LevelsExample.java

public class LandsLevelRequirementsExample implements Listener {
    private boolean anyLandRequirement = false;
    private final me.angeschossen.lands.api.LandsIntegration api;

    public LandsLevelRequirementsExample(Plugin plugin) {
        this.api = me.angeschossen.lands.api.LandsIntegration.of(plugin);

        api.onLoad(() -> { // requirements must be registered before Lands enables

            // land level requirements
            @Nullable Map<Level, ConfigurationSection> landLevels = api.getLevelsHandler().getLandSection();
            if (landLevels != null) {
                for (Map.Entry<Level, ConfigurationSection> entry : landLevels.entrySet()) {

                    ConfigurationSection requirement = entry.getValue().getConfigurationSection("requirements.upgradeablehoppers.hoppers");
                    if (requirement != null) {
                        int value = Math.max(requirement.getInt("required", 0), 0);

                        String reqName = StringUtils.colorize(requirement.getString("title", "Requirement Name"));
                        List<String> description = requirement.getStringList("description");
                        description.replaceAll(StringUtils::colorize);

                        entry.getKey().addRequirement(parseLandRequirement(reqName, description, value));
                        this.anyLandRequirement = true;
                    }
                }
            }
        });
    }


    private me.angeschossen.lands.api.levels.requirement.Requirement parseLandRequirement(@NotNull String reqName, @NotNull List<String> description, int value) {
        return new me.angeschossen.lands.api.levels.requirement.impl.Requirement(api, HolderType.LAND, "upgradeablehoppers_hoppers", reqName, description, value, String.valueOf(value)) {
            @Override
            public @NotNull String makeProgressDisplay(@NotNull MemberHolder memberHolder, float value) {
                return (int) value + "/" + (int) getRequired();
            }

            @Override
            public @NotNull CompletableFuture<Float> retrieveValue(@NotNull MemberHolder memberHolder) {
                return CompletableFuture.supplyAsync(() -> {
                    final Land land = (Land) memberHolder;
                    float hoppers = 0;

                    for (IHopperWorld world : UpgradeableHoppers.getInstance().getDatabase().getWorlds()) {
                        Container container = land.getContainer(world.getWorld());
                        if (container == null) {
                            continue; // land has no claims in this world
                        }

                        for (ChunkCoordinate chunkCoordinate : container.getChunks()) {
                            // get the amount of hoppers of a claimed chunk. Does NOT require hoppers to be loaded
                            hoppers += world.getHoppersAmountByChunk(new IChunkCoordinate(chunkCoordinate.getX(), chunkCoordinate.getZ()));
                        }
                    }

                    return hoppers;
                });
            }
        };
    }

    @Override
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(this, UpgradeableHoppers.getInstance());
    }

    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    public void onHopperBreak(HopperBreakEvent e) {
        handleHopperAmountMod(e.getHopper().getPosition(), -1);
    }

    @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
    public void onHopperPlace(HopperPlaceEvent e) {
        handleHopperAmountMod(e.getHopper().getPosition(), 1);
    }

    private void handleHopperAmountMod(@NotNull BlockPosition pos, int modify) {
        if (!this.anyLandRequirement) {
            return;
        }

        Land land = api.getLandByChunk(pos.getWorld(), pos.getChunkX(), pos.getChunkZ());
        if (land == null) {
            return; // location is wilderness
        }

        // add or remove from total amount in land
        land.modifyRequirementCache("upgradeablehoppers_hoppers", modify, false, true);
    }
}