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/**
 * Copyright (C) 2015 The Gravitee team (http://gravitee.io)
 *
 * 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 io.gravitee.el.spel;

import io.gravitee.node.api.cache.Cache;
import io.gravitee.node.api.cache.CacheConfiguration;
import io.gravitee.node.cache.standalone.StandaloneCache;
import java.util.regex.Pattern;
import org.springframework.expression.Expression;
import org.springframework.expression.ParserContext;
import org.springframework.expression.spel.SpelCompilerMode;
import org.springframework.expression.spel.SpelParserConfiguration;

/**
 * @author Jeoffrey HAEYAERT (jeoffrey.haeyaert at graviteesource.com)
 * @author GraviteeSource Team
 */
public class SpelExpressionParser {

    private static final String EXPRESSION_PREFIX = "{";
    private static final String EXPRESSION_SUFFIX = "}";
    private static final String EXPRESSION_REGEX = "\\" + EXPRESSION_PREFIX + "(\\s*[^#T\\(\\s])";
    private static final Pattern EXPRESSION_REGEX_PATTERN = Pattern.compile(EXPRESSION_REGEX);
    private static final String EXPRESSION_REGEX_SUBSTITUTE = EXPRESSION_PREFIX + "'" + EXPRESSION_PREFIX + "'" + EXPRESSION_SUFFIX + "$1";
    private static final ParserContext PARSER_CONTEXT = new TemplateParserContext(EXPRESSION_PREFIX, EXPRESSION_SUFFIX);
    private static final org.springframework.expression.spel.standard.SpelExpressionParser EXPRESSION_PARSER = new org.springframework.expression.spel.standard.SpelExpressionParser(
        new SpelParserConfiguration(SpelCompilerMode.MIXED, null)
    );

    protected static final Cache expressions;

    private static final int CACHE_EXPRESSION_MAX_SIZE = 20000;
    private static final int CACHE_EXPRESSION_IDLE_SECONDS = 3600;

    static {
        final CacheConfiguration cacheConfiguration = new CacheConfiguration();
        cacheConfiguration.setMaxSize(CACHE_EXPRESSION_MAX_SIZE);
        cacheConfiguration.setTimeToIdleSeconds(CACHE_EXPRESSION_IDLE_SECONDS);

        expressions = new StandaloneCache<>("el", cacheConfiguration);
    }

    public CachedExpression parseAndCacheExpression(String expression) {
        CachedExpression exp = expressions.get(expression);
        if (exp != null) {
            return exp;
        }

        exp = new CachedExpression(parseExpression(expression));
        expressions.put(expression, exp);

        return exp;
    }

    public Expression parseExpression(String expression) {
        return EXPRESSION_PARSER.parseExpression(
            EXPRESSION_REGEX_PATTERN.matcher(expression).replaceAll(EXPRESSION_REGEX_SUBSTITUTE),
            PARSER_CONTEXT
        );
    }
}