/*
 * 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.any23.extractor.html;

import java.io.IOException;
import java.io.InputStream;

/**
 * Extension of {@link java.io.InputStream} meant to detect and replace any occurrence of inline <i>span</i>:
 *
 * <pre>
 * &lt;span/&gt;
 * </pre>
 *
 * with an open close tag sequence:
 *
 * <pre>
 * &lt;span&gt;&lt;/span&gt;
 * </pre>
 *
 * @author Michele Mostarda (mostarda@fbk.eu)
 */
public class SpanCloserInputStream extends InputStream {

    private static final String TRAILING_SEQUENCE_OPEN = "<span";
    private static final char TRAILING_SEQUENCE_CLOSE = '>';
    private static final String CLOSE_SEQUENCE = "</span>";

    private final InputStream wrapped;

    private int trailingSequenceOpenMatch = 0;
    private int closeSequenceIndex = 0;
    private boolean trailingSequenceOpenDetected = false;
    private boolean trailingSequenceCloseDetected = false;
    private boolean inlineDetected = false;
    private boolean betweenQuotes = false;

    public SpanCloserInputStream(InputStream is) {
        wrapped = is;
    }

    @Override
    public int read() throws IOException {
        if (trailingSequenceOpenDetected && inlineDetected && trailingSequenceCloseDetected) {
            final int ret = CLOSE_SEQUENCE.charAt(closeSequenceIndex);
            closeSequenceIndex++;
            if (closeSequenceIndex >= CLOSE_SEQUENCE.length()) {
                resetDetector();
            }
            return ret;
        } else if (trailingSequenceOpenDetected && trailingSequenceCloseDetected) {
            resetDetector();
        }

        int c = wrapped.read();
        if (c == '"') {
            betweenQuotes = !betweenQuotes;
        } else if (c == '/' && !betweenQuotes && trailingSequenceOpenDetected && !trailingSequenceCloseDetected) {
            inlineDetected = true;
            c = wrapped.read();
        }

        if (!trailingSequenceOpenDetected && checkOpenTrailingSequence(c)) {
            trailingSequenceOpenDetected = true;
            trailingSequenceCloseDetected = false;
        } else if (c == TRAILING_SEQUENCE_CLOSE && trailingSequenceOpenDetected) {
            trailingSequenceCloseDetected = true;
        }
        return c;
    }

    private boolean checkOpenTrailingSequence(int c) {
        if (TRAILING_SEQUENCE_OPEN.charAt(trailingSequenceOpenMatch) == Character.toLowerCase(c)) {
            trailingSequenceOpenMatch++;
            if (trailingSequenceOpenMatch == TRAILING_SEQUENCE_OPEN.length()) {
                trailingSequenceOpenMatch = 0;
                return true;
            }
        } else {
            trailingSequenceOpenMatch = 0;
        }
        return false;
    }

    private void resetDetector() {
        trailingSequenceOpenMatch = 0;
        closeSequenceIndex = 0;
        trailingSequenceOpenDetected = false;
        trailingSequenceCloseDetected = false;
        inlineDetected = false;
        betweenQuotes = false;
    }

}
