package org.codehaus.plexus.util.xml;

/*
 * Copyright The Codehaus 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.
 */

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.StringWriter;
import java.io.Writer;
import java.nio.file.Files;
import java.util.Locale;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Character stream that handles (or at least attempts to) all the necessary Voodo to figure out the charset encoding of
 * the XML document written to the stream.
 * 
 * @author <a href="mailto:hboutemy@codehaus.org">Herve Boutemy</a>
 *
 * @since 1.4.4
 */
public class XmlStreamWriter
    extends Writer
{
    private static final int BUFFER_SIZE = 4096;

    private StringWriter xmlPrologWriter = new StringWriter( BUFFER_SIZE );

    private OutputStream out;

    private Writer writer;

    private String encoding;

    public XmlStreamWriter( OutputStream out )
    {
        this.out = out;
    }

    public XmlStreamWriter( File file )
        throws IOException
    {
        this( Files.newOutputStream( file.toPath() ) );
    }

    public String getEncoding()
    {
        return encoding;
    }

    @Override
    public void close()
        throws IOException
    {
        if ( writer == null )
        {
            encoding = "UTF-8";
            writer = new OutputStreamWriter( out, encoding );
            writer.write( xmlPrologWriter.toString() );
        }
        writer.close();
    }

    @Override
    public void flush()
        throws IOException
    {
        if ( writer != null )
        {
            writer.flush();
        }
    }

    private void detectEncoding( char[] cbuf, int off, int len )
        throws IOException
    {
        int size = len;
        StringBuffer xmlProlog = xmlPrologWriter.getBuffer();
        if ( xmlProlog.length() + len > BUFFER_SIZE )
        {
            size = BUFFER_SIZE - xmlProlog.length();
        }
        xmlPrologWriter.write( cbuf, off, size );

        // try to determine encoding
        if ( xmlProlog.length() >= 5 )
        {
            if ( xmlProlog.substring( 0, 5 ).equals( "<?xml" ) )
            {
                // try to extract encoding from XML prolog
                int xmlPrologEnd = xmlProlog.indexOf( "?>" );
                if ( xmlPrologEnd > 0 )
                {
                    // ok, full XML prolog written: let's extract encoding
                    Matcher m = ENCODING_PATTERN.matcher( xmlProlog.substring( 0, xmlPrologEnd ) );
                    if ( m.find() )
                    {
                        encoding = m.group( 1 ).toUpperCase( Locale.ENGLISH );
                        encoding = encoding.substring( 1, encoding.length() - 1 );
                    }
                    else
                    {
                        // no encoding found in XML prolog: using default encoding
                        encoding = "UTF-8";
                    }
                }
                else
                {
                    if ( xmlProlog.length() >= BUFFER_SIZE )
                    {
                        // no encoding found in first characters: using default encoding
                        encoding = "UTF-8";
                    }
                }
            }
            else
            {
                // no XML prolog: using default encoding
                encoding = "UTF-8";
            }
            if ( encoding != null )
            {
                // encoding has been chosen: let's do it
                xmlPrologWriter = null;
                writer = new OutputStreamWriter( out, encoding );
                writer.write( xmlProlog.toString() );
                if ( len > size )
                {
                    writer.write( cbuf, off + size, len - size );
                }
            }
        }
    }

    @Override
    public void write( char[] cbuf, int off, int len )
        throws IOException
    {
        if ( xmlPrologWriter != null )
        {
            detectEncoding( cbuf, off, len );
        }
        else
        {
            writer.write( cbuf, off, len );
        }
    }

    static final Pattern ENCODING_PATTERN = XmlReader.ENCODING_PATTERN;
}
