/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.logging.log4j.core.util;

import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;

import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.status.StatusLogger;
import org.apache.logging.log4j.util.LoaderUtil;
import org.apache.logging.log4j.util.PropertiesUtil;

/**
 * Load resources (or images) from various sources.
 */
public final class Loader {

    private static final Logger LOGGER = StatusLogger.getLogger();

    private static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

    private Loader() {
    }

    /**
     * Returns the ClassLoader to use.
     * @return the ClassLoader.
     */
    public static ClassLoader getClassLoader() {
        return getClassLoader(Loader.class, null);
    }

    /**
     * Returns the ClassLoader of current thread if possible, or falls back to the system ClassLoader if none is
     * available.
     *
     * @return the TCCL.
     * @see org.apache.logging.log4j.util.LoaderUtil#getThreadContextClassLoader()
     */
    public static ClassLoader getThreadContextClassLoader() {
        return LoaderUtil.getThreadContextClassLoader();
    }

    // TODO: this method could use some explanation
    public static ClassLoader getClassLoader(final Class<?> class1, final Class<?> class2) {
        final ClassLoader threadContextClassLoader = getThreadContextClassLoader();
        final ClassLoader loader1 = class1 == null ? null : class1.getClassLoader();
        final ClassLoader loader2 = class2 == null ? null : class2.getClassLoader();

        if (isChild(threadContextClassLoader, loader1)) {
            return isChild(threadContextClassLoader, loader2) ? threadContextClassLoader : loader2;
        }
        return isChild(loader1, loader2) ? loader1 : loader2;
    }

    /**
     * This method will search for {@code resource} in different
     * places. The search order is as follows:
     *
     * <ol>
     *
     * <li>Search for {@code resource} using the thread context
     * class loader under Java2. If that fails, search for
     * {@code resource} using the class loader that loaded this
     * class ({@code Loader}). Under JDK 1.1, only the class
     * loader that loaded this class ({@code Loader}) is used.</li>
     * <li>Try one last time with
     * {@code ClassLoader.getSystemResource(resource)}, that is
     * using the system class loader in JDK 1.2 and virtual machine's
     * built-in class loader in JDK 1.1.</li>
     * </ol>
     * @param resource The resource to load.
     * @param defaultLoader The default ClassLoader.
     * @return A URL to the resource.
     */
    public static URL getResource(final String resource, final ClassLoader defaultLoader) {
        try {
            ClassLoader classLoader = getThreadContextClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using context class loader {}.", resource, classLoader);
                final URL url = classLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }

            // We could not find resource. Let us now try with the classloader that loaded this class.
            classLoader = Loader.class.getClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, classLoader);
                final URL url = classLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }
            // We could not find resource. Finally try with the default ClassLoader.
            if (defaultLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, defaultLoader);
                final URL url = defaultLoader.getResource(resource);
                if (url != null) {
                    return url;
                }
            }
        } catch (final Throwable t) {
            //
            //  can't be InterruptedException or InterruptedIOException
            //    since not declared, must be error or RuntimeError.
            LOGGER.warn(TSTR, t);
        }

        // Last ditch attempt: get the resource from the class path. It
        // may be the case that clazz was loaded by the Extension class
        // loader which the parent of the system class loader. Hence the
        // code below.
        LOGGER.trace("Trying to find [{}] using ClassLoader.getSystemResource().", resource);
        return ClassLoader.getSystemResource(resource);
    }

    /**
     * This method will search for {@code resource} in different
     * places. The search order is as follows:
     *
     * <ol>
     * <li>Search for {@code resource} using the thread context
     * class loader under Java2. If that fails, search for
     * {@code resource} using the class loader that loaded this
     * class ({@code Loader}). Under JDK 1.1, only the class
     * loader that loaded this class ({@code Loader}) is used.</li>
     * <li>Try one last time with
     * {@code ClassLoader.getSystemResource(resource)}, that is
     * using the system class loader in JDK 1.2 and virtual machine's
     * built-in class loader in JDK 1.1.</li>
     * </ol>
     * @param resource The resource to load.
     * @param defaultLoader The default ClassLoader.
     * @return An InputStream to read the resouce.
     */
    public static InputStream getResourceAsStream(final String resource, final ClassLoader defaultLoader) {
        try {
            ClassLoader classLoader = getThreadContextClassLoader();
            InputStream is;
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using context class loader {}.", resource, classLoader);
                is = classLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }

            // We could not find resource. Let us now try with the classloader that loaded this class.
            classLoader = Loader.class.getClassLoader();
            if (classLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, classLoader);
                is = classLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }

            // We could not find resource. Finally try with the default ClassLoader.
            if (defaultLoader != null) {
                LOGGER.trace("Trying to find [{}] using {} class loader.", resource, defaultLoader);
                is = defaultLoader.getResourceAsStream(resource);
                if (is != null) {
                    return is;
                }
            }
        } catch (final Throwable t) {
            //
            //  can't be InterruptedException or InterruptedIOException
            //    since not declared, must be error or RuntimeError.
            LOGGER.warn(TSTR, t);
        }

        // Last ditch attempt: get the resource from the class path. It
        // may be the case that clazz was loaded by the Extension class
        // loader which the parent of the system class loader. Hence the
        // code below.
        LOGGER.trace("Trying to find [{}] using ClassLoader.getSystemResource().", resource);
        return ClassLoader.getSystemResourceAsStream(resource);
    }

    /**
     * Determines if one ClassLoader is a child of another ClassLoader. Note that a {@code null} ClassLoader is
     * interpreted as the system ClassLoader as per convention.
     *
     * @param loader1 the ClassLoader to check for childhood.
     * @param loader2 the ClassLoader to check for parenthood.
     * @return {@code true} if the first ClassLoader is a strict descendant of the second ClassLoader.
     */
    private static boolean isChild(final ClassLoader loader1, final ClassLoader loader2) {
        if (loader1 != null && loader2 != null) {
            ClassLoader parent = loader1.getParent();
            while (parent != null && parent != loader2) {
                parent = parent.getParent();
            }
            // once parent is null, we're at the system CL, which would indicate they have separate ancestry
            return parent != null;
        }
        return loader1 != null;
    }

    /**
     * Loads and initializes a named Class using a given ClassLoader.
     *
     * @param className The class name.
     * @param loader The class loader.
     * @return The class.
     * @throws ClassNotFoundException if the class could not be found.
     */
    public static Class<?> initializeClass(final String className, final ClassLoader loader)
            throws ClassNotFoundException {
        return Class.forName(className, true, loader);
    }

    /**
     * Loads a named Class using a given ClassLoader.
     *
     * @param className The class name.
     * @param loader The class loader.
     * @return The class, or null if loader is null.
     * @throws ClassNotFoundException if the class could not be found.
     */
    public static Class<?> loadClass(final String className, final ClassLoader loader)
            throws ClassNotFoundException {
        return loader != null ? loader.loadClass(className) : null;
    }

    /**
     * Load a Class in the {@code java.*} namespace by name. Useful for peculiar scenarios typically involving
     * Google App Engine.
     *
     * @param className The class name.
     * @return The Class.
     * @throws ClassNotFoundException if the Class could not be found.
     */
    public static Class<?> loadSystemClass(final String className) throws ClassNotFoundException {
        try {
            return Class.forName(className, true, ClassLoader.getSystemClassLoader());
        } catch (final Throwable t) {
            LOGGER.trace("Couldn't use SystemClassLoader. Trying Class.forName({}).", className, t);
            return Class.forName(className);
        }
    }

    /**
     * Loads and instantiates a Class using the default constructor.
     *
     * @param className The class name.
     * @return new instance of the class.
     * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException if the class can't be instantiated through a public constructor
     * @throws InstantiationException if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     */
    @SuppressWarnings("unchecked")
    public static <T> T newInstanceOf(final String className)
        throws ClassNotFoundException,
        IllegalAccessException,
        InstantiationException,
        NoSuchMethodException,
        InvocationTargetException {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newInstanceOf(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Loads, instantiates, and casts a Class using the default constructor.
     *
     * @param className The class name.
     * @param clazz The class to cast it to.
     * @param <T> The type to cast it to.
     * @return new instance of the class cast to {@code T}
     * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException if the class can't be instantiated through a public constructor
     * @throws InstantiationException if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     * @throws ClassCastException if the constructed object isn't type compatible with {@code T}
     */
    public static <T> T newCheckedInstanceOf(final String className, final Class<T> clazz)
        throws ClassNotFoundException,
        NoSuchMethodException,
        IllegalAccessException,
        InvocationTargetException,
        InstantiationException {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newCheckedInstanceOf(className, clazz);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Loads and instantiates a class given by a property name.
     *
     * @param propertyName The property name to look up a class name for.
     * @param clazz        The class to cast it to.
     * @param <T>          The type to cast it to.
     * @return new instance of the class given in the property or {@code null} if the property was unset.
     * @throws ClassNotFoundException    if the class isn't available to the usual ClassLoaders
     * @throws IllegalAccessException    if the class can't be instantiated through a public constructor
     * @throws InstantiationException    if there was an exception whilst instantiating the class
     * @throws NoSuchMethodException     if there isn't a no-args constructor on the class
     * @throws InvocationTargetException if there was an exception whilst constructing the class
     * @throws ClassCastException        if the constructed object isn't type compatible with {@code T}
     */
    public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
        throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
        IllegalAccessException {
        final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.newCheckedInstanceOfProperty(propertyName, clazz);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    /**
     * Determines if a named Class can be loaded or not.
     *
     * @param className The class name.
     * @return {@code true} if the class could be found or {@code false} otherwise.
     */
    public static boolean isClassAvailable(final String className) {
        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.isClassAvailable(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }

    public static boolean isJansiAvailable() {
        return isClassAvailable("org.fusesource.jansi.AnsiRenderer");
    }

    /**
     * Loads a class by name. This method respects the {@link #IGNORE_TCCL_PROPERTY} Log4j property. If this property is
     * specified and set to anything besides {@code false}, then the default ClassLoader will be used.
     *
     * @param className The class name.
     * @return the Class for the given name.
     * @throws ClassNotFoundException if the specified class name could not be found
     */
    public static Class<?> loadClass(final String className) throws ClassNotFoundException {

        final ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        try {
            Thread.currentThread().setContextClassLoader(getClassLoader());
            return LoaderUtil.loadClass(className);
        } finally {
            Thread.currentThread().setContextClassLoader(contextClassLoader);
        }
    }
}
