Paper/paper-api/src/main/java/org/bukkit/GameRule.java

package org.bukkit;

import com.google.common.base.Preconditions;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.HashMap;
import java.util.Map;

/**
 * GameRules dictate certain behavior within Minecraft itself
 * <br>
 * For more information please visit the
 * <a href="https://minecraft.gamepedia.com/Commands/gamerule">Minecraft
 * Wiki</a>
 */
public final class GameRule<T> {

    private static Map<String, GameRule<?>> gameRules = new HashMap<>();
    // Boolean rules
    /**
     * Toggles the announcing of advancements.
     */
    public static final GameRule<Boolean> ANNOUNCE_ADVANCEMENTS = new GameRule<>("announceAdvancements", Boolean.class);

    /**
     * Whether command blocks should notify admins when they perform commands.
     */
    public static final GameRule<Boolean> COMMAND_BLOCK_OUTPUT = new GameRule<>("commandBlockOutput", Boolean.class);

    /**
     * Whether the server should skip checking player speed when the player is
     * wearing elytra.
     */
    public static final GameRule<Boolean> DISABLE_ELYTRA_MOVEMENT_CHECK = new GameRule<>("disableElytraMovementCheck", Boolean.class);

    /**
     * Whether time progresses from the current moment.
     */
    public static final GameRule<Boolean> DO_DAYLIGHT_CYCLE = new GameRule<>("doDaylightCycle", Boolean.class);

    /**
     * Whether entities that are not mobs should have drops.
     */
    public static final GameRule<Boolean> DO_ENTITY_DROPS = new GameRule<>("doEntityDrops", Boolean.class);

    /**
     * Whether fire should spread and naturally extinguish.
     */
    public static final GameRule<Boolean> DO_FIRE_TICK = new GameRule<>("doFireTick", Boolean.class);

    /**
     * Whether players should only be able to craft recipes they've unlocked
     * first.
     */
    public static final GameRule<Boolean> DO_LIMITED_CRAFTING = new GameRule<>("doLimitedCrafting", Boolean.class);

    /**
     * Whether mobs should drop items.
     */
    public static final GameRule<Boolean> DO_MOB_LOOT = new GameRule<>("doMobLoot", Boolean.class);

    /**
     * Whether mobs should naturally spawn.
     */
    public static final GameRule<Boolean> DO_MOB_SPAWNING = new GameRule<>("doMobSpawning", Boolean.class);

    /**
     * Whether blocks should have drops.
     */
    public static final GameRule<Boolean> DO_TILE_DROPS = new GameRule<>("doTileDrops", Boolean.class);

    /**
     * Whether the weather will change from the current moment.
     */
    public static final GameRule<Boolean> DO_WEATHER_CYCLE = new GameRule<>("doWeatherCycle", Boolean.class);

    /**
     * Whether the player should keep items in their inventory after death.
     */
    public static final GameRule<Boolean> KEEP_INVENTORY = new GameRule<>("keepInventory", Boolean.class);

    /**
     * Whether to log admin commands to server log.
     */
    public static final GameRule<Boolean> LOG_ADMIN_COMMANDS = new GameRule<>("logAdminCommands", Boolean.class);

    /**
     * Whether mobs can pick up items or change blocks.
     */
    public static final GameRule<Boolean> MOB_GRIEFING = new GameRule<>("mobGriefing", Boolean.class);

    /**
     * Whether players can regenerate health naturally through their hunger bar.
     */
    public static final GameRule<Boolean> NATURAL_REGENERATION = new GameRule<>("naturalRegeneration", Boolean.class);

    /**
     * Whether the debug screen shows all or reduced information.
     */
    public static final GameRule<Boolean> REDUCED_DEBUG_INFO = new GameRule<>("reducedDebugInfo", Boolean.class);

    /**
     * Whether the feedback from commands executed by a player should show up in
     * chat. Also affects the default behavior of whether command blocks store
     * their output text.
     */
    public static final GameRule<Boolean> SEND_COMMAND_FEEDBACK = new GameRule<>("sendCommandFeedback", Boolean.class);

    /**
     * Whether a message appears in chat when a player dies.
     */
    public static final GameRule<Boolean> SHOW_DEATH_MESSAGES = new GameRule<>("showDeathMessages", Boolean.class);

    /**
     * Whether players in spectator mode can generate chunks.
     */
    public static final GameRule<Boolean> SPECTATORS_GENERATE_CHUNKS = new GameRule<>("spectatorsGenerateChunks", Boolean.class);

    // Numerical rules
    /**
     * How often a random block tick occurs (such as plant growth, leaf decay,
     * etc.) per chunk section per game tick. 0 will disable random ticks,
     * higher numbers will increase random ticks.
     */
    public static final GameRule<Integer> RANDOM_TICK_SPEED = new GameRule<>("randomTickSpeed", Integer.class);

    /**
     * The number of blocks outward from the world spawn coordinates that a
     * player will spawn in when first joining a server or when dying without a
     * spawnpoint.
     */
    public static final GameRule<Integer> SPAWN_RADIUS = new GameRule<>("spawnRadius", Integer.class);

    /**
     * The maximum number of other pushable entities a mob or player can push,
     * before taking suffocation damage.
     * <br>
     * Setting to 0 disables this rule.
     */
    public static final GameRule<Integer> MAX_ENTITY_CRAMMING = new GameRule<>("maxEntityCramming", Integer.class);

    /**
     * Determines the number at which the chain of command blocks act as a
     * "chain."
     * <br>
     * This is the maximum amount of command blocks that can be activated in a
     * single tick from a single chain.
     */
    public static final GameRule<Integer> MAX_COMMAND_CHAIN_LENGTH = new GameRule<>("maxCommandChainLength", Integer.class);

    // All GameRules instantiated above this for organizational purposes
    private final String name;
    private final Class<T> type;

    private GameRule(@NotNull String name, @NotNull Class<T> clazz) {
        Preconditions.checkNotNull(name, "GameRule name cannot be null");
        Preconditions.checkNotNull(clazz, "GameRule type cannot be null");
        Preconditions.checkArgument(clazz == Boolean.class || clazz == Integer.class, "Must be of type Boolean or Integer. Found %s ", clazz.getName());
        this.name = name;
        this.type = clazz;
        gameRules.put(name, this);
    }

    /**
     * Get the name of this GameRule.
     *
     * @return the name of this GameRule
     */
    @NotNull
    public String getName() {
        return name;
    }

    /**
     * Get the type of this rule.
     *
     * @return the rule type; Integer or Boolean
     */
    @NotNull
    public Class<T> getType() {
        return type;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof GameRule)) {
            return false;
        }
        GameRule<?> other = (GameRule<?>) obj;
        return this.getName().equals(other.getName()) && this.getType() == other.getType();
    }

    @Override
    public String toString() {
        return "GameRule{" + "key=" + name + ", type=" + type + '}';
    }

    /**
     * Get a {@link GameRule} by its name.
     *
     * @param rule the name of the GameRule
     * @return the {@link GameRule} or null if no GameRule matches the given
     * name
     */
    @Nullable
    public static GameRule<?> getByName(@NotNull String rule) {
        Preconditions.checkNotNull(rule, "Rule cannot be null");
        return gameRules.get(rule);
    }

    /**
     * Get an immutable collection of {@link GameRule}s.
     *
     * @return an immutable collection containing all registered GameRules.
     */
    @NotNull
    public static GameRule<?>[] values() {
        return gameRules.values().toArray(new GameRule<?>[gameRules.size()]);
    }
}