/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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.jboss.netty.util;

import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CodingErrorAction;
import java.util.IdentityHashMap;
import java.util.Map;

/**
 * A utility class that provides various common operations and constants
 * related with {@link Charset} and its relevant classes.
 */
public final class CharsetUtil {

    /**
     * 16-bit UTF (UCS Transformation Format) whose byte order is identified by
     * an optional byte-order mark
     */
    public static final Charset UTF_16 = Charset.forName("UTF-16");

    /**
     * 16-bit UTF (UCS Transformation Format) whose byte order is big-endian
     */
    public static final Charset UTF_16BE = Charset.forName("UTF-16BE");

    /**
     * 16-bit UTF (UCS Transformation Format) whose byte order is little-endian
     */
    public static final Charset UTF_16LE = Charset.forName("UTF-16LE");

    /**
     * 8-bit UTF (UCS Transformation Format)
     */
    public static final Charset UTF_8 = Charset.forName("UTF-8");

    /**
     * ISO Latin Alphabet No. 1, as known as <tt>ISO-LATIN-1</tt>
     */
    public static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");

    /**
     * 7-bit ASCII, as known as ISO646-US or the Basic Latin block of the
     * Unicode character set
     */
    public static final Charset US_ASCII = Charset.forName("US-ASCII");

    private static final ThreadLocal<Map<Charset, CharsetEncoder>> encoders =
        new ThreadLocal<Map<Charset, CharsetEncoder>>() {
            @Override
            protected Map<Charset, CharsetEncoder> initialValue() {
                return new IdentityHashMap<Charset, CharsetEncoder>();
            }
        };

    private static final ThreadLocal<Map<Charset, CharsetDecoder>> decoders =
        new ThreadLocal<Map<Charset, CharsetDecoder>>() {
            @Override
            protected Map<Charset, CharsetDecoder> initialValue() {
                return new IdentityHashMap<Charset, CharsetDecoder>();
            }
        };

    /**
     * Returns a cached thread-local {@link CharsetEncoder} for the specified
     * <tt>charset</tt>.
     */
    public static CharsetEncoder getEncoder(Charset charset) {
        if (charset == null) {
            throw new NullPointerException("charset");
        }

        Map<Charset, CharsetEncoder> map = encoders.get();
        CharsetEncoder e = map.get(charset);
        if (e != null) {
            e.reset();
            e.onMalformedInput(CodingErrorAction.REPLACE);
            e.onUnmappableCharacter(CodingErrorAction.REPLACE);
            return e;
        }

        e = charset.newEncoder();
        e.onMalformedInput(CodingErrorAction.REPLACE);
        e.onUnmappableCharacter(CodingErrorAction.REPLACE);
        map.put(charset, e);
        return e;
    }

    /**
     * Returns a cached thread-local {@link CharsetDecoder} for the specified
     * <tt>charset</tt>.
     */
    public static CharsetDecoder getDecoder(Charset charset) {
        if (charset == null) {
            throw new NullPointerException("charset");
        }

        Map<Charset, CharsetDecoder> map = decoders.get();
        CharsetDecoder d = map.get(charset);
        if (d != null) {
            d.reset();
            d.onMalformedInput(CodingErrorAction.REPLACE);
            d.onUnmappableCharacter(CodingErrorAction.REPLACE);
            return d;
        }

        d = charset.newDecoder();
        d.onMalformedInput(CodingErrorAction.REPLACE);
        d.onUnmappableCharacter(CodingErrorAction.REPLACE);
        map.put(charset, d);
        return d;
    }

    private CharsetUtil() {
        // Unused
    }
}
