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/*
 * Copyright (c) 2002-2015 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.kernel;

import java.util.Iterator;
import java.util.LinkedList;

import org.neo4j.graphdb.Node;
import org.neo4j.graphdb.Path;
import org.neo4j.graphdb.PropertyContainer;
import org.neo4j.graphdb.Relationship;
import org.neo4j.graphdb.traversal.Paths;
import org.neo4j.graphdb.traversal.TraversalBranch;

public class BidirectionalTraversalBranchPath implements Path
{
    private final TraversalBranch start;
    private final TraversalBranch end;
    private final Node endNode;
    private final Relationship lastRelationship;
    
    private Node cachedStartNode;
    private LinkedList cachedRelationships;

    public BidirectionalTraversalBranchPath( TraversalBranch start, TraversalBranch end )
    {
        this.start = start;
        this.end = end;
        
        // Most used properties: endNode and lastRelationship, so cache them right away (semi-expensive though).
        Iterator endPathEntities = end.iterator();
        this.endNode = (Node) endPathEntities.next();
        this.lastRelationship = endPathEntities.hasNext() ?
                (Relationship) endPathEntities.next() : start.lastRelationship();
    }

    @Override
    public Node startNode()
    {
        // Getting the start node is expensive in some Path implementations, so cache it
        if ( cachedStartNode == null )
            cachedStartNode = start.startNode();
        return cachedStartNode;
    }

    @Override
    public Node endNode()
    {
        return this.endNode;
    }

    @Override
    public Relationship lastRelationship()
    {
        return this.lastRelationship;
    }

    @Override
    public Iterable relationships()
    {
        // Cache the relationships since we use them in hashCode/equals too.
        if ( cachedRelationships == null )
            cachedRelationships = gatherRelationships( start, end );
        return cachedRelationships;
    }

    @Override
    public Iterable reverseRelationships()
    {
        return gatherRelationships( end, start );
    }
    
    private LinkedList gatherRelationships( TraversalBranch first, TraversalBranch then )
    {
        // TODO Don't loop through them all up front
        LinkedList relationships = new LinkedList();
        TraversalBranch branch = first;
        while ( branch.length() > 0 )
        {
            relationships.addFirst( branch.lastRelationship() );
            branch = branch.parent();
        }
        // We can might as well cache start node since we're right now there anyway
        if ( cachedStartNode == null && first == start )
            cachedStartNode = branch.endNode();
        branch = then;
        while ( branch.length() > 0 )
        {
            relationships.add( branch.lastRelationship() );
            branch = branch.parent();
        }
        if ( cachedStartNode == null && then == start )
            cachedStartNode = branch.endNode();
        return relationships;
    }
    
    @Override
    public Iterable nodes()
    {
        return gatherNodes( start, end );
    }

    @Override
    public Iterable reverseNodes()
    {
        return gatherNodes( end, start );
    }

    private Iterable gatherNodes( TraversalBranch first, TraversalBranch then )
    {
        // TODO Don't loop through them all up front
        LinkedList nodes = new LinkedList();
        TraversalBranch branch = first;
        while ( branch.length() > 0 )
        {
            nodes.addFirst( branch.endNode() );
            branch = branch.parent();
        }
        if ( cachedStartNode == null && first == start )
            cachedStartNode = branch.endNode();
        nodes.addFirst( branch.endNode() );
        branch = then.parent();
        if ( branch != null )
        {
            while ( branch.length() > 0 )
            {
                nodes.add( branch.endNode() );
                branch = branch.parent();
            }
            if ( branch.length() >= 0 )
            {
                nodes.add( branch.endNode() );
            }
        }
        if ( cachedStartNode == null && then == start )
            cachedStartNode = branch.endNode();
        return nodes;
    }
    
    @Override
    public int length()
    {
        return start.length() + end.length();
    }

    @Override
    public Iterator iterator()
    {
        // TODO Don't loop through them all up front
        LinkedList entities = new LinkedList();
        TraversalBranch branch = start;
        while ( branch.length() > 0 )
        {
            entities.addFirst( branch.endNode() );
            entities.addFirst( branch.lastRelationship() );
            branch = branch.parent();
        }
        entities.addFirst( branch.endNode() );
        if ( cachedStartNode == null )
            cachedStartNode = branch.endNode();
        if ( end.length() > 0 )
        {
            entities.add( end.lastRelationship() );
            branch = end.parent();
            while ( branch.length() > 0 )
            {
                entities.add( branch.endNode() );
                entities.add( branch.lastRelationship() );
                branch = branch.parent();
            }
            entities.add( branch.endNode() );
        }
        return entities.iterator();
    }
    
    @Override
    public int hashCode()
    {
        return relationships().hashCode();
    }
    
    @Override
    public boolean equals( Object obj )
    {
        if ( obj == this )
            return true;
        if ( !( obj instanceof Path ) )
            return false;
        
        Path other = (Path) obj;
        return relationships().equals( other.relationships() ) && other.startNode().equals( cachedStartNode );
    }
    
    @Override
    public String toString()
    {
        return Paths.defaultPathToString( this );
    }
}