/*
 * 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.jena.tdb2.solver;

import java.util.*;

import org.apache.jena.atlas.logging.Log;
import org.apache.jena.graph.Node;
import org.apache.jena.riot.out.NodeFmtLib;
import org.apache.jena.sparql.core.Var;
import org.apache.jena.sparql.engine.binding.Binding;
import org.apache.jena.sparql.engine.binding.BindingBase;
import org.apache.jena.tdb2.TDBException;
import org.apache.jena.tdb2.store.NodeId;
import org.apache.jena.tdb2.store.nodetable.NodeTable;

/** Bind that delays turning a NodeId into a Node until explicitly needed by get() */

public class BindingTDB extends BindingBase
{
    private final NodeTable nodeTable;
    private final BindingNodeId idBinding;

    private static final boolean caching = false;
    // Whether the cache is worthwhile is unclear - the NodeTable keeps a cache.
    private final Map<Var,Node> cache = ( caching ? new HashMap<>() : null );

    public BindingTDB(BindingNodeId idBinding, NodeTable nodeTable)
    {
        // BindingNodeId contains the bindings actually used  copied down when created.
        super(idBinding.getParentBinding());
        this.idBinding = idBinding;
        this.nodeTable = nodeTable;
    }

    @Override
    protected int size1() { return idBinding.size(); }

    private List<Var> vars = null;

    /** Iterate over all the names of variables. */
    @Override
    protected Iterator<Var> vars1()
    {
        if ( vars == null )
            vars = calcVars();
        return vars.iterator();
    }

    private List<Var> calcVars()
    {
        List<Var> vars = new ArrayList<>(4);
        // Only if not in parent.
        // A (var/value) binding may have been copied down to record it's NodeId.

        Binding b = idBinding.getParentBinding();

        Iterator<Var> iter = idBinding.iterator();
        for ( Var v : idBinding )
        {
            if ( b == null || ! b.contains(v) )
                vars.add(v);
        }
        return vars;
    }

    @Override
    protected boolean isEmpty1()
    {
        return size1() == 0;
    }

    @Override
    public boolean contains1(Var var)
    {
        return idBinding.containsKey(var);
    }

    public BindingNodeId getBindingId() { return idBinding; }

    public NodeId getNodeId(Var var)
    {
        NodeId id = idBinding.get(var);
        if ( id != null )
            return id;
        // In case we are handling known missing nodes.
        if ( NodeId.isDoesNotExist(id) )
            return null;

        if ( parent == null )
            return null;
        if ( parent instanceof BindingTDB )
            return ((BindingTDB)parent).getNodeId(var);
        return null;
    }

    @Override
    public Node get1(Var var)
    {
        try {
            Node n = cacheGet(var);
            if ( n != null )
                return n;

            NodeId id = idBinding.get(var);
            if ( id == null )
                return null;
            if ( NodeId.isDoesNotExist(id) )
                return null;
            n = nodeTable.getNodeForNodeId(id);
            if ( n == null )
                // But there was to put it in the BindingNodeId.
                throw new TDBException("No node in NodeTable for NodeId "+id);
            // Update cache.
            cachePut(var, n);
            return n;
        } catch (Exception ex)
        {
            Log.error(this, String.format("get1(%s)", var), ex);
            return null;
        }
    }

    private void cachePut(Var var, Node n)
    {
        if ( cache != null ) cache.put(var, n);
    }

    private Node cacheGet(Var var)
    {
        if ( cache == null ) return null;
        return cache.get(var);
    }

    @Override
    protected void fmtVar(StringBuffer sbuff, Var var)
    {
        NodeId id = idBinding.get(var);
        String extra = "";
        if ( id != null )
            extra = "/"+id;
        Node node = get(var);
        String tmp = NodeFmtLib.displayStr(node);
        sbuff.append("( ?"+var.getVarName()+extra+" = "+tmp+" )");
    }
}
