jena-arq/src/main/java/org/apache/jena/sparql/algebra/optimize/VariableUsageTracker.java

/*
 * 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.sparql.algebra.optimize;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

import org.apache.jena.sparql.core.Var;

/**
 * Tracker for variable usage
 *
 */
public class VariableUsageTracker {

    private Stack<Map<String, Integer>> stack = new Stack<>();
    private Map<String, Integer> variables = new HashMap<>();

    public void push() {
        this.stack.push(this.variables);
        this.variables = new HashMap<>();
    }

    public void pop() {
        if (this.stack.size() == 0)
            throw new IllegalStateException("Stack is empty");
        this.variables = this.stack.pop();
    }

    public void increment(Collection<Var> vars) {
        for (Var var : vars) {
            increment(var);
        }
    }

    public void increment(String var) {
        if (!variables.containsKey(var)) {
            variables.put(var, 1);
        } else {
            variables.put(var, variables.get(var) + 1);
        }
    }

    public void increment(Var var) {
        increment(var.getName());
    }

    public void decrement(Collection<Var> vars) {
        for (Var var : vars) {
            decrement(var);
        }
    }

    public void decrement(String var) {
        if (variables.containsKey(var)) {
            variables.put(var, variables.get(var) - 1);
            if (variables.get(var) <= 0)
                variables.remove(var);
        }
    }

    public void decrement(Var var) {
        decrement(var.getName());
    }

    public int getUsageCount(String var) {
        Integer i = variables.get(var);
        return i != null ? i.intValue() : 0;
    }

    public int getUsageCount(Var var) {
        return getUsageCount(var.getName());
    }
}