/*
 *  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.directory.server.xdbm.search.impl;


import java.util.List;
import java.util.ArrayList;

import org.apache.directory.server.xdbm.Store;
import org.apache.directory.server.xdbm.IndexCursor;
import org.apache.directory.server.xdbm.search.Evaluator;
import org.apache.directory.server.core.entry.ServerEntry;
import org.apache.directory.shared.ldap.NotImplementedException;
import org.apache.directory.shared.ldap.filter.*;


/**
 * Builds Cursors over candidates that satisfy a filter expression.
 * 
 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
 * @version $Rev$
 */
public class CursorBuilder
{
    /** The database used by this builder */
    private Store<ServerEntry> db = null;

    /** Evaluator dependency on a EvaluatorBuilder */
    private EvaluatorBuilder evaluatorBuilder;


    /**
     * Creates an expression tree enumerator.
     *
     * @param db database used by this enumerator
     * @param evaluatorBuilder the evaluator builder
     */
    public CursorBuilder( Store<ServerEntry> db, EvaluatorBuilder evaluatorBuilder )
    {
        this.db = db;
        this.evaluatorBuilder = evaluatorBuilder;
    }


    public IndexCursor<?,ServerEntry> build( ExprNode node ) throws Exception
    {
        switch ( node.getAssertionType() )
        {
            /* ---------- LEAF NODE HANDLING ---------- */

            case APPROXIMATE:
                return new ApproximateCursor( db, ( ApproximateEvaluator ) evaluatorBuilder.build( node ) );
            case EQUALITY:
                return new EqualityCursor( db, ( EqualityEvaluator ) evaluatorBuilder.build( node ) );
            case GREATEREQ:
                return new GreaterEqCursor( db, ( GreaterEqEvaluator ) evaluatorBuilder.build( node ) );
            case LESSEQ:
                return new LessEqCursor( db, ( LessEqEvaluator ) evaluatorBuilder.build( node ) );
            case PRESENCE:
                return new PresenceCursor( db, ( PresenceEvaluator ) evaluatorBuilder.build( node ) );
            case SCOPE:
                if ( ( ( ScopeNode ) node ).getScope() == SearchScope.ONELEVEL )
                {
                    return new OneLevelScopeCursor( db, ( OneLevelScopeEvaluator ) evaluatorBuilder.build( node ) );
                }
                else
                {
                    return new SubtreeScopeCursor( db, ( SubtreeScopeEvaluator ) evaluatorBuilder.build( node ) );
                }
            case SUBSTRING:
                return new SubstringCursor( db, ( SubstringEvaluator ) evaluatorBuilder.build( node ) );

            /* ---------- LOGICAL OPERATORS ---------- */

            case AND:
                return buildAndCursor( ( AndNode ) node );
            case NOT:
                return new NotCursor( db, evaluatorBuilder.build( ( ( NotNode ) node).getFirstChild() ) );
            case OR:
                return buildOrCursor( ( OrNode ) node );

            /* ----------  NOT IMPLEMENTED  ---------- */

            case ASSERTION:
            case EXTENSIBLE:
                throw new NotImplementedException();

            default:
                throw new IllegalStateException( "Unknown assertion type: " + node.getAssertionType() );
        }
    }


    /**
     * Creates a OrCursor over a disjunction expression branch node.
     *
     * @param node the disjunction expression branch node
     * @return Cursor over candidates satisfying disjunction expression
     * @throws Exception on db access failures
     */
    private IndexCursor<?,ServerEntry> buildOrCursor( OrNode node ) throws Exception
    {
        List<ExprNode> children = node.getChildren();
        List<IndexCursor<?,ServerEntry>> childCursors = new ArrayList<IndexCursor<?,ServerEntry>>( children.size() );
        List<Evaluator<? extends ExprNode, ServerEntry>> childEvaluators
            = new ArrayList<Evaluator<? extends ExprNode, ServerEntry>>( children.size() );

        // Recursively create Cursors and Evaluators for each child expression node
        for ( ExprNode child : children )
        {
            childCursors.add( build( child ) );
            childEvaluators.add( evaluatorBuilder.build( child ) );
        }

        //noinspection unchecked
        return new OrCursor( childCursors, childEvaluators );
    }


    /**
     * Creates an AndCursor over a conjunction expression branch node.
     *
     * @param node a conjunction expression branch node
     * @return Cursor over the conjunction expression
     * @throws Exception on db access failures
     */
    private IndexCursor<?,ServerEntry> buildAndCursor( AndNode node ) throws Exception
    {
        int minIndex = 0;
        long minValue = Long.MAX_VALUE;
        //noinspection UnusedAssignment
        long value = Long.MAX_VALUE;

        /*
         * We scan the child nodes of a branch node searching for the child
         * expression node with the smallest scan count.  This is the child
         * we will use for iteration by creating a Cursor over its expression.
         */
        final List<ExprNode> children = node.getChildren();
        
        for ( int ii = 0; ii < children.size(); ii++ )
        {
            ExprNode child = children.get( ii );
            Object count = child.get( "count" );
            if( count == null )
            {
                continue;
            }
            value = ( Long ) count;
            minValue = Math.min( minValue, value );

            if ( minValue == value )
            {
                minIndex = ii;
            }
        }

        // Once found we build the child Evaluators minus the one for the minChild
        ExprNode minChild = children.get( minIndex );
        List<Evaluator<? extends ExprNode, ServerEntry>> childEvaluators =
            new ArrayList<Evaluator<? extends ExprNode, ServerEntry>>( children.size() - 1 );
        for ( ExprNode child : children )
        {
            if ( child == minChild )
            {
                continue;
            }

            childEvaluators.add( evaluatorBuilder.build( child ) );
        }

        // Do recursive call to build min child Cursor then create AndCursor
        IndexCursor<?,ServerEntry> childCursor = build( minChild );
        return new AndCursor( childCursor, childEvaluators );
    }
}