/*
 * Copyright (c) 1997, 2020 Oracle and/or its affiliates and others.
 * All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 jakarta.servlet.jsp.el;

/**
 * <p>
 * The abstract base class for an expression-language evaluator. Classes that implement an expression language expose
 * their functionality via this abstract class.
 * </p>
 *
 * <p>
 * An instance of the ExpressionEvaluator can be obtained via the JspContext / PageContext
 * </p>
 *
 * <p>
 * The parseExpression() and evaluate() methods must be thread-safe. That is, multiple threads may call these methods on
 * the same ExpressionEvaluator object simultaneously. Implementations should synchronize access if they depend on
 * transient state. Implementations should not, however, assume that only one object of each ExpressionEvaluator type
 * will be instantiated; global caching should therefore be static.
 * </p>
 *
 * <p>
 * Only a single EL expression, starting with '${' and ending with '}', can be parsed or evaluated at a time. EL
 * expressions cannot be mixed with static text. For example, attempting to parse or evaluate
 * "<code>abc${1+1}def${1+1}ghi</code>" or even "<code>${1+1}${1+1}</code>" will cause an <code>ELException</code> to be
 * thrown.
 * </p>
 *
 * <p>
 * The following are examples of syntactically legal EL expressions:
 * </p>
 *
 * <ul>
 * <li><code>${person.lastName}</code></li>
 * <li><code>${8 * 8}</code></li>
 * <li><code>${my:reverse('hello')}</code></li>
 * </ul>
 *
 * @deprecated As of JSP 2.1, replaced by {@link jakarta.el.ExpressionFactory}
 * @since JSP 2.0
 */
@Deprecated
public abstract class ExpressionEvaluator {

    /**
     * Prepare an expression for later evaluation. This method should perform syntactic validation of the expression; if
     * in doing so it detects errors, it should raise an ELParseException.
     *
     * @param expression   The expression to be evaluated.
     * @param expectedType The expected type of the result of the evaluation
     * @param fMapper      A FunctionMapper to resolve functions found in the expression. It can be null, in which case
     *                     no functions are supported for this invocation. The ExpressionEvaluator must not hold on to
     *                     the FunctionMapper reference after returning from <code>parseExpression()</code>. The
     *                     <code>Expression</code> object returned must invoke the same functions regardless of whether
     *                     the mappings in the provided <code>FunctionMapper</code> instance change between calling
     *                     <code>ExpressionEvaluator.parseExpression()</code> and <code>Expression.evaluate()</code>.
     * @return The Expression object encapsulating the arguments.
     *
     * @exception ELException Thrown if parsing errors were found.
     */
    public abstract Expression parseExpression(String expression, Class<?> expectedType, FunctionMapper fMapper)
            throws ELException;

    /**
     * Evaluates an expression. This method may perform some syntactic validation and, if so, it should raise an
     * ELParseException error if it encounters syntactic errors. EL evaluation errors should cause an ELException to be
     * raised.
     *
     * @param expression   The expression to be evaluated.
     * @param expectedType The expected type of the result of the evaluation
     * @param vResolver    A VariableResolver instance that can be used at runtime to resolve the name of implicit
     *                     objects into Objects.
     * @param fMapper      A FunctionMapper to resolve functions found in the expression. It can be null, in which case
     *                     no functions are supported for this invocation.
     * @return The result of the expression evaluation.
     *
     * @exception ELException Thrown if the expression evaluation failed.
     */
    public abstract Object evaluate(String expression, Class<?> expectedType, VariableResolver vResolver,
            FunctionMapper fMapper) throws ELException;
}
