/*****************************************************************
 *   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.cayenne.map;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.event.EventManager;
import org.apache.cayenne.event.EventSubject;
import org.apache.cayenne.map.event.RelationshipEvent;
import org.apache.cayenne.util.Util;
import org.apache.cayenne.util.XMLEncoder;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.collections.Transformer;

/**
 * A DbRelationship is a descriptor of a database inter-table relationship based on one or
 * more primary key/foreign key pairs.
 * 
 * @author Misha Shengaout
 * @author Andrus Adamchik
 */
public class DbRelationship extends Relationship {

    // DbRelationship events
    public static final EventSubject PROPERTY_DID_CHANGE = EventSubject.getSubject(
            DbRelationship.class,
            "PropertyDidChange");

    // The columns through which the join is implemented.
    protected List<DbJoin> joins = new ArrayList<DbJoin>(2);

    // Is relationship from source to target points to dependent primary
    // key (primary key column of destination table that is also a FK to the source
    // column)
    protected boolean toDependentPK;

    public DbRelationship() {
        super();
    }

    public DbRelationship(String name) {
        super(name);
    }

    /**
     * Prints itself as XML to the provided XMLEncoder.
     * 
     * @since 1.1
     */
    public void encodeAsXML(XMLEncoder encoder) {
        encoder.print("<db-relationship name=\"");
        encoder.print(Util.encodeXmlAttribute(getName()));
        encoder.print("\" source=\"");
        encoder.print(getSourceEntity().getName());

        if (getTargetEntityName() != null && getTargetEntity() != null) {
            encoder.print("\" target=\"");
            encoder.print(getTargetEntityName());
        }

        if (isToDependentPK() && isValidForDepPk()) {
            encoder.print("\" toDependentPK=\"true");
        }

        encoder.print("\" toMany=\"");
        encoder.print(isToMany());
        encoder.println("\">");

        encoder.indent(1);
        encoder.print(getJoins());
        encoder.indent(-1);

        encoder.println("</db-relationship>");
    }

    /**
     * Returns a target of this relationship. If relationship is not attached to a
     * DbEntity, and DbEntity doesn't have a namespace, and exception is thrown.
     */
    @Override
    public Entity getTargetEntity() {
        String targetName = getTargetEntityName();
        if (targetName == null) {
            return null;
        }

        return getNonNullNamespace().getDbEntity(targetName);
    }

    /**
     * Returns a Collection of target attributes.
     * 
     * @since 1.1
     */
    public Collection<DbAttribute> getTargetAttributes() {
        if (joins.size() == 0) {
            return Collections.EMPTY_LIST;
        }

        return CollectionUtils.collect(joins, JoinTransformers.targetExtractor);
    }

    /**
     * Returns a Collection of source attributes.
     * 
     * @since 1.1
     */
    public Collection<DbAttribute> getSourceAttributes() {
        if (joins.size() == 0) {
            return Collections.EMPTY_LIST;
        }

        return CollectionUtils.collect(joins, JoinTransformers.sourceExtractor);
    }

    /**
     * Creates a new relationship with the same set of joins, but going in the opposite
     * direction.
     * 
     * @since 1.0.5
     */
    public DbRelationship createReverseRelationship() {
        DbEntity targetEntity = (DbEntity) getTargetEntity();

        DbRelationship reverse = new DbRelationship();
        reverse.setSourceEntity(targetEntity);
        reverse.setTargetEntityName(getSourceEntity().getName());

        // TODO: andrus 12/24/2007 - one more case to handle - set reverse toDepPK = true
        // if this relationship toDepPK is false, but the entities are joined on a PK...
        // on the other hand, these can still be two independent entities...

        if (isToDependentPK()
                && !toMany
                && joins.size() == targetEntity.getPrimaryKeys().size()) {
            reverse.setToMany(false);
        }
        else {
            reverse.setToMany(!toMany);
        }

        for (DbJoin join : joins) {
            DbJoin reverseJoin = join.createReverseJoin();
            reverseJoin.setRelationship(reverse);
            reverse.addJoin(reverseJoin);
        }

        return reverse;
    }

    /**
     * Returns DbRelationship that is the opposite of this DbRelationship. This means a
     * relationship from this target entity to this source entity with the same join
     * semantics. Returns null if no such relationship exists.
     */
    public DbRelationship getReverseRelationship() {
        Entity target = this.getTargetEntity();

        if (target == null) {
            return null;
        }

        Entity src = this.getSourceEntity();

        // special case - relationship to self with no joins...
        if (target == src && joins.size() == 0) {
            return null;
        }

        TestJoin testJoin = new TestJoin(this);
        for (Relationship rel : target.getRelationships()) {
            if (rel.getTargetEntity() != src)
                continue;

            List<DbJoin> otherJoins = ((DbRelationship)rel).getJoins();
            if (otherJoins.size() != joins.size()) {
                continue;
            }

            boolean joinsMatch = true;
            for (DbJoin join : otherJoins) {
                // flip join and try to find similar
                testJoin.setSourceName(join.getTargetName());
                testJoin.setTargetName(join.getSourceName());
                if (!joins.contains(testJoin)) {
                    joinsMatch = false;
                    break;
                }
            }

            if (joinsMatch) {
                return (DbRelationship) rel;
            }
        }

        return null;
    }

    /**
     * Returns true if the relationship points to at least one of the PK columns of the
     * target entity.
     * 
     * @since 1.1
     */
    public boolean isToPK() {
        for (DbJoin join : getJoins()) {
            if (join.getTarget() == null) {
                return false;
            }

            if (join.getTarget().isPrimaryKey()) {
                return true;
            }
        }

        return false;
    }

    /**
     * Returns <code>true</code> if a method <code>isToDependentPK</code> of reverse
     * relationship of this relationship returns <code>true</code>.
     */
    public boolean isToMasterPK() {
        if (isToMany() || isToDependentPK()) {
            return false;
        }

        DbRelationship revRel = getReverseRelationship();
        return (revRel != null) ? revRel.isToDependentPK() : false;
    }

    /**
     * Returns <code>true</code> if relationship from source to target points to
     * dependent primary key. Dependent PK is a primary key column of the destination
     * table that is also a FK to the source column.
     */
    public boolean isToDependentPK() {
        return toDependentPK;
    }

    public void setToDependentPK(boolean toDependentPK) {
        if (this.toDependentPK != toDependentPK) {
            this.toDependentPK = toDependentPK;
            firePropertyDidChange();
        }
    }

    /**
     * @since 1.1
     */
    public boolean isValidForDepPk() {
        // handle case with no joins
        if (getJoins().size() == 0) {
            return false;
        }

        for (DbJoin join : getJoins()) {
            DbAttribute target = join.getTarget();
            DbAttribute source = join.getSource();

            if ((target != null && !target.isPrimaryKey())
                    || (source != null && !source.isPrimaryKey())) {
                return false;
            }
        }

        return true;
    }

    /**
     * Returns a list of joins. List is returned by reference, so any modifications of the
     * list will affect this relationship.
     */
    public List<DbJoin> getJoins() {
        return joins;
    }

    /**
     * Adds a join.
     * 
     * @since 1.1
     */
    public void addJoin(DbJoin join) {
        if (join != null) {
            joins.add(join);
        }
    }

    public void removeJoin(DbJoin join) {
        joins.remove(join);
    }

    public void removeAllJoins() {
        joins.clear();
    }

    public void setJoins(Collection<DbJoin> newJoins) {
        this.removeAllJoins();

        if (newJoins != null) {
            joins.addAll(newJoins);
        }
    }

    /**
     * Creates a snapshot of primary key attributes of a target object of this
     * relationship based on a snapshot of a source. Only "to-one" relationships are
     * supported. Returns null if relationship does not point to an object. Throws
     * CayenneRuntimeException if relationship is "to many" or if snapshot is missing id
     * components.
     */
    public Map<String, Object> targetPkSnapshotWithSrcSnapshot(Map<String, Object> srcSnapshot) {

        if (isToMany()) {
            throw new CayenneRuntimeException(
                    "Only 'to one' relationships support this method.");
        }

        Map<String, Object> idMap;

        int numJoins = joins.size();
        int foundNulls = 0;

        // optimize for the most common single column join
        if (numJoins == 1) {
            DbJoin join = joins.get(0);
            Object val = srcSnapshot.get(join.getSourceName());
            if (val == null) {
                foundNulls++;
                idMap = Collections.EMPTY_MAP;
            }
            else {
                idMap = Collections.singletonMap(join.getTargetName(), val);
            }
        }
        // handle generic case: numJoins > 1
        else {
            idMap = new HashMap<String, Object>(numJoins * 2);
            for (int i = 0; i < numJoins; i++) {
                DbJoin join = joins.get(i);
                DbAttribute source = join.getSource();
                Object val = srcSnapshot.get(join.getSourceName());

                if (val == null) {

                    // some keys may be nulls and some not in case of multi-key
                    // relationships where PK and FK partially overlap (see CAY-284)
                    if (!source.isMandatory()) {
                        return null;
                    }

                    foundNulls++;
                }
                else {
                    idMap.put(join.getTargetName(), val);
                }
            }
        }

        if (foundNulls == 0) {
            return idMap;
        }
        else if (foundNulls == numJoins) {
            return null;
        }
        else {
            throw new CayenneRuntimeException("Some parts of FK are missing in snapshot,"
                    + " relationship: "
                    + this);
        }
    }

    /**
     * Common code to srcSnapshotWithTargetSnapshot. Both are functionally the same,
     * except for the name, and whether they operate on a toMany or a toOne.
     */
    private Map<String, Object> srcSnapshotWithTargetSnapshot(Map<String, Object> targetSnapshot) {
        int len = joins.size();

        // optimize for the most common single column join
        if (len == 1) {
            DbJoin join = joins.get(0);
            Object val = targetSnapshot.get(join.getTargetName());
            return Collections.singletonMap(join.getSourceName(), val);
        }

        // general case
        Map<String, Object> idMap = new HashMap<String, Object>(len * 2);
        for (int i = 0; i < len; i++) {
            DbJoin join = joins.get(i);
            Object val = targetSnapshot.get(join.getTargetName());
            idMap.put(join.getSourceName(), val);
        }

        return idMap;
    }

    /**
     * Creates a snapshot of foreign key attributes of a source object of this
     * relationship based on a snapshot of a target. Only "to-one" relationships are
     * supported. Throws CayenneRuntimeException if relationship is "to many".
     */
    public Map<String, Object> srcFkSnapshotWithTargetSnapshot(Map<String, Object> targetSnapshot) {

        if (isToMany()) {
            throw new CayenneRuntimeException(
                    "Only 'to one' relationships support this method.");
        }

        return srcSnapshotWithTargetSnapshot(targetSnapshot);
    }

    /**
     * Creates a snapshot of primary key attributes of a source object of this
     * relationship based on a snapshot of a target. Only "to-many" relationships are
     * supported. Throws CayenneRuntimeException if relationship is "to one".
     */
    public Map<String, Object> srcPkSnapshotWithTargetSnapshot(Map<String, Object> targetSnapshot) {
        if (!isToMany())
            throw new CayenneRuntimeException(
                    "Only 'to many' relationships support this method.");
        return srcSnapshotWithTargetSnapshot(targetSnapshot);
    }

    /**
     * Sets relationship multiplicity.
     */
    public void setToMany(boolean toMany) {
        if (this.toMany != toMany) {
            this.toMany = toMany;
            this.firePropertyDidChange();
        }
    }

    protected void firePropertyDidChange() {
        RelationshipEvent event = new RelationshipEvent(this, this, this
                .getSourceEntity());
        EventManager.getDefaultManager().postEvent(event, PROPERTY_DID_CHANGE);
    }

    final static class JoinTransformers {

        static final Transformer targetExtractor = new Transformer() {

            public Object transform(Object input) {
                return (input instanceof DbJoin) ? ((DbJoin) input).getTarget() : input;
            }
        };

        static final Transformer sourceExtractor = new Transformer() {

            public Object transform(Object input) {
                return (input instanceof DbJoin) ? ((DbJoin) input).getSource() : input;
            }
        };
    }

    // a join used for comparison
    final static class TestJoin extends DbJoin {

        TestJoin(DbRelationship relationship) {
            super(relationship);
        }

        @Override
        public boolean equals(Object o) {
            if (o == null) {
                return false;
            }

            if (o == this) {
                return true;
            }

            if (!(o instanceof DbJoin)) {
                return false;
            }

            DbJoin j = (DbJoin) o;
            return j.relationship == this.relationship
                    && Util.nullSafeEquals(j.sourceName, this.sourceName)
                    && Util.nullSafeEquals(j.targetName, this.targetName);
        }
    }
}
