package com.jn.langx.codec;


import com.jn.langx.util.Preconditions;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import static com.jn.langx.codec.BaseNCodec.EOF;


/**
 * Abstract superclass for Base-N output streams.
 */
public class BaseNCodecOutputStream extends FilterOutputStream {

    private final boolean doEncode;

    private final BaseNCodec baseNCodec;

    private final byte[] singleByte = new byte[1];

    private final BaseNCodec.Context context = new BaseNCodec.Context();

    public BaseNCodecOutputStream(final OutputStream out, final BaseNCodec basedCodec, final boolean doEncode) {
        super(out);
        this.baseNCodec = basedCodec;
        this.doEncode = doEncode;
    }

    /**
     * Writes the specified <code>byte</code> to this output stream.
     *
     * @param i source byte
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void write(final int i) throws IOException {
        singleByte[0] = (byte) i;
        write(singleByte, 0, 1);
    }

    /**
     * Writes <code>len</code> bytes from the specified <code>b</code> array starting at <code>offset</code> to this
     * output stream.
     *
     * @param b      source byte array
     * @param offset where to start reading the bytes
     * @param len    maximum number of bytes to write
     * @throws IOException               if an I/O error occurs.
     * @throws NullPointerException      if the byte array parameter is null
     * @throws IndexOutOfBoundsException if offset, len or buffer size are invalid
     */
    @Override
    public void write(final byte b[], final int offset, final int len) throws IOException {
        Preconditions.checkNotNull(b);
        if (offset < 0 || len < 0) {
            throw new IndexOutOfBoundsException();
        } else if (offset > b.length || offset + len > b.length) {
            throw new IndexOutOfBoundsException();
        } else if (len > 0) {
            if (doEncode) {
                baseNCodec.encode(b, offset, len, context);
            } else {
                baseNCodec.decode(b, offset, len, context);
            }
            flush(false);
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream. If propagate is
     * true, the wrapped stream will also be flushed.
     *
     * @param propagate boolean flag to indicate whether the wrapped OutputStream should also be flushed.
     * @throws IOException if an I/O error occurs.
     */
    private void flush(final boolean propagate) throws IOException {
        final int avail = baseNCodec.available(context);
        if (avail > 0) {
            final byte[] buf = new byte[avail];
            final int c = baseNCodec.readResults(buf, 0, avail, context);
            if (c > 0) {
                out.write(buf, 0, c);
            }
        }
        if (propagate) {
            out.flush();
        }
    }

    /**
     * Flushes this output stream and forces any buffered output bytes to be written out to the stream.
     *
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void flush() throws IOException {
        flush(true);
    }

    /**
     * Closes this output stream and releases any system resources associated with the stream.
     * <p>
     * To write the EOF marker without closing the stream, call {@link #eof()} or use an
     * <a href="https://commons.apache.org/proper/commons-io/">Apache Commons IO</a> <a href=
     * "https://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/output/CloseShieldOutputStream.html"
     * >CloseShieldOutputStream</a>.
     * </p>
     *
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public void close() throws IOException {
        eof();
        flush();
        out.close();
    }

    /**
     * Writes EOF.
     *
     * @throws IOException if an I/O error occurs.
     */
    public void eof() throws IOException {
        // Notify encoder of EOF (-1).
        if (doEncode) {
            baseNCodec.encode(singleByte, 0, EOF, context);
        } else {
            baseNCodec.decode(singleByte, 0, EOF, context);
        }
    }

}
