package co.codewizards.cloudstore.local.persistence;

import static java.util.Objects.*;

import java.util.Date;

import javax.jdo.JDOHelper;
import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.Inheritance;
import javax.jdo.annotations.InheritanceStrategy;
import javax.jdo.annotations.NotPersistent;
import javax.jdo.annotations.NullValue;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

/**
 * Base class of all persistence-capable (a.k.a. entity) classes.
 * @author Marco หงุ่ยตระกูล-Schulze - marco at codewizards dot co
 */
@PersistenceCapable(identityType=IdentityType.APPLICATION)
@Inheritance(strategy=InheritanceStrategy.SUBCLASS_TABLE)
public abstract class Entity implements AutoTrackChanged
{
        @PrimaryKey
        @Persistent(valueStrategy=IdGeneratorStrategy.NATIVE)
        private long id = Long.MIN_VALUE;

        // We always initialise this, though the value might be overwritten when DataNucleus loads
        // the object's data from the DB. There's no need to defer the Date instantiation.
        // Creating 1 million instances of Date costs less than 68 ms (I tested creating them and
        // putting them into a LinkedList (preventing optimizer short-cuts), so the LinkedList
        // overhead is included in this time).
        @Persistent(nullValue=NullValue.EXCEPTION)
        private Date created = new Date();

        @Persistent(nullValue=NullValue.EXCEPTION)
        private Date changed = new Date();

        @NotPersistent
        private transient int hashCode;

        /**
         * Get the unique identifier of this object.
         * <p>
         * This identifier is unique per entity type (the first sub-class of this class
         * having an own table - which is usually the direct sub-class of {@link Entity}).
         * <p>
         * This identifier is assigned when the object is persisted into the DB.
         * @return the unique identifier of this object.
         */
        public long getId() {
                return id;
        }

        @Override
        public boolean equals(final Object obj) {
                if (this == obj) {
                        return true;
                }
                if (obj == null) {
                        return false;
                }

                final Object thisOid = JDOHelper.getObjectId(this);
                if (thisOid == null) {
                        return false;
                }

                final Object otherOid = JDOHelper.getObjectId(obj);
                return thisOid.equals(otherOid);
        }

        @Override
        public int hashCode() {
                if (hashCode == 0) {
                        // Freeze the hashCode.
                        //
                        // We make sure the hashCode does not change after it was once initialised, because the object might
                        // have been added to a HashSet (or Map) before being persisted. During persistence, the object's id is
                        // assigned and without freezing the hashCode, the object is thus not found in the Map/Set, anymore.
                        //
                        // This new strategy seems to be working well; messages like this do not occur anymore:
                        //
                        // Aug 22, 2014 9:44:23 AM org.datanucleus.store.rdbms.mapping.java.PersistableMapping postInsert
                        // INFO: Object "co.codewizards.cloudstore.local.persistence.FileChunk@36dccbc7" has field "co.codewizards.cloudstore.local.persistence.FileChunk.normalFile" with an N-1 bidirectional relation set to relate to "co.codewizards.cloudstore.local.persistence.NormalFile@63323bb" but the collection at "co.codewizards.cloudstore.local.persistence.NormalFile.fileChunks" doesnt contain this object.

                        final Object thisOid = JDOHelper.getObjectId(this);
                        if (thisOid == null)
                                hashCode = super.hashCode();
                        else
                                hashCode = thisOid.hashCode();

                        if (hashCode == 0) // very unlikely, but we want our code to be 100% robust.
                                hashCode = 1;
                }
                return hashCode;
        }

        @Override
        public String toString() {
                return getClass().getSimpleName() + '[' + toString_getProperties() + ']';
        }

        protected String toString_getProperties() {
                return "id=" + JDOHelper.getObjectId(this);
        }

        /**
         * Gets the timestamp of the creation of this entity.
         * @return the timestamp of the creation of this entity. Never <code>null</code>.
         */
        public Date getCreated() {
                return created;
        }
        /**
         * Sets the timestamp of the creation of this entity.
         * <p>
         * <b>Important: You should normally never invoke this method!</b> The {@code created} property
         * is supposed to be read-only (assigned once during object creation and never again).
         * This setter merely exists for extraordinary, unforeseen use cases as well as tests.
         * @param created the timestamp of the creation of this entity. Must not be <code>null</code>.
         */
        protected void setCreated(final Date created) {
                requireNonNull(created, "created");
                this.created = created;
        }

        @Override
        public Date getChanged() {
                return changed;
        }
        @Override
        public void setChanged(final Date changed) {
                requireNonNull(created, "created");
                this.changed = changed;
        }

}