PlotSquared/Bukkit/src/main/java/com/plotsquared/bukkit/chat/Reflection.java

package com.plotsquared.bukkit.chat;

import org.bukkit.Bukkit;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * A class containing static utility methods and caches which are intended as reflective conveniences.
 * Unless otherwise noted, upon failure methods will return {@code null}.
 */
public final class Reflection {

	/**
	 * Stores loaded classes from the {@code net.minecraft.server} package.
	 */
	private static final Map<String, Class<?>> _loadedNMSClasses = new HashMap<String, Class<?>>();
	/**
	 * Stores loaded classes from the {@code org.bukkit.craftbukkit} package (and subpackages).
	 */
	private static final Map<String, Class<?>> _loadedOBCClasses = new HashMap<String, Class<?>>();
	private static final Map<Class<?>, Map<String, Field>> _loadedFields = new HashMap<Class<?>, Map<String, Field>>();
	/**
	 * Contains loaded methods in a cache.
	 * The map maps [types to maps of [method names to maps of [parameter types to method instances]]].
	 */
	private static final Map<Class<?>, Map<String, Map<ArrayWrapper<Class<?>>, Method>>> _loadedMethods = new HashMap<Class<?>, Map<String, Map<ArrayWrapper<Class<?>>, Method>>>();
	private static String _versionString;

	private Reflection() { }

	/**
	 * Gets the version string from the package name of the CraftBukkit server implementation.
	 * This is needed to bypass the JAR package name changing on each update.
	 *
	 * @return The version string of the OBC and NMS packages, <em>including the trailing dot</em>.
	 */
	public synchronized static String getVersion() {
		if (_versionString == null) {
			if (Bukkit.getServer() == null) {
				// The server hasn't started, static initializer call?
				return null;
			}
			String name = Bukkit.getServer().getClass().getPackage().getName();
			_versionString = name.substring(name.lastIndexOf('.') + 1) + ".";
		}

		return _versionString;
	}

	/**
	 * Gets a {@link Class} object representing a type contained within the {@code net.minecraft.server} versioned package.
	 * The class instances returned by this method are cached, such that no lookup will be done twice (unless multiple threads are accessing this method simultaneously).
	 *
	 * @param className The name of the class, excluding the package, within NMS.
	 * @return The class instance representing the specified NMS class, or {@code null} if it could not be loaded.
	 */
	public synchronized static Class<?> getNMSClass(String className) {
		if (_loadedNMSClasses.containsKey(className)) {
			return _loadedNMSClasses.get(className);
		}

		String fullName = "net.minecraft.server." + getVersion() + className;
		Class<?> clazz = null;
		try {
			clazz = Class.forName(fullName);
		} catch (Exception e) {
			_loadedNMSClasses.put(className, null);
			throw new RuntimeException(e);
		}
		_loadedNMSClasses.put(className, clazz);
		return clazz;
	}

	/**
	 * Gets a {@link Class} object representing a type contained within the {@code org.bukkit.craftbukkit} versioned package.
	 * The class instances returned by this method are cached, such that no lookup will be done twice (unless multiple threads are accessing this method simultaneously).
	 *
	 * @param className The name of the class, excluding the package, within OBC. This name may contain a subpackage name, such as {@code inventory.CraftItemStack}.
	 * @return The class instance representing the specified OBC class, or {@code null} if it could not be loaded.
	 */
	public synchronized static Class<?> getOBCClass(String className) {
		if (_loadedOBCClasses.containsKey(className)) {
			return _loadedOBCClasses.get(className);
		}

		String fullName = "org.bukkit.craftbukkit." + getVersion() + className;
		Class<?> clazz = null;
		try {
			clazz = Class.forName(fullName);
		} catch (Exception e) {
			_loadedOBCClasses.put(className, null);
			throw new RuntimeException(e);
		}
		_loadedOBCClasses.put(className, clazz);
		return clazz;
	}

	/**
	 * Attempts to get the NMS handle of a CraftBukkit object.
	 * <p>
	 * The only match currently attempted by this method is a retrieval by using a parameterless {@code getHandle()} method implemented by the runtime type of the specified object.
	 * </p>
	 *
	 * @param obj The object for which to retrieve an NMS handle.
	 * @return The NMS handle of the specified object, or {@code null} if it could not be retrieved using {@code getHandle()}.
	 */
	public synchronized static Object getHandle(Object obj) {
		try {
			return getMethod(obj.getClass(), "getHandle").invoke(obj);
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	/**
	 * Retrieves a {@link Field} instance declared by the specified class with the specified name.
	 * Java access modifiers are ignored during this retrieval. No guarantee is made as to whether the field
	 * returned will be an instance or static field.
	 * <p>
	 * A global caching mechanism within this class is used to store fields. Combined with synchronization, this guarantees that
	 * no field will be reflectively looked up twice.
	 * </p>
	 * <p>
	 * If a field is deemed suitable for return, {@link Field#setAccessible(boolean) setAccessible} will be invoked with an argument of {@code true} before it is returned.
	 * This ensures that callers do not have to check or worry about Java access modifiers when dealing with the returned instance.
	 * </p>
	 *
	 * @param clazz The class which contains the field to retrieve.
	 * @param name  The declared name of the field in the class.
	 * @return A field object with the specified name declared by the specified class.
	 * @see Class#getDeclaredField(String)
	 */
	public synchronized static Field getField(Class<?> clazz, String name) {
		Map<String, Field> loaded;
		if (!_loadedFields.containsKey(clazz)) {
			loaded = new HashMap<String, Field>();
			_loadedFields.put(clazz, loaded);
		} else {
			loaded = _loadedFields.get(clazz);
		}
		if (loaded.containsKey(name)) {
			// If the field is loaded (or cached as not existing), return the relevant value, which might be null
			return loaded.get(name);
		}
		try {
			Field field = clazz.getDeclaredField(name);
			field.setAccessible(true);
			loaded.put(name, field);
			return field;
		} catch (Exception e) {
			// Error loading
			e.printStackTrace();
			// Cache field as not existing
			loaded.put(name, null);
			return null;
		}
	}

	/**
	 * Retrieves a {@link Method} instance declared by the specified class with the specified name and argument types.
	 * Java access modifiers are ignored during this retrieval. No guarantee is made as to whether the field
	 * returned will be an instance or static field.
	 * <p>
	 * A global caching mechanism within this class is used to store method. Combined with synchronization, this guarantees that
	 * no method will be reflectively looked up twice.
	 * </p>
	 * <p>
	 * If a method is deemed suitable for return, {@link Method#setAccessible(boolean) setAccessible} will be invoked with an argument of {@code true} before it is returned.
	 * This ensures that callers do not have to check or worry about Java access modifiers when dealing with the returned instance.
	 * </p>
	 * <p>
	 * This method does <em>not</em> search superclasses of the specified type for methods with the specified signature.
	 * Callers wishing this behavior should use {@link Class#getDeclaredMethod(String, Class...)}.
	 *
	 * @param clazz The class which contains the method to retrieve.
	 * @param name  The declared name of the method in the class.
	 * @param args  The formal argument types of the method.
	 * @return A method object with the specified name declared by the specified class.
	 */
	public synchronized static Method getMethod(Class<?> clazz, String name, Class<?>... args) {
		if (!_loadedMethods.containsKey(clazz)) {
			_loadedMethods.put(clazz, new HashMap<String, Map<ArrayWrapper<Class<?>>, Method>>());
		}

		Map<String, Map<ArrayWrapper<Class<?>>, Method>> loadedMethodNames = _loadedMethods.get(clazz);
		if (!loadedMethodNames.containsKey(name)) {
			loadedMethodNames.put(name, new HashMap<ArrayWrapper<Class<?>>, Method>());
		}

		Map<ArrayWrapper<Class<?>>, Method> loadedSignatures = loadedMethodNames.get(name);
		ArrayWrapper<Class<?>> wrappedArg = new ArrayWrapper<Class<?>>(args);
		if (loadedSignatures.containsKey(wrappedArg)) {
			return loadedSignatures.get(wrappedArg);
		}

		for (Method m : clazz.getMethods()) {
  	  	  	if (m.getName().equals(name) && Arrays.equals(args, m.getParameterTypes())) {
  	  	  	  	m.setAccessible(true);
  	  	  	  	loadedSignatures.put(wrappedArg, m);
  	  	  	  	return m;
  	  	  	}
  	  	}
		loadedSignatures.put(wrappedArg, null);
		return null;
	}

}