package com.alibaba.fastjson.serializer;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CodingErrorAction;

import com.alibaba.fastjson.JSONException;
import com.alibaba.fastjson.util.ThreadLocalCache;

public class SerialWriterStringEncoder {

    private final CharsetEncoder encoder;

    public SerialWriterStringEncoder(Charset cs) {
        this(cs.newEncoder().onMalformedInput(CodingErrorAction.REPLACE).onUnmappableCharacter(CodingErrorAction.REPLACE));
    }

    public SerialWriterStringEncoder(CharsetEncoder encoder) {
        this.encoder = encoder;
    }

    public byte[] encode(char[] chars, int off, int len) {
        if (len == 0) {
            return new byte[0];
        }

        encoder.reset();

        int bytesLength = scale(len, encoder.maxBytesPerChar());

        byte[] bytes = ThreadLocalCache.getBytes(bytesLength);

        return encode(chars, off, len, bytes);
    }

    public CharsetEncoder getEncoder() {
        return encoder;
    }

    public byte[] encode(char[] chars, int off, int len, byte[] bytes) {
        ByteBuffer byteBuf = ByteBuffer.wrap(bytes);

        CharBuffer charBuf = CharBuffer.wrap(chars, off, len);
        try {
            CoderResult cr = encoder.encode(charBuf, byteBuf, true);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
            cr = encoder.flush(byteBuf);
            if (!cr.isUnderflow()) {
                cr.throwException();
            }
        } catch (CharacterCodingException x) {
            // Substitution is always enabled,
            // so this shouldn't happen
            throw new JSONException(x.getMessage(), x);
        }

        int bytesLength = byteBuf.position();
        byte[] copy = new byte[bytesLength];
        System.arraycopy(bytes, 0, copy, 0, bytesLength);
        return copy;
    }

    private static int scale(int len, float expansionFactor) {
        // We need to perform double, not float, arithmetic; otherwise
        // we lose low order bits when len is larger than 2**24.
        return (int) (len * (double) expansionFactor);
    }
}