/*

 * Copyright (c) 2014, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.vm.ci.services;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.util.ArrayList;

import java.util.Collections;

import java.util.Formatter;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.ServiceLoader;

import java.util.Set;

import jdk.internal.misc.VM;

import jdk.internal.reflect.Reflection;

/**

 * Provides utilities needed by JVMCI clients.

 */

public final class Services {

    /**

     * Guards code that should be run when building an JVMCI shared library but should be excluded

     * from (being compiled into) the library. Such code must be directly guarded by an {@code if}

     * statement on this field - the guard cannot be behind a method call.

     */

    public static final boolean IS_BUILDING_NATIVE_IMAGE = Boolean.parseBoolean(VM.getSavedProperty("jdk.vm.ci.services.aot"));

    /**

     * Guards code that should only be run in a JVMCI shared library. Such code must be directly

     * guarded by an {@code if} statement on this field - the guard cannot be behind a method call.

     *

     * The value of this field in a JVMCI shared library runtime must be {@code true}.

     */

    public static final boolean IS_IN_NATIVE_IMAGE;

    static {

        /*

         * Prevents javac from constant folding use of this field. It is set to true by the process

         * that builds the shared library.

         */

        IS_IN_NATIVE_IMAGE = false;

    }

    private Services() {

    }

    /**

     * Checks that JVMCI is enabled in the VM and throws an error if it isn't.

     */

    static void checkJVMCIEnabled() {

        if (!JVMCI_ENABLED) {

            throw new Error("The EnableJVMCI VM option must be true (i.e., -XX:+EnableJVMCI) to use JVMCI");

        }

    }

    /**

     * Gets an unmodifiable copy of the system properties saved when {@link System} is initialized.

     */

    public static Map<String, String> getSavedProperties() {

        checkJVMCIEnabled();

        }

        return savedProperties;

    }

    /**

     * Helper method equivalent to {@link #getSavedProperties()}{@code .getOrDefault(name, def)}.

     */

    public static String getSavedProperty(String name, String def) {

        return Services.getSavedProperties().getOrDefault(name, def);

    }

    /**

     * Helper method equivalent to {@link #getSavedProperties()}{@code .get(name)}.

     */

    public static String getSavedProperty(String name) {

        return Services.getSavedProperties().get(name);

    }

    /**

     * Causes the JVMCI subsystem to be initialized if it isn't already initialized.

     */

    public static void initializeJVMCI() {

        checkJVMCIEnabled();

        try {

            Class.forName("jdk.vm.ci.runtime.JVMCI");

        } catch (ClassNotFoundException e) {

            throw new InternalError(e);

        }

    }

    private static boolean jvmciEnabled = true;

    /**

     * When {@code -XX:-UseJVMCIClassLoader} is in use, JVMCI classes are loaded via the boot class

     * loader. When {@code null} is the second argument to

     * {@link ServiceLoader#load(Class, ClassLoader)}, service lookup will use the system class

     * loader and thus find application classes which violates the API of {@link #load} and

     * {@link #loadSingle}. To avoid this, a class loader that simply delegates to the boot class

     * loader is used.

     */

    static class LazyBootClassPath {

        static final ClassLoader bootClassPath = new ClassLoader(null) {

        };

    }

    private static ClassLoader findBootClassLoaderChild(ClassLoader start) {

        ClassLoader cl = start;

        while (cl.getParent() != null) {

            cl = cl.getParent();

        }

        return cl;

    }

    private static final Map<Class<?>, List<?>> servicesCache = IS_BUILDING_NATIVE_IMAGE ? new HashMap<>() : null;

    @SuppressWarnings("unchecked")

    private static <S> Iterable<S> load0(Class<S> service) {

        if (IS_IN_NATIVE_IMAGE || IS_BUILDING_NATIVE_IMAGE) {

            List<?> list = servicesCache.get(service);

            if (list != null) {

                return (Iterable<S>) list;

            }

            if (IS_IN_NATIVE_IMAGE) {

                throw new InternalError(String.format("No %s providers found when building native image", service.getName()));

            }

        }

        Iterable<S> providers = Collections.emptyList();

        if (jvmciEnabled) {

            ClassLoader cl = null;

            try {

                cl = getJVMCIClassLoader();

                if (cl == null) {

                    cl = LazyBootClassPath.bootClassPath;

                    // JVMCI classes are loaded via the boot class loader.

                    // If we use null as the second argument to ServiceLoader.load,

                    // service loading will use the system class loader

                    // and find classes on the application class path. Since we

                    // don't want this, we use a loader that is as close to the

                    // boot class loader as possible (since it is impossible

                    // to force service loading to use only the boot class loader).

                    cl = findBootClassLoaderChild(ClassLoader.getSystemClassLoader());

                }

                providers = ServiceLoader.load(service, cl);

            } catch (UnsatisfiedLinkError e) {

                jvmciEnabled = false;

            } catch (InternalError e) {

                if (e.getMessage().equals("JVMCI is not enabled")) {

                    jvmciEnabled = false;

                } else {

                    throw e;

                }

            }

        }

        if (IS_BUILDING_NATIVE_IMAGE) {

            synchronized (servicesCache) {

                ArrayList<S> providersList = new ArrayList<>();

                for (S provider : providers) {

                    providersList.add(provider);

                }

                servicesCache.put(service, providersList);

                providers = providersList;

            }

        }

        return providers;

    }

    /**

     * Opens all JVMCI packages to {@code otherModule}.

     */

    static void openJVMCITo(Module otherModule) {

        Module jvmci = Services.class.getModule();

        if (jvmci != otherModule) {

            Set<String> packages = jvmci.getPackages();

            for (String pkg : packages) {

                boolean opened = jvmci.isOpen(pkg, otherModule);

                if (!opened) {

                    jvmci.addOpens(pkg, otherModule);

                }

            }

        }

    }

    /**

     * Gets an {@link Iterable} of the JVMCI providers available for a given service.

     *

     * @throws SecurityException if a security manager is present and it denies <tt>

     *             {@link RuntimePermission}("jvmci")</tt>

     */

    public static <S> Iterable<S> load(Class<S> service) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        return load0(service);

    }

    /**

     * Gets the JVMCI provider for a given service for which at most one provider must be available.

     *

     * @param service the service whose provider is being requested

     * @param required specifies if an {@link InternalError} should be thrown if no provider of

     *            {@code service} is available

     * @throws SecurityException if a security manager is present and it denies <tt>

     *             {@link RuntimePermission}("jvmci")</tt>

     */

    public static <S> S loadSingle(Class<S> service, boolean required) {

        SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(new JVMCIPermission());

        }

        Iterable<S> providers = load0(service);

        S singleProvider = null;

        for (S provider : providers) {

            if (singleProvider != null) {

                throw new InternalError(String.format("Multiple %s providers found: %s, %s", service.getName(), singleProvider.getClass().getName(), provider.getClass().getName()));

            }

            singleProvider = provider;

        }

        if (singleProvider == null && required) {

            String javaHome = Services.getSavedProperty("java.home");

            String vmName = Services.getSavedProperty("java.vm.name");

            Formatter errorMessage = new Formatter();

            errorMessage.format("The VM does not expose required service %s.%n", service.getName());

            errorMessage.format("Currently used Java home directory is %s.%n", javaHome);

            errorMessage.format("Currently used VM configuration is: %s", vmName);

            throw new UnsupportedOperationException(errorMessage.toString());

        }

        return singleProvider;

    }

    static {

        Reflection.registerMethodsToFilter(Services.class, Set.of("getJVMCIClassLoader"));

    }

    /**

     * Gets the JVMCI class loader.

     *

     * @throws InternalError with the {@linkplain Throwable#getMessage() message}

     *             {@code "JVMCI is not enabled"} iff JVMCI is not enabled

     */

    private static ClassLoader getJVMCIClassLoader() {

        if (IS_IN_NATIVE_IMAGE) {

            return null;

        }

        return ClassLoader.getSystemClassLoader();

    }

    /**

     * A Java {@code char} has a maximal UTF8 length of 3.

     */

    private static final int MAX_UNICODE_IN_UTF8_LENGTH = 3;

    /**

     * {@link DataOutputStream#writeUTF(String)} only supports values whose UTF8 encoding length is

     * less than 65535.

     */

    private static final int MAX_UTF8_PROPERTY_STRING_LENGTH = 65535 / MAX_UNICODE_IN_UTF8_LENGTH;

    /**

     * Serializes the {@linkplain #getSavedProperties() saved system properties} to a byte array for

     * the purpose of {@linkplain #initializeSavedProperties(byte[]) initializing} the initial

     * properties in the JVMCI shared library.

     */

    @VMEntryPoint

    private static byte[] serializeSavedProperties() throws IOException {

        if (IS_IN_NATIVE_IMAGE) {

            throw new InternalError("Can only serialize saved properties in HotSpot runtime");

        }

        return serializeProperties(Services.getSavedProperties());

    }

    private static byte[] serializeProperties(Map<String, String> props) throws IOException {

        // Compute size of output on the assumption that

        // all system properties have ASCII names and values

        int estimate = 4 + 4;

        int nonUtf8Props = 0;

        for (Map.Entry<String, String> e : props.entrySet()) {

            String name = e.getKey();

            String value = e.getValue();

            estimate += (2 + (name.length())) + (2 + (value.length()));

            if (name.length() > MAX_UTF8_PROPERTY_STRING_LENGTH || value.length() > MAX_UTF8_PROPERTY_STRING_LENGTH) {

                nonUtf8Props++;

            }

        }

        ByteArrayOutputStream baos = new ByteArrayOutputStream(estimate);

        DataOutputStream out = new DataOutputStream(baos);

        out.writeInt(props.size() - nonUtf8Props);

        out.writeInt(nonUtf8Props);

        for (Map.Entry<String, String> e : props.entrySet()) {

            String name = e.getKey();

            String value = e.getValue();

            if (name.length() <= MAX_UTF8_PROPERTY_STRING_LENGTH && value.length() <= MAX_UTF8_PROPERTY_STRING_LENGTH) {

                out.writeUTF(name);

                out.writeUTF(value);

            }

        }

        if (nonUtf8Props != 0) {

            for (Map.Entry<String, String> e : props.entrySet()) {

                String name = e.getKey();

                String value = e.getValue();

                if (name.length() > MAX_UTF8_PROPERTY_STRING_LENGTH || value.length() > MAX_UTF8_PROPERTY_STRING_LENGTH) {

                    byte[] utf8Name = name.getBytes("UTF-8");

                    byte[] utf8Value = value.getBytes("UTF-8");

                    out.writeInt(utf8Name.length);

                    out.write(utf8Name);

                    out.writeInt(utf8Value.length);

                    out.write(utf8Value);

                }

            }

        }

        return baos.toByteArray();

    }

    /**

     * Initialized the {@linkplain #getSavedProperties() saved system properties} in the JVMCI

     * shared library from the {@linkplain #serializeSavedProperties() serialized saved properties}

     * in the HotSpot runtime.

     */

    @VMEntryPoint

    private static void initializeSavedProperties(byte[] serializedProperties) throws IOException {

        if (!IS_IN_NATIVE_IMAGE) {

            throw new InternalError("Can only initialize saved properties in JVMCI shared library runtime");

        }

        savedProperties = Collections.unmodifiableMap(deserializeProperties(serializedProperties));

    }

    private static Map<String, String> deserializeProperties(byte[] serializedProperties) throws IOException {

        DataInputStream in = new DataInputStream(new ByteArrayInputStream(serializedProperties));

        int utf8Props = in.readInt();

        int nonUtf8Props = in.readInt();

        Map<String, String> props = new HashMap<>(utf8Props + nonUtf8Props);

        int index = 0;

        while (in.available() != 0) {

            if (index < utf8Props) {

                String name = in.readUTF();

                String value = in.readUTF();

                props.put(name, value);

            } else {

                int nameLen = in.readInt();

                byte[] nameBytes = new byte[nameLen];

                in.read(nameBytes);

                int valueLen = in.readInt();

                byte[] valueBytes = new byte[valueLen];

                in.read(valueBytes);

                String name = new String(nameBytes, "UTF-8");

                String value = new String(valueBytes, "UTF-8");

                props.put(name, value);

            }

            index++;

        }

        return props;

    }

}