/*
 * 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.jasper.compiler;

import org.apache.jasper.JasperException;
import org.apache.jasper.Options;
import org.apache.jasper.TrimSpacesOption;

/**
 * Provides optimizations for text nodes in JSP pages.
 */
public class TextOptimizer {

    /**
     * Constructs a new TextOptimizer. This utility class should not be instantiated.
     */
    public TextOptimizer() {
    }

    /**
     * A visitor to concatenate contiguous template texts.
     */
    private static class TextCatVisitor extends Node.Visitor {

        private static final String EMPTY_TEXT = "";
        private static final String SINGLE_SPACE = " ";

        private final Options options;
        private final PageInfo pageInfo;
        private int textNodeCount = 0;
        private Node.TemplateText firstTextNode = null;
        private StringBuilder textBuffer;

        TextCatVisitor(Compiler compiler) {
            options = compiler.getCompilationContext().getOptions();
            pageInfo = compiler.getPageInfo();
        }

        @Override
        public void doVisit(Node n) throws JasperException {
            collectText();
        }

        /*
         * The following directives are ignored in text concatenation
         */

        @Override
        public void visit(Node.PageDirective n) throws JasperException {
        }

        @Override
        public void visit(Node.TagDirective n) throws JasperException {
        }

        @Override
        public void visit(Node.TaglibDirective n) throws JasperException {
        }

        @Override
        public void visit(Node.AttributeDirective n) throws JasperException {
        }

        @Override
        public void visit(Node.VariableDirective n) throws JasperException {
        }

        /*
         * Don't concatenate text across body boundaries
         */
        @Override
        public void visitBody(Node n) throws JasperException {
            super.visitBody(n);
            collectText();
        }

        @Override
        public void visit(Node.TemplateText n) throws JasperException {
            if (n.isAllSpace()) {
                if ((options.getTrimSpaces() == TrimSpacesOption.TRUE || pageInfo.isTrimDirectiveWhitespaces())) {
                    n.setText(EMPTY_TEXT);
                    return;
                } else if (options.getTrimSpaces() == TrimSpacesOption.SINGLE) {
                    n.setText(SINGLE_SPACE);
                    return;
                }
            }

            if (textNodeCount++ == 0) {
                firstTextNode = n;
                textBuffer = new StringBuilder(n.getText());
            } else {
                // Append text to text buffer
                textBuffer.append(n.getText());
                n.setText(EMPTY_TEXT);
            }
        }

        /**
         * This method breaks concatenation mode. As a side effect it copies the concatenated string to the first text
         * node
         */
        private void collectText() {

            if (textNodeCount > 1) {
                // Copy the text in buffer into the first template text node.
                firstTextNode.setText(textBuffer.toString());
            }
            textNodeCount = 0;
        }

    }

    /**
     * Concatenates contiguous text nodes in the given page to reduce the number of
     * write operations in the generated servlet code.
     *
     * @param compiler the JSP compiler
     * @param page the page node tree
     * @throws JasperException if an error occurs during optimization
     */
    public static void concatenate(Compiler compiler, Node.Nodes page) throws JasperException {

        TextCatVisitor v = new TextCatVisitor(compiler);
        page.visit(v);

        // Cleanup, in case the page ends with a template text
        v.collectText();
    }
}