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/*
 * Copyright 2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.codehaus.groovy.reflection;

import java.lang.reflect.Method;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import java.util.Collections;

/**
 * This class contains utility methods to determine which class called the
 * current class to multiple levels of depth.  Calls used to handle the
 * groovy MOP are excluded from the level counting.
 */
public class ReflectionUtils {

    // these are packages in the call stack that are only part of the groovy MOP
    private static final Set IGNORED_PACKAGES = new HashSet();

    static {
        //IGNORED_PACKAGES.add("java.lang.reflect");
        IGNORED_PACKAGES.add("groovy.lang");
        IGNORED_PACKAGES.add("org.codehaus.groovy.reflection");
        IGNORED_PACKAGES.add("org.codehaus.groovy.runtime.callsite");
        IGNORED_PACKAGES.add("org.codehaus.groovy.runtime.metaclass");
        IGNORED_PACKAGES.add("org.codehaus.groovy.runtime");
        IGNORED_PACKAGES.add("sun.reflect");
        IGNORED_PACKAGES.add("java.lang.invoke");
        IGNORED_PACKAGES.add("org.codehaus.groovy.vmplugin.v7");
    }

    private static final Method MAGIC_METHOD;

    static {
        Method meth;
        try {
            Class srr = Class.forName("sun.reflect.Reflection");
            meth = srr.getMethod("getCallerClass", Integer.TYPE);
        } catch (Throwable t) {
            meth = null;
        }
        MAGIC_METHOD = meth;
    }

    /**
     * Determine whether or not the getCallingClass methods will return
     * any sensible results.  On JVMs that are not Sun derived i.e.
     * (gcj, Harmony) this will likely return false.  When not available
     * all getCallingClass methods will return null.
     *
     * @return true if getCallingClass can return anything but null, false if
     *         it will only return null.
     */
    public static boolean isCallingClassReflectionAvailable() {
        return MAGIC_METHOD != null;
    }

    /**
     * Get the immediate calling class, ignoring MOP frames.
     *
     * @return The Class of the caller
     */
    public static Class getCallingClass() {
        return getCallingClass(1);
    }

    /**
     * Get the called that is matchLevel stack frames before the call,
     * ignoring MOP frames.
     *
     * @param matchLevel how may call stacks down to look.
     *                   If it is less than 1 it is treated as though it was 1.
     * @return The Class of the matched caller, or null if there aren't
     *         enough stackframes to satisfy matchLevel
     */
    public static Class getCallingClass(int matchLevel) {
        return getCallingClass(matchLevel, Collections.EMPTY_SET);
    }

    /**
     * Get the called that is matchLevel stack frames before the call,
     * ignoring MOP frames and desired exclude packages.
     *
     * @param matchLevel           how may call stacks down to look.
     *                             If it is less than 1 it is treated as though it was 1.
     * @param extraIgnoredPackages A collection of string names of packages to exclude
     *                             in addition to the MOP packages when counting stack frames.
     * @return The Class of the matched caller, or null if there aren't
     *         enough stackframes to satisfy matchLevel
     */
    public static Class getCallingClass(int matchLevel, Collection extraIgnoredPackages) {
        if (MAGIC_METHOD == null) {
            return null;
        }
        int depth = 0;
        try {
            Class c;
            // this super class stuff is for Java 1.4 support only
            // it isn't needed on a 5.0 VM
            Class sc;
            do {
                do {
                    c = (Class) MAGIC_METHOD.invoke(null, depth++);
                    if (c != null) {
                        sc = c.getSuperclass();
                    } else {
                        sc = null;
                    }
                } while (classShouldBeIgnored(c, extraIgnoredPackages)
                        || superClassShouldBeIgnored(sc));
            } while (c != null && matchLevel-- > 0);
            return c;
        } catch (Throwable t) {
            return null;
        }
    }

    private static boolean superClassShouldBeIgnored(Class sc) {
        return ((sc != null) && (sc.getPackage() != null) && "org.codehaus.groovy.runtime.callsite".equals(sc.getPackage().getName()));
    }

    private static boolean classShouldBeIgnored(Class c, Collection extraIgnoredPackages) {
        return ((c != null)
                && (c.isSynthetic()
                    || (c.getPackage() != null
                        && (IGNORED_PACKAGES.contains(c.getPackage().getName())
                          || extraIgnoredPackages.contains(c.getPackage().getName())))));
    }
}