/**
 * Copyright (C) 2009-2013 FoundationDB, LLC
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.foundationdb.sql.optimizer.rule;

import com.foundationdb.sql.optimizer.plan.*;

import java.util.*;

/** Track which tables a conditional expression depends on that are
 * not bound from an outer context.
 * Used to determine exactly when the condition can be tested.
 */
public class ConditionDependencyAnalyzer implements PlanVisitor, ExpressionVisitor {
    private enum State { GATHER, ANALYZE };
    private State state;
    private Set<ColumnSource> upstreamTables;
    private Set<ColumnSource> referencedTables;
    private Set<ColumnExpression> referencedColumns;

    /** Make an analyzer using the upstream tables that input to the
     * given node. */
    public ConditionDependencyAnalyzer(PlanNode node) {
        upstreamTables = new HashSet<>();
        state = State.GATHER;
        node.accept(this);
    }

    /** Make an analyzer that recognizes tables from either of two sources. */
    public ConditionDependencyAnalyzer(ConditionDependencyAnalyzer a1,
                                       ConditionDependencyAnalyzer a2) {
        upstreamTables = new HashSet<>(a1.upstreamTables);
        upstreamTables.addAll(a2.upstreamTables);
    }

    /** Get the tables that are not bound by some outer contour and so
     * must be available at the point of execution. */
    public Set<ColumnSource> getUpstreamTables() {
        return upstreamTables;
    }

    /** Analyze the given condition and if it acccesses just a single
     * table, return that.  Otherwise, return <code>null</code>.
     */
    public ColumnSource analyze(ConditionExpression cond) {
        referencedTables = new HashSet<>();
        referencedColumns = new HashSet<>();
        state = State.ANALYZE;
        cond.accept(this);
        if (referencedTables.size() == 1)
            return referencedTables.iterator().next();
        else
            return null;
    }

    /** Get the tables that were referenced by the condition. */
    public Set<ColumnSource> getReferencedTables() {
        return referencedTables;
    }

    /** Get the columns that were referenced by the condition. */
    public Set<ColumnExpression> getReferencedColumns() {
        return referencedColumns;
    }

    @Override
    public boolean visitEnter(PlanNode n) {
        return visit(n);
    }

    @Override
    public boolean visitLeave(PlanNode n) {
        return true;
    }

    @Override
    public boolean visit(PlanNode n) {
        if (state == State.GATHER) {
            if (n instanceof ColumnSource)
                upstreamTables.add((ColumnSource)n);
            else if (n instanceof IndexScan)
                upstreamTables.addAll(((IndexScan)n).getTables());
        }
        return true;
    }

    @Override
    public boolean visitEnter(ExpressionNode n) {
        return visit(n);
    }

    @Override
    public boolean visitLeave(ExpressionNode n) {
        return true;
    }

    @Override
    public boolean visit(ExpressionNode n) {
        if (state == State.ANALYZE) {
            if (n instanceof ColumnExpression) {
                ColumnExpression column = (ColumnExpression)n;
                ColumnSource table = column.getTable();
                if (upstreamTables.contains(table)) {
                    referencedTables.add(table);
                    referencedColumns.add(column);
                }
            }
        }
        return true;
    }
}