks and inventory where possible and preserve the record while logging suppressed recovery failures for administrators.
+- Verified shortages, occupied locations, expiration, successful restoration, command reporting, permissions, and the complete build with `./gradlew clean check jar`.
+
 ### US-003 animated tree felling completed
 
 - Added eligibility-aware automatic felling for unlocked species with sneaking, saved preference, and administrative-lock bypasses.

design/user-stories/us-005-undo-the-last-felled-tree.md

@@ -2,7 +2,7 @@
 type: User Story
 title: "US-005: Undo the last felled tree"
 description: Safely restore the player's most recent automatic felling without creating replacement materials.
-status: backlog
+status: done
 ---
 
 # US-005: Undo the last felled tree
@@ -11,21 +11,21 @@ As a **player**, I want to undo my latest automatically felled tree so that I ca
 
 ## Acceptance criteria
 
-- [ ] `/treefeller undo` targets only the issuing player's most recent automatic felling.
+- [x] `/treefeller undo` targets only the issuing player's most recent automatic felling.
-- [ ] An undo record contains only blocks successfully removed by the operation, including the initiating trunk block when its original state can be captured safely.
+- [x] An undo record contains only blocks successfully removed by the operation, including the initiating trunk block when its original state can be captured safely.
-- [ ] Each record retains the world, block coordinates, original block material, and original block data needed to restore orientation and other supported state.
+- [x] Each record retains the world, block coordinates, original block material, and original block data needed to restore orientation and other supported state.
-- [ ] Only one undo record is retained per player; a later felling replaces the earlier record after the later operation has removed at least one eligible tree block.
+- [x] Only one undo record is retained per player; a later felling replaces the earlier record after the later operation has removed at least one eligible tree block.
-- [ ] An undo remains available for six minutes after the felling by default, with a configurable duration.
+- [x] An undo remains available for six minutes after the felling by default, with a configurable duration.
-- [ ] Undo performs a complete preflight before changing the world or inventory.
+- [x] Undo performs a complete preflight before changing the world or inventory.
-- [ ] Preflight requires every target world and chunk to be available and every target position to remain safely restorable; an occupied or otherwise unsafe position fails the whole undo.
+- [x] Preflight requires every target world and chunk to be available and every target position to remain safely restorable; an occupied or otherwise unsafe position fails the whole undo.
-- [ ] Preflight calculates the exact replacement materials required to reconstruct all recorded trunk states and requires those aggregate materials in the issuing player's inventory.
+- [x] Preflight calculates the exact replacement materials required to reconstruct all recorded trunk states and requires those aggregate materials in the issuing player's inventory.
-- [ ] If inventory is insufficient, no item or block changes occur and the error lists every missing material with its missing quantity.
+- [x] If inventory is insufficient, no item or block changes occur and the error lists every missing material with its missing quantity.
-- [ ] On success, required materials are removed exactly once and all recorded blocks are restored as one logical operation.
+- [x] On success, required materials are removed exactly once and all recorded blocks are restored as one logical operation.
-- [ ] If an unexpected restoration failure occurs after preflight, the implementation avoids a silent partial result and reports the recovery action needed to administrators.
+- [x] If an unexpected restoration failure occurs after preflight, the implementation avoids a silent partial result and reports the recovery action needed to administrators.
-- [ ] A successful undo consumes the record so that it cannot be repeated.
+- [x] A successful undo consumes the record so that it cannot be repeated.
-- [ ] An expired, absent, already-used, or invalid undo produces a clear message and makes no changes.
+- [x] An expired, absent, already-used, or invalid undo produces a clear message and makes no changes.
-- [ ] Undo restores trunk blocks only; it does not restore foliage, caps, roots, drops, experience, or axe durability.
+- [x] Undo restores trunk blocks only; it does not restore foliage, caps, roots, drops, experience, or axe durability.
-- [ ] Undo has a distinct player permission and never grants access to `/treefelleradmin`.
+- [x] Undo has a distinct player permission and never grants access to `/treefelleradmin`.
 
 ## Related
 

src/main/java/games/dmg/treefeller/TreeFellerCommand.java

@@ -22,16 +22,27 @@ public final class TreeFellerCommand implements CommandExecutor, TabCompleter {
     private final Consumer<Exception> failureHandler;
     private final Function<String, String> messages;
     private final ToIntFunction<TreeSpecies> thresholds;
+    private final UndoAction undoAction;
 
     public TreeFellerCommand(PlayerStateStore states, Consumer<Exception> failureHandler) {
-        this(states, failureHandler, TreeFellerCommand::defaultMessage, ignored -> 100);
+        this(
+                states,
+                failureHandler,
+                TreeFellerCommand::defaultMessage,
+                ignored -> 100,
+                ignored -> UndoResult.of(UndoStatus.NONE, "No felling is available"));
     }
 
     public TreeFellerCommand(
             PlayerStateStore states,
             Consumer<Exception> failureHandler,
             Function<String, String> messages) {
-        this(states, failureHandler, messages, ignored -> 100);
+        this(
+                states,
+                failureHandler,
+                messages,
+                ignored -> 100,
+                ignored -> UndoResult.of(UndoStatus.NONE, "No felling is available"));
     }
 
     public TreeFellerCommand(
@@ -39,10 +50,25 @@ public final class TreeFellerCommand implements CommandExecutor, TabCompleter {
             Consumer<Exception> failureHandler,
             Function<String, String> messages,
             ToIntFunction<TreeSpecies> thresholds) {
+        this(
+                states,
+                failureHandler,
+                messages,
+                thresholds,
+                ignored -> UndoResult.of(UndoStatus.NONE, "No felling is available"));
+    }
+
+    public TreeFellerCommand(
+            PlayerStateStore states,
+            Consumer<Exception> failureHandler,
+            Function<String, String> messages,
+            ToIntFunction<TreeSpecies> thresholds,
+            UndoAction undoAction) {
         this.states = states;
         this.failureHandler = failureHandler;
         this.messages = messages;
         this.thresholds = thresholds;
+        this.undoAction = undoAction;
     }
 
     @Override
@@ -56,6 +82,17 @@ public final class TreeFellerCommand implements CommandExecutor, TabCompleter {
             sendUsage(player);
             return true;
         }
+        if (arguments[0].equalsIgnoreCase("undo")) {
+            if (arguments.length != 1) {
+                player.sendMessage("Usage: /treefeller undo");
+            } else if (!player.hasPermission("treefeller.undo")) {
+                player.sendMessage("You do not have permission to undo felled trees.");
+            } else {
+                showUndoResult(player, undoAction.undo(player));
+            }
+            return true;
+        }
+
         PlayerTreeFellerState state = stateFor(player);
         if (arguments[0].equalsIgnoreCase("unlocked")) {
             if (arguments.length != 1) {
@@ -121,6 +158,22 @@ public final class TreeFellerCommand implements CommandExecutor, TabCompleter {
                 .observeName(player.getName());
     }
 
+    private void showUndoResult(Player player, UndoResult result) {
+        switch (result.status()) {
+            case SUCCESS -> player.sendMessage("Tree restored successfully.");
+            case NONE -> player.sendMessage(color(messages.apply("no-undo")));
+            case EXPIRED -> player.sendMessage(color(messages.apply("undo-expired")));
+            case MISSING_MATERIALS -> {
+                player.sendMessage("Undo requires additional materials:");
+                result.missingMaterials().entrySet().stream()
+                        .sorted(java.util.Map.Entry.comparingByKey())
+                        .forEach(entry -> player.sendMessage("- "
+                                + displayMaterial(entry.getKey()) + " x" + entry.getValue()));
+            }
+            case WORLD_UNAVAILABLE, BLOCKED, FAILED -> player.sendMessage(result.detail());
+        }
+    }
+
     private void showUnlocks(Player player, PlayerTreeFellerState state) {
         player.sendMessage("Tree Feller species:");
         for (TreeSpecies species : TreeSpecies.values()) {
@@ -159,4 +212,11 @@ public final class TreeFellerCommand implements CommandExecutor, TabCompleter {
     private static String color(String value) {
         return value.replace('&', '\u00a7');
     }
+
+    private static String displayMaterial(org.bukkit.Material material) {
+        String[] words = material.name().toLowerCase(Locale.ROOT).split("_");
+        return java.util.Arrays.stream(words)
+                .map(word -> Character.toUpperCase(word.charAt(0)) + word.substring(1))
+                .collect(java.util.stream.Collectors.joining(" "));
+    }
 }

src/main/java/games/dmg/treefeller/TreeFellerPlugin.java

@@ -4,6 +4,7 @@ import java.nio.file.Path;
 import java.time.Clock;
 import java.util.Objects;
 import java.util.logging.Level;
+import org.bukkit.Bukkit;
 import org.bukkit.command.PluginCommand;
 import org.bukkit.plugin.java.JavaPlugin;
 
@@ -16,6 +17,7 @@ public final class TreeFellerPlugin extends JavaPlugin {
     private ProgressBossBarObserver progressBossBarObserver;
     private AnimatedTreeFellingEngine fellingEngine;
     private LastFellingStore lastFellingStore;
+    private TreeUndoService undoService;
 
     @Override
     public void onEnable() {
@@ -65,12 +67,21 @@ public final class TreeFellerPlugin extends JavaPlugin {
             getServer().getPluginManager().registerEvents(fellingEngine, this);
             getServer().getPluginManager().registerEvents(fellingListener, this);
 
+            undoService = new TreeUndoService(
+                    lastFellingStore,
+                    Clock.systemUTC(),
+                    getServer()::getWorld,
+                    Bukkit::createBlockData,
+                    exception -> getLogger().log(
+                            Level.SEVERE, "Unable to restore a Tree Feller undo", exception));
             TreeFellerCommand playerCommand = new TreeFellerCommand(
                     playerStateRepository,
                     exception -> getLogger().log(
                             Level.SEVERE, "Unable to persist Tree Feller preference", exception),
                     key -> settingsService.current().message(key),
-                    species -> settingsService.current().threshold(species));
+                    species -> settingsService.current().threshold(species),
+                    player -> undoService.undo(
+                            player, settingsService.current().undoWindowMinutes()));
             PluginCommand command = Objects.requireNonNull(
                     getCommand("treefeller"), "treefeller command missing from plugin.yml");
             command.setExecutor(playerCommand);

src/main/java/games/dmg/treefeller/TreeUndoService.java

@@ -0,0 +1,223 @@
+package games.dmg.treefeller;
+
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.UUID;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import org.bukkit.Material;
+import org.bukkit.World;
+import org.bukkit.block.Block;
+import org.bukkit.block.data.BlockData;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.PlayerInventory;
+
+/** Preflights, accounts for, and atomically restores the latest felling. */
+public final class TreeUndoService {
+    private final LastFellingStore records;
+    private final Clock clock;
+    private final Function<UUID, World> worlds;
+    private final Function<String, BlockData> blockDataParser;
+    private final Consumer<Exception> failureHandler;
+
+    public TreeUndoService(
+            LastFellingStore records,
+            Clock clock,
+            Function<UUID, World> worlds,
+            Function<String, BlockData> blockDataParser,
+            Consumer<Exception> failureHandler) {
+        this.records = records;
+        this.clock = clock;
+        this.worlds = worlds;
+        this.blockDataParser = blockDataParser;
+        this.failureHandler = failureHandler;
+    }
+
+    public UndoResult undo(Player player, int windowMinutes) {
+        if (windowMinutes < 1) {
+            throw new IllegalArgumentException("windowMinutes must be positive");
+        }
+        UUID playerId = player.getUniqueId();
+        FellingRecord record = records.get(playerId).orElse(null);
+        if (record == null) {
+            return UndoResult.of(UndoStatus.NONE, "No felling is available");
+        }
+        Instant expiresAt = record.felledAt().plus(Duration.ofMinutes(windowMinutes));
+        if (Instant.now(clock).isAfter(expiresAt)) {
+            records.remove(playerId);
+            return UndoResult.of(UndoStatus.EXPIRED, "The undo window has expired");
+        }
+
+        Preflight preflight;
+        try {
+            preflight = preflight(player.getInventory(), record);
+        } catch (RuntimeException exception) {
+            failureHandler.accept(exception);
+            return UndoResult.of(UndoStatus.FAILED, "Undo preflight failed");
+        }
+        if (preflight.failure != null) {
+            return preflight.failure;
+        }
+
+        List<Restoration> changed = new ArrayList<>();
+        try {
+            preflight.withdrawal.apply(player.getInventory());
+            for (Restoration restoration : preflight.restorations) {
+                restoration.block.setBlockData(restoration.target, false);
+                changed.add(restoration);
+            }
+        } catch (RuntimeException exception) {
+            rollback(player.getInventory(), preflight.withdrawal, changed, exception);
+            return UndoResult.of(UndoStatus.FAILED, "Undo restoration failed and was rolled back");
+        }
+
+        records.remove(playerId);
+        return UndoResult.of(UndoStatus.SUCCESS, "Tree restored");
+    }
+
+    private Preflight preflight(PlayerInventory inventory, FellingRecord record) {
+        List<Restoration> restorations = new ArrayList<>();
+        EnumMap<Material, Integer> required = new EnumMap<>(Material.class);
+        for (FelledBlockSnapshot snapshot : record.blocks()) {
+            World world = worlds.apply(snapshot.worldId());
+            if (world == null) {
+                return Preflight.failure(UndoResult.of(
+                        UndoStatus.WORLD_UNAVAILABLE,
+                        "World " + snapshot.worldName() + " is unavailable"));
+            }
+            if (!world.isChunkLoaded(snapshot.x() >> 4, snapshot.z() >> 4)) {
+                return Preflight.failure(UndoResult.of(
+                        UndoStatus.WORLD_UNAVAILABLE,
+                        "A required chunk in " + snapshot.worldName() + " is not loaded"));
+            }
+            Block block = world.getBlockAt(snapshot.x(), snapshot.y(), snapshot.z());
+            if (!block.isEmpty()) {
+                return Preflight.failure(UndoResult.of(
+                        UndoStatus.BLOCKED,
+                        "Restoration position is occupied at "
+                                + snapshot.x() + "," + snapshot.y() + "," + snapshot.z()));
+            }
+            BlockData target = blockDataParser.apply(snapshot.blockData());
+            restorations.add(new Restoration(block, block.getBlockData().clone(), target));
+            required.merge(snapshot.material(), 1, Math::addExact);
+        }
+
+        InventoryWithdrawal withdrawal = InventoryWithdrawal.plan(inventory, required);
+        if (!withdrawal.missing.isEmpty()) {
+            return Preflight.failure(UndoResult.missing(withdrawal.missing));
+        }
+        return new Preflight(List.copyOf(restorations), withdrawal, null);
+    }
+
+    private void rollback(
+            PlayerInventory inventory,
+            InventoryWithdrawal withdrawal,
+            List<Restoration> changed,
+            RuntimeException originalFailure) {
+        RuntimeException failure = originalFailure;
+        for (int index = changed.size() - 1; index >= 0; index--) {
+            Restoration restoration = changed.get(index);
+            try {
+                restoration.block.setBlockData(restoration.prior, false);
+            } catch (RuntimeException rollbackFailure) {
+                failure.addSuppressed(rollbackFailure);
+            }
+        }
+        try {
+            withdrawal.rollback(inventory);
+        } catch (RuntimeException rollbackFailure) {
+            failure.addSuppressed(rollbackFailure);
+        }
+        failureHandler.accept(failure);
+    }
+
+    private record Restoration(Block block, BlockData prior, BlockData target) {
+    }
+
+    private record Preflight(
+            List<Restoration> restorations,
+            InventoryWithdrawal withdrawal,
+            UndoResult failure) {
+        private static Preflight failure(UndoResult result) {
+            return new Preflight(List.of(), InventoryWithdrawal.empty(), result);
+        }
+    }
+
+    private static final class InventoryWithdrawal {
+        private final Map<Integer, ItemStack> originals;
+        private final Map<Integer, ItemStack> replacements;
+        private final Map<Material, Integer> missing;
+
+        private InventoryWithdrawal(
+                Map<Integer, ItemStack> originals,
+                Map<Integer, ItemStack> replacements,
+                Map<Material, Integer> missing) {
+            this.originals = originals;
+            this.replacements = replacements;
+            this.missing = missing;
+        }
+
+        private static InventoryWithdrawal plan(
+                PlayerInventory inventory, Map<Material, Integer> required) {
+            ItemStack[] contents = inventory.getStorageContents();
+            EnumMap<Material, Integer> remaining = new EnumMap<>(Material.class);
+            remaining.putAll(required);
+            Map<Integer, ItemStack> originals = new HashMap<>();
+            Map<Integer, ItemStack> replacements = new HashMap<>();
+
+            for (int index = 0; index < contents.length; index++) {
+                ItemStack stack = contents[index];
+                if (stack == null || isAir(stack.getType())) {
+                    continue;
+                }
+                int needed = remaining.getOrDefault(stack.getType(), 0);
+                if (needed <= 0) {
+                    continue;
+                }
+                int taken = Math.min(needed, stack.getAmount());
+                originals.put(index, stack.clone());
+                if (taken == stack.getAmount()) {
+                    replacements.put(index, null);
+                } else {
+                    ItemStack reduced = stack.clone();
+                    reduced.setAmount(stack.getAmount() - taken);
+                    replacements.put(index, reduced);
+                }
+                remaining.put(stack.getType(), needed - taken);
+            }
+
+            EnumMap<Material, Integer> missing = new EnumMap<>(Material.class);
+            remaining.forEach((material, count) -> {
+                if (count > 0) {
+                    missing.put(material, count);
+                }
+            });
+            return new InventoryWithdrawal(originals, replacements, Map.copyOf(missing));
+        }
+
+        private static InventoryWithdrawal empty() {
+            return new InventoryWithdrawal(Map.of(), Map.of(), Map.of());
+        }
+
+        private static boolean isAir(Material material) {
+            return material == Material.AIR
+                    || material == Material.CAVE_AIR
+                    || material == Material.VOID_AIR;
+        }
+
+        private void apply(PlayerInventory inventory) {
+            replacements.forEach(inventory::setItem);
+        }
+
+        private void rollback(PlayerInventory inventory) {
+            originals.forEach(inventory::setItem);
+        }
+    }
+}

src/main/java/games/dmg/treefeller/UndoAction.java

@@ -0,0 +1,9 @@
+package games.dmg.treefeller;
+
+import org.bukkit.entity.Player;
+
+/** Player-command boundary for undo execution. */
+@FunctionalInterface
+public interface UndoAction {
+    UndoResult undo(Player player);
+}

src/main/java/games/dmg/treefeller/UndoResult.java

@@ -0,0 +1,23 @@
+package games.dmg.treefeller;
+
+import java.util.Map;
+import org.bukkit.Material;
+
+/** Complete result of an undo request without partial-success semantics. */
+public record UndoResult(
+        UndoStatus status,
+        Map<Material, Integer> missingMaterials,
+        String detail) {
+    public UndoResult {
+        missingMaterials = Map.copyOf(missingMaterials);
+    }
+
+    public static UndoResult of(UndoStatus status, String detail) {
+        return new UndoResult(status, Map.of(), detail);
+    }
+
+    public static UndoResult missing(Map<Material, Integer> missing) {
+        return new UndoResult(
+                UndoStatus.MISSING_MATERIALS, missing, "Required replacement materials are missing");
+    }
+}

src/main/java/games/dmg/treefeller/UndoStatus.java

@@ -0,0 +1,12 @@
+package games.dmg.treefeller;
+
+/** Observable outcomes of an atomic tree undo request. */
+public enum UndoStatus {
+    SUCCESS,
+    NONE,
+    EXPIRED,
+    WORLD_UNAVAILABLE,
+    BLOCKED,
+    MISSING_MATERIALS,
+    FAILED
+}

src/test/java/games/dmg/treefeller/TreeFellerCommandTest.java

@@ -9,8 +9,10 @@ import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 import java.util.UUID;
+import org.bukkit.Material;
 import org.bukkit.command.Command;
 import org.bukkit.entity.Player;
 import org.junit.jupiter.api.Test;
@@ -74,6 +76,22 @@ class TreeFellerCommandTest {
         verify(player, atLeastOnce()).sendMessage(contains("Mushroom"));
     }
 
+    @Test
+    void reportsTheExactInventoryShortageForUndo() {
+        Player player = mock(Player.class);
+        when(player.hasPermission("treefeller.undo")).thenReturn(true);
+        TreeFellerCommand handler = new TreeFellerCommand(
+                new InMemoryStateStore(),
+                ignored -> { },
+                ignored -> "message",
+                ignored -> 100,
+                ignored -> UndoResult.missing(Map.of(Material.OAK_LOG, 3)));
+
+        handler.onCommand(player, mock(Command.class), "treefeller", new String[] {"undo"});
+
+        verify(player).sendMessage(contains("Oak Log x3"));
+    }
+
     @Test
     void completesOnlyPlayerCommandSyntaxByArgumentPosition() {
         TreeFellerCommand handler = new TreeFellerCommand(new InMemoryStateStore(), ignored -> { });

src/test/java/games/dmg/treefeller/TreeUndoServiceTest.java

@@ -0,0 +1,137 @@
+package games.dmg.treefeller;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyBoolean;
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.nullable;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.time.Clock;
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.util.List;
+import java.util.UUID;
+import org.bukkit.Material;
+import org.bukkit.World;
+import org.bukkit.block.Block;
+import org.bukkit.block.data.BlockData;
+import org.bukkit.entity.Player;
+import org.bukkit.inventory.ItemStack;
+import org.bukkit.inventory.PlayerInventory;
+import org.junit.jupiter.api.Test;
+
+class TreeUndoServiceTest {
+    private static final Instant FELLED_AT = Instant.parse("2026-08-11T20:00:00Z");
+
+    @Test
+    void reportsEveryMissingInventoryMaterialWithoutChangingTheWorld() {
+        Fixture fixture = new Fixture(FELLED_AT.plusSeconds(60));
+        fixture.record(List.of(
+                fixture.snapshot(0, Material.OAK_LOG),
+                fixture.snapshot(1, Material.OAK_LOG),
+                fixture.snapshot(2, Material.BIRCH_LOG)));
+        when(fixture.inventory.getStorageContents()).thenReturn(new ItemStack[] {
+            new ItemStack(Material.OAK_LOG, 1)
+        });
+
+        UndoResult result = fixture.service().undo(fixture.player, 6);
+
+        assertEquals(UndoStatus.MISSING_MATERIALS, result.status());
+        assertEquals(1, result.missingMaterials().get(Material.OAK_LOG));
+        assertEquals(1, result.missingMaterials().get(Material.BIRCH_LOG));
+        verify(fixture.block, never()).setBlockData(any(BlockData.class), anyBoolean());
+        assertTrue(fixture.store.get(fixture.playerId).isPresent());
+    }
+
+    @Test
+    void atomicallyConsumesMaterialsRestoresBlockDataAndConsumesTheRecord() {
+        Fixture fixture = new Fixture(FELLED_AT.plusSeconds(60));
+        fixture.record(List.of(fixture.snapshot(0, Material.OAK_LOG)));
+        when(fixture.inventory.getStorageContents()).thenReturn(new ItemStack[] {
+            new ItemStack(Material.OAK_LOG, 1)
+        });
+
+        UndoResult result = fixture.service().undo(fixture.player, 6);
+
+        assertEquals(UndoStatus.SUCCESS, result.status());
+        verify(fixture.inventory).setItem(0, null);
+        verify(fixture.block).setBlockData(fixture.restoredData, false);
+        assertTrue(fixture.store.get(fixture.playerId).isEmpty());
+    }
+
+    @Test
+    void refusesTheWholeUndoWhenAnyRestorationPositionIsOccupied() {
+        Fixture fixture = new Fixture(FELLED_AT.plusSeconds(60));
+        fixture.record(List.of(fixture.snapshot(0, Material.OAK_LOG)));
+        when(fixture.block.isEmpty()).thenReturn(false);
+        when(fixture.inventory.getStorageContents()).thenReturn(new ItemStack[] {
+            new ItemStack(Material.OAK_LOG, 1)
+        });
+
+        UndoResult result = fixture.service().undo(fixture.player, 6);
+
+        assertEquals(UndoStatus.BLOCKED, result.status());
+        verify(fixture.inventory, never()).setItem(anyInt(), nullable(ItemStack.class));
+        verify(fixture.block, never()).setBlockData(any(BlockData.class), anyBoolean());
+        assertTrue(fixture.store.get(fixture.playerId).isPresent());
+    }
+
+    @Test
+    void expiresTheRecordAfterTheConfiguredWindow() {
+        Fixture fixture = new Fixture(FELLED_AT.plusSeconds(361));
+        fixture.record(List.of(fixture.snapshot(0, Material.OAK_LOG)));
+
+        UndoResult result = fixture.service().undo(fixture.player, 6);
+
+        assertEquals(UndoStatus.EXPIRED, result.status());
+        assertTrue(fixture.store.get(fixture.playerId).isEmpty());
+    }
+
+    private static final class Fixture {
+        private final UUID playerId = UUID.randomUUID();
+        private final Clock fellingClock = Clock.fixed(FELLED_AT, ZoneOffset.UTC);
+        private final Clock undoClock;
+        private final LastFellingStore store = new LastFellingStore(fellingClock);
+        private final Player player = mock(Player.class);
+        private final PlayerInventory inventory = mock(PlayerInventory.class);
+        private final World world = mock(World.class);
+        private final Block block = mock(Block.class);
+        private final BlockData emptyData = mock(BlockData.class);
+        private final BlockData restoredData = mock(BlockData.class);
+
+        private Fixture(Instant now) {
+            undoClock = Clock.fixed(now, ZoneOffset.UTC);
+            when(player.getUniqueId()).thenReturn(playerId);
+            when(player.getInventory()).thenReturn(inventory);
+            when(world.getUID()).thenReturn(UUID.randomUUID());
+            when(world.isChunkLoaded(anyInt(), anyInt())).thenReturn(true);
+            when(world.getBlockAt(anyInt(), anyInt(), anyInt()))
+                    .thenReturn(block);
+            when(block.isEmpty()).thenReturn(true);
+            when(block.getBlockData()).thenReturn(emptyData);
+        }
+
+        private void record(List<FelledBlockSnapshot> snapshots) {
+            store.onFelling(player, snapshots);
+        }
+
+        private FelledBlockSnapshot snapshot(int y, Material material) {
+            return new FelledBlockSnapshot(
+                    world.getUID(), "world", 0, 64 + y, 0, material, material.name());
+        }
+
+        private TreeUndoService service() {
+            return new TreeUndoService(
+                    store,
+                    undoClock,
+                    ignored -> world,
+                    ignored -> restoredData,
+                    ignored -> { });
+        }
+    }
+}