/*
 * Copyright 2015 Open Networking Laboratory
 *
 * 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.onosproject.security;

import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;

import com.google.common.annotations.Beta;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

import java.lang.reflect.Field;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

/**
 * Aids SM-ONOS to perform API-level permission checking.
 */
@Beta
public final class AppGuard {
    private AppGuard() {
    }

    /**
     * Checks if the caller has the required permission only when security-mode is enabled.
     *
     * @param permission permission to be checked
     */
    public static void checkPermission(AppPermission.Type permission) {

        SecurityManager sm = System.getSecurityManager();
        if (sm == null) {
            return;
        }

        Object result = AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
            int contextHash = 0;
            AccessControlContext context = AccessController.getContext();
            Field f = null;
            try {
                f = context.getClass().getDeclaredField("context");

                f.setAccessible(true);
                ProtectionDomain[] domain = (ProtectionDomain[]) f.get(context);
                for (ProtectionDomain pd : domain) {
                    if (pd.getCodeSource() != null) {
                        contextHash = contextHash ^ pd.getCodeSource().getLocation().hashCode();
                    } else {
                        return null;
                    }
                }
                return contextHash;
            } catch (NoSuchFieldException e) {
                return null;
            } catch (IllegalAccessException e) {
                return null;
            }
        });

        if (result == null) {
            sm.checkPermission(new AppPermission(permission));
        } else {
            AppPermission perm = new AppPermission(permission);
            int hash = ((int) result) ^ perm.hashCode();
            PermissionCheckCache.getInstance().checkCache(hash, perm);
        }
    }


    private static final class PermissionCheckCache {

        private static final Cache<Integer, Boolean> CACHE = CacheBuilder.newBuilder()
                .maximumSize(1000)
                .expireAfterAccess(10, TimeUnit.MINUTES)
                .build();

        private PermissionCheckCache() {
        }

        private static class SingletonHelper {
            private static final PermissionCheckCache INSTANCE = new PermissionCheckCache();
        }

        public static PermissionCheckCache getInstance() {
            return SingletonHelper.INSTANCE;
        }

        public static void checkCache(int key, AppPermission perm) {
            try {
                CACHE.get(key, () -> {
                    System.getSecurityManager().checkPermission(perm);
                    return true;
                });
            } catch (ExecutionException e) {
                System.getSecurityManager().checkPermission(perm);
            }
        }
    }

}