src/main/java/org/apache/sling/scripting/sightly/compiler/util/VariableTracker.java

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 * 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.
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package org.apache.sling.scripting.sightly.compiler.util;

import java.util.AbstractMap;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Stack;

/**
 * Tracks information related to HTL variables, at different levels of the compiler.
 */
public final class VariableTracker<T> {

    private final Map<String, Stack<T>> variableData = new HashMap<>();
    private final Stack<String> declarationStack = new Stack<>();

    /**
     * Checks if the variable identified by {@code name} is tracked by this tracker or not.
     *
     * @param name the name of the variable
     * @return {@code true} if the variable is declared, {@code false} otherwise
     */
    public boolean isDeclared(String name) {
        name = name.toLowerCase();
        Stack<T> dataStack = variableData.get(name);
        return dataStack != null;
    }

    /**
     * Pushes a variable to this tracker. Call this method whenever a variable is declared.
     *
     * @param name the name of the variable
     * @param data the data associated with the variable
     */
    public void pushVariable(String name, T data) {
        if (name != null) {
            name = name.toLowerCase();
            Stack<T> dataStack = variableData.get(name);
            if (dataStack == null) {
                dataStack = new Stack<>();
                variableData.put(name, dataStack);
            }
            dataStack.push(data);
            declarationStack.push(name);
        }
    }

    /**
     * Pops a variable from this tracker. Call this method whenever a variable goes out of scope.
     *
     * @return the name of the popped variable
     * @throws java.util.NoSuchElementException if there are no declared variables in the scope
     */
    public String popVariable() {
        String variable = declarationStack.pop();
        Stack<T> dataStack = variableData.get(variable);
        assert dataStack != null;
        dataStack.pop();
        if (dataStack.isEmpty()) {
            variableData.remove(variable);
        }
        return variable;
    }

    /**
     * Peeks at the top of the declaration stack.
     *
     * @return the most recently declared variable and its associated data
     * @throws java.util.NoSuchElementException if there are no variables in scope
     */
    public Map.Entry<String, T> peek() {
        String variable = declarationStack.peek();
        Stack<T> dataStack = variableData.get(variable);
        assert dataStack != null;
        T data = dataStack.peek();
        return new AbstractMap.SimpleImmutableEntry<>(variable, data);
    }

    /**
     * Checks if the declaration stack is empty.
     *
     * @return {@code true} if the stack is empty, {@code false} otherwise
     */
    public boolean isEmpty() {
        return declarationStack.isEmpty();
    }

    /**
     * Get the data associated with the given variable.
     *
     * @param name the name of the variable
     * @return the associated data or {@code null} if that variable is not in scope
     */
    public T get(String name) {
        name = name.toLowerCase();
        Stack<T> dataStack = variableData.get(name);
        if (dataStack == null) {
            return null;
        }
        assert !dataStack.isEmpty();
        return dataStack.peek();
    }

    /**
     * Check whether a variable was declared and is visible in the current scope.
     *
     * @param name the name of the variable
     * @return {@code true} if the variable is visible in the current scope, {@code false} otherwise
     */
    public boolean isInScope(String name) {
        name = name.toLowerCase();
        return variableData.get(name) != null;
    }

    /**
     * Get an immutable view of all the data items associated with the specified variable.
     *
     * @param name the name of the variable
     * @return a list of all the data associated with this variable name. If the variable is not declared in the current scope then that
     * list will be empty. Otherwise it will contain all the data associated for the current scope starting with the data associated at
     * the topmost scope and ending with the most recently associated data
     */
    public List<T> getAll(String name) {
        name = name.toLowerCase();
        Stack<T> dataStack = variableData.get(name);
        if (dataStack == null) {
            return Collections.emptyList();
        }
        return Collections.unmodifiableList(dataStack);
    }

    /**
     * Get how many times a variable was declared in the current scope.
     *
     * @param name the name of the variable
     * @return the number of declarations for a variable in the current scope
     */
    public int getOccurrenceCount(String name) {
        name = name.toLowerCase();
        Stack<T> dataStack = variableData.get(name);
        if (dataStack == null) {
            return 0;
        }
        return dataStack.size();
    }
}