/*
 * 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.openjpa.enhance;

import java.util.Collection;
import java.util.Collections;
import java.util.Map;

import org.apache.openjpa.lib.util.Localizer;
import org.apache.openjpa.lib.util.collections.AbstractReferenceMap;
import org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashMap;
import org.apache.openjpa.lib.util.concurrent.ConcurrentReferenceHashSet;
import org.apache.openjpa.util.UserException;

/**
 * Tracks registered persistence-capable classes.
 *
 * @since 0.4.0
 * @author Abe White
 */
public class PCRegistry {
    // DO NOT ADD ADDITIONAL DEPENDENCIES TO THIS CLASS

    private static final Localizer _loc = Localizer.forPackage(PCRegistry.class);

    // map of persistent classes to meta structures; weak so the VM can GC classes
    private static final Map<Class<?>,Meta> _metas = new ConcurrentReferenceHashMap(
            AbstractReferenceMap.ReferenceStrength.WEAK,
            AbstractReferenceMap.ReferenceStrength.HARD);

    // register class listeners
    // Weak reference prevents OutOfMemeoryError as described in OPENJPA-2042
    private static final Collection<RegisterClassListener> _listeners =
        new ConcurrentReferenceHashSet<>(
                AbstractReferenceMap.ReferenceStrength.WEAK);

    /**
     * Register a {@link RegisterClassListener}.
     */
    public static void addRegisterClassListener(RegisterClassListener rcl) {
        if (rcl == null)
            return;

        // we have to be positive that every listener gets notified for
        // every class, so lots of locking
        synchronized (_listeners) {
            _listeners.add(rcl);
        }
        synchronized (_metas) {
            for (Class<?> cls : _metas.keySet())
                rcl.register(cls);
        }
    }

    /**
     * Removes a {@link RegisterClassListener}.
     */
    public static boolean removeRegisterClassListener(RegisterClassListener rcl) {
        synchronized (_listeners) {
            return _listeners.remove(rcl);
        }
    }

    /**
     * Get the field names for a <code>PersistenceCapable</code> class.
     */
    public static String[] getFieldNames(Class<?> pcClass) {
        Meta meta = getMeta(pcClass);
        return meta.fieldNames;
    }

    /**
     * Get the field types for a <code>PersistenceCapable</code> class.
     */
    public static Class<?>[] getFieldTypes(Class<?> pcClass) {
        Meta meta = getMeta(pcClass);
        return meta.fieldTypes;
    }

    /**
     * Return the persistent superclass for a <code>PersistenceCapable</code>
     * class, or null if none. The superclass may or may not implement
     * {@link PersistenceCapable}, depending on the access type of the class.
     */
    public static Class<?> getPersistentSuperclass(Class<?> pcClass) {
        Meta meta = getMeta(pcClass);
        return meta.pcSuper;
    }

    /**
     * Create a new instance of the class and assign its state manager.
     * The new instance has its flags set to <code>LOAD_REQUIRED</code>.
     */
    public static PersistenceCapable newInstance(Class<?> pcClass, StateManager sm, boolean clear) {
        Meta meta = getMeta(pcClass);
        return (meta.pc == null) ? null : meta.pc.pcNewInstance(sm, clear);
    }

    /**
     * Create a new instance of the class and assign its state manager and oid.
     * The new instance has its flags set to <code>LOAD_REQUIRED</code>.
     */
    public static PersistenceCapable newInstance(Class<?> pcClass, StateManager sm, Object oid, boolean clear) {
        Meta meta = getMeta(pcClass);
        return (meta.pc == null) ? null : meta.pc.pcNewInstance(sm, oid, clear);
    }

    /**
     * Return the persistence-capable type for <code>type</code>. This might
     * be a generated subclass of <code>type</code>.
     *
     * @since 1.1.0
     */
    public static Class<?> getPCType(Class<?> type) {
        Meta meta = getMeta(type);
        return (meta.pc == null) ? null : meta.pc.getClass();
    }

    /**
     * Create a new identity object for the given
     * <code>PersistenceCapable</code> class.
     */
    public static Object newObjectId(Class<?> pcClass) {
        Meta meta = getMeta(pcClass);
        return (meta.pc == null) ? null : meta.pc.pcNewObjectIdInstance();
    }

    /**
     * Create a new identity object for the given
     * <code>PersistenceCapable</code> class, using the <code>String</code>
     * form of the constructor.
     */
    public static Object newObjectId(Class<?> pcClass, String str) {
        Meta meta = getMeta(pcClass);
        return (meta.pc == null) ? null : meta.pc.pcNewObjectIdInstance(str);
    }

    /**
     * Return the alias for the given type.
     */
    public static String getTypeAlias(Class<?> pcClass) {
        return getMeta(pcClass).alias;
    }

    /**
     * Copy fields from an outside source to the key fields in the identity
     * object.
     */
    public static void copyKeyFieldsToObjectId(Class<?> pcClass, FieldSupplier fm, Object oid) {
        Meta meta = getMeta(pcClass);
        if (meta.pc == null)
            throw new UserException(_loc.get("copy-no-id", pcClass));

        meta.pc.pcCopyKeyFieldsToObjectId(fm, oid);
    }

    /**
     * Copy fields to an outside source from the key fields in the identity
     * object.
     */
    public static void copyKeyFieldsFromObjectId(Class<?> pcClass, FieldConsumer fm, Object oid) {
        Meta meta = getMeta(pcClass);
        if (meta.pc == null)
            throw new UserException(_loc.get("copy-no-id", pcClass));

        meta.pc.pcCopyKeyFieldsFromObjectId(fm, oid);
    }

    /**
     * Register metadata by class.
     *
     * @param fieldTypes managed field types
     * @param fieldFlags managed field flags
     * @param sup the most immediate persistent superclass
     * @param pcClass the <code>PersistenceCapable</code> class
     * @param fieldNames managed field names
     * @param alias the class alias
     * @param pc an instance of the class, if not abstract
     */
    public static void register(Class<?> pcClass, String[] fieldNames, Class<?>[] fieldTypes, byte[] fieldFlags,
        Class<?> sup, String alias, PersistenceCapable pc) {
        if (pcClass == null)
            throw new NullPointerException();

        // we have to be positive that every listener gets notified for
        // every class, so lots of locking
        Meta meta = new Meta(pc, fieldNames, fieldTypes, sup, alias);
        synchronized (_metas) {
            _metas.put(pcClass, meta);
        }
        synchronized (_listeners) {
            for (RegisterClassListener r : _listeners){
                if (r != null) {
                    r.register(pcClass);
                }
            }
        }
    }

    /**
     * De-Register all metadata associated with the given ClassLoader.
     * Allows ClassLoaders to be garbage collected.
     *
     * @param cl the ClassLoader
     */
    public static void deRegister(ClassLoader cl) {
        synchronized (_metas) {
            for (Class<?> pcClass : _metas.keySet()) {
                if (pcClass.getClassLoader() == cl) {
                    _metas.remove(pcClass);
                }
            }
        }
    }

    /**
     * Returns a collection of class objects of the registered
     * persistence-capable classes.
     */
    public static Collection<Class<?>> getRegisteredTypes() {
        return Collections.unmodifiableCollection(_metas.keySet());
    }

    /**
     * Returns <code>true</code> if the given class is already registered.
     */
    public static boolean isRegistered(Class<?> cls) {
        return _metas.containsKey(cls);
    }

    /**
     * Look up the metadata for a <code>PersistenceCapable</code> class.
     */
    private static Meta getMeta(Class<?> pcClass) {
        Meta ret = (Meta) _metas.get(pcClass);
        if (ret == null)
            throw new IllegalStateException(_loc.get("no-meta", pcClass).
                getMessage());
        return ret;
    }

    /**
     * Listener for persistent class registration events.
     */
    public interface RegisterClassListener {

        void register(Class<?> cls);
    }

    /**
     * This is a helper class to manage metadata per persistence-capable class.
     */
    private static class Meta {

        public final PersistenceCapable pc;
        public final String[] fieldNames;
        public final Class<?>[] fieldTypes;
        public final Class<?> pcSuper;
        public final String alias;

        public Meta(PersistenceCapable pc, String[] fieldNames,
            Class<?>[] fieldTypes, Class<?> pcSuper, String alias) {
            this.pc = pc;
            this.fieldNames = fieldNames;
            this.fieldTypes = fieldTypes;
            this.pcSuper = pcSuper;
			this.alias = alias;
		}
	}
}