/*
 *  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.tomcat.util.buf;

import java.io.CharArrayWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.BitSet;

/** Efficient implementation for encoders.
 *  This class is not thread safe - you need one encoder per thread.
 *  The encoder will save and recycle the internal objects, avoiding
 *  garbage.
 * 
 *  You can add extra characters that you want preserved, for example
 *  while encoding a URL you can add "/".
 *
 *  @author Costin Manolache
 *  @author Remy Maucherat
 */
public final class UEncoder {

    private static org.jboss.logging.Logger log =
        org.jboss.logging.Logger.getLogger(UEncoder.class);
    
    // Not static - the set may differ ( it's better than adding
    // an extra check for "/", "+", etc
    private BitSet safeChars=null;
    private C2BConverter c2b=null;
    private ByteChunk bb=null;
    private CharChunk cb=null;
    private CharChunk output=null;

    private String encoding="UTF8";
    private static final int debug=0;
    
    public UEncoder() {
        initSafeChars();
    }

    public void setEncoding( String s ) {
        encoding=s;
    }

    public void addSafeCharacter( char c ) {
        safeChars.set( c );
    }

    /** URL Encode string, using a specified encoding.
     *
     * @param buf The writer
     * @param s string to be encoded
     * @throws IOException If an I/O error occurs
     */
    public CharChunk encodeURL(String s, int start, int end)
        throws IOException {
        if (c2b == null) {
            bb = new ByteChunk(8); // small enough.
            cb = new CharChunk(2); // small enough.
            output = new CharChunk(64); // small enough.
            c2b = new C2BConverter(encoding);
        } else {
            bb.recycle();
            cb.recycle();
        }

        for (int i = start; i < end; i++) {
            char c = s.charAt(i);
            if (safeChars.get(c)) {
                if( debug > 0 ) log("Safe: " + (char)c);
                output.append(c);
            } else {
                if( debug > 0 ) log("Unsafe:  " + (char)c);
                cb.append(c);
                c2b.convert(cb, bb);

                // "surrogate" - UTF is _not_ 16 bit, but 21 !!!!
                // ( while UCS is 31 ). Amazing...
                if (c >= 0xD800 && c <= 0xDBFF) {
                    if ((i+1) < end) {
                        char d = s.charAt(i+1);
                        if (d >= 0xDC00 && d <= 0xDFFF) {
                            if( debug > 0 ) log("Unsafe:  " + d);
                            cb.append(d);
                            c2b.convert(cb, bb);
                            i++;
                        }
                    }
                }

                urlEncode(output, bb);
                cb.recycle();
                bb.recycle();
            }
        }
        
        return output;
    }

    protected void urlEncode(CharChunk out, ByteChunk bb)
        throws IOException {
        byte[] bytes = bb.getBuffer();
        for (int j = bb.getStart(); j < bb.getEnd(); j++) {
            out.append('%');
            char ch = Character.forDigit((bytes[j] >> 4) & 0xF, 16);
            out.append(ch);
            ch = Character.forDigit(bytes[j] & 0xF, 16);
            out.append(ch);
        }
    }
    
    // -------------------- Internal implementation --------------------
    
    // 
    private void init() {
	
    }
    
    private void initSafeChars() {
	safeChars=new BitSet(128);
	int i;
	for (i = 'a'; i <= 'z'; i++) {
	    safeChars.set(i);
	}
	for (i = 'A'; i <= 'Z'; i++) {
	    safeChars.set(i);
	}
	for (i = '0'; i <= '9'; i++) {
	    safeChars.set(i);
	}
	//safe
	safeChars.set('$');
	safeChars.set('-');
	safeChars.set('_');
	safeChars.set('.');

	// Dangerous: someone may treat this as " "
	// RFC1738 does allow it, it's not reserved
	//    safeChars.set('+');
	//extra
	safeChars.set('!');
	safeChars.set('*');
	safeChars.set('\'');
	safeChars.set('(');
	safeChars.set(')');
	safeChars.set(',');	
    }

    private static void log( String s ) {
        if (log.isDebugEnabled())
            log.debug("Encoder: " + s );
    }
}
