/*
 * 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.regexp;

import java.io.Reader;
import java.io.IOException;

/**
 * Encapsulates java.io.Reader as CharacterIterator
 *
 * @author <a href="mailto:ales.novak@netbeans.com">Ales Novak</a>
 * @version CVS $Id: ReaderCharacterIterator.java 518156 2007-03-14 14:31:26Z vgritsenko $
 */
public final class ReaderCharacterIterator implements CharacterIterator
{
    /** Underlying reader */
    private final Reader reader;

    /** Buffer of read chars */
    private final StringBuffer buff;

    /** read end? */
    private boolean closed;

    /** @param reader a Reader, which is parsed */
    public ReaderCharacterIterator(Reader reader)
    {
        this.reader = reader;
        this.buff = new StringBuffer(512);
        this.closed = false;
    }

    /** @return a substring */
    public String substring(int beginIndex, int endIndex)
    {
        try
        {
            ensure(endIndex);
            return buff.toString().substring(beginIndex, endIndex);
        }
        catch (IOException e)
        {
            throw new StringIndexOutOfBoundsException(e.getMessage());
        }
    }

    /** @return a substring */
    public String substring(int beginIndex)
    {
        try
        {
            readAll();
            return buff.toString().substring(beginIndex);
        }
        catch (IOException e)
        {
            throw new StringIndexOutOfBoundsException(e.getMessage());
        }
    }

    /** @return a character at the specified position. */
    public char charAt(int pos)
    {
        try
        {
            ensure(pos);
            return buff.charAt(pos);
        }
        catch (IOException e)
        {
            throw new StringIndexOutOfBoundsException(e.getMessage());
        }
    }

    /** @return <tt>true</tt> iff if the specified index is after the end of the character stream */
    public boolean isEnd(int pos)
    {
        if (buff.length() > pos)
        {
            return false;
        }
        else
        {
            try
            {
                ensure(pos);
                return (buff.length() <= pos);
            }
            catch (IOException e)
            {
                throw new StringIndexOutOfBoundsException(e.getMessage());
            }
        }
    }

    /** Reads n characters from the stream and appends them to the buffer */
    private int read(int n) throws IOException
    {
        if (closed)
        {
            return 0;
        }

        char[] c = new char[n];
        int count = 0;
        int read = 0;

        do
        {
            read = reader.read(c);
            if (read < 0) // EOF
            {
                closed = true;
                break;
            }
            count += read;
            buff.append(c, 0, read);
        }
        while (count < n);

        return count;
    }

    /** Reads rest of the stream. */
    private void readAll() throws IOException
    {
        while(! closed)
        {
            read(1000);
        }
    }

    /** Reads chars up to the idx */
    private void ensure(int idx) throws IOException
    {
        if (closed)
        {
            return;
        }

        if (idx < buff.length())
        {
            return;
        }
        read(idx + 1 - buff.length());
    }
}
