/*
 * Copyright (c) 2015, 2020, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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
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 */

package jdk.internal.module;

import java.lang.module.Configuration;
import java.lang.module.ResolvedModule;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;

import jdk.internal.loader.ClassLoaders;

/**
 * Supports the mapping of modules to class loaders. The set of modules mapped
 * to the boot and platform class loaders is generated at build time from
 * this source file.
 */
public final class ModuleLoaderMap {

    private static final ClassLoader PLATFORM_CLASSLOADER =
            ClassLoaders.platformClassLoader();
    private static final ClassLoader APP_CLASSLOADER =
            ClassLoaders.appClassLoader();

    // Using boxed values allows us to use these as an adhoc enum, while keeping
    // comparisons in Mapper.apply cheap during bootstrap since we can do
    // identity comparisons rather than unbox the value. Not storing a reference
    // to the ClassLoader directly ensures we can archive Mapper instances
    private static final Integer PLATFORM_LOADER_INDEX = 1;
    private static final Integer APP_LOADER_INDEX      = 2;

    /**
     * Maps the system modules to the built-in class loaders.
     */
    public static final class Mapper implements Function<String, ClassLoader> {
        private final Map<String, Integer> map;

        Mapper(Map<String, Integer> map) {
            this.map = map; // defensive copy not needed
        }

        @Override
        public ClassLoader apply(String name) {
            Integer loader = map.get(name);
            if (loader == APP_LOADER_INDEX) {
                return APP_CLASSLOADER;
            } else if (loader == PLATFORM_LOADER_INDEX) {
                return PLATFORM_CLASSLOADER;
            } else { // BOOT_LOADER_INDEX
                return null;
            }
        }
    }

    /**
     * Returns the names of the modules defined to the boot loader.
     */
    public static Set<String> bootModules() {
        return Modules.bootModules;
    }

    /**
     * Returns the names of the modules defined to the platform loader.
     */
    public static Set<String> platformModules() {
        return Modules.platformModules;
    }

    private static class Modules {
        // list of boot modules is generated at build time.
        private static final Set<String> bootModules =
                Set.of(new String[] { "@@BOOT_MODULE_NAMES@@" });

        // list of platform modules is generated at build time.
        private static final Set<String> platformModules =
                Set.of(new String[] { "@@PLATFORM_MODULE_NAMES@@" });
    }

    /**
     * Returns a function to map modules in the given configuration to the
     * built-in class loaders.
     */
    static Mapper mappingFunction(Configuration cf) {
        var map = new HashMap<String, Integer>();
        for (ResolvedModule resolvedModule : cf.modules()) {
            String mn = resolvedModule.name();
            if (!Modules.bootModules.contains(mn)) {
                if (Modules.platformModules.contains(mn)) {
                    map.put(mn, PLATFORM_LOADER_INDEX);
                } else {
                    map.put(mn, APP_LOADER_INDEX);
                }
            }
        }
        return new Mapper(map);
    }
}