package com.jn.langx.codec;


import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

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


/**
 * Abstract superclass for Base-N input streams.
 */
public class BaseNCodecInputStream extends FilterInputStream {

    private final BaseNCodec baseNCodec;

    private final boolean doEncode;

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

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

    protected BaseNCodecInputStream(final InputStream in, final BaseNCodec baseNCodec, final boolean doEncode) {
        super(in);
        this.doEncode = doEncode;
        this.baseNCodec = baseNCodec;
    }

    /**
     * {@inheritDoc}
     *
     * @return <code>0</code> if the {@link InputStream} has reached <code>EOF</code>,
     * <code>1</code> otherwise
     */
    @Override
    public int available() throws IOException {
        // Note: the logic is similar to the InflaterInputStream:
        //       as long as we have not reached EOF, indicate that there is more
        //       data available. As we do not know for sure how much data is left,
        //       just return 1 as a safe guess.

        return context.eof ? 0 : 1;
    }

    /**
     * Marks the current position in this input stream.
     * <p>The {@link #mark} method of {@link BaseNCodecInputStream} does nothing.</p>
     *
     * @param readLimit the maximum limit of bytes that can be read before the mark position becomes invalid.
     * @see #markSupported()
     */
    @Override
    public synchronized void mark(final int readLimit) {
        // noop
    }

    /**
     * {@inheritDoc}
     *
     * @return Always returns <code>false</code>
     */
    @Override
    public boolean markSupported() {
        return false; // not an easy job to support marks
    }

    /**
     * Reads one <code>byte</code> from this input stream.
     *
     * @return the byte as an integer in the range 0 to 255. Returns -1 if EOF has been reached.
     * @throws IOException if an I/O error occurs.
     */
    @Override
    public int read() throws IOException {
        int r = read(singleByte, 0, 1);
        while (r == 0) {
            r = read(singleByte, 0, 1);
        }
        if (r > 0) {
            final byte b = singleByte[0];
            return b < 0 ? 256 + b : b;
        }
        return EOF;
    }

    /**
     * Attempts to read <code>len</code> bytes into the specified <code>b</code> array starting at <code>offset</code>
     * from this InputStream.
     *
     * @param b      destination byte array
     * @param offset where to start writing the bytes
     * @param len    maximum number of bytes to read
     * @return number of bytes read
     * @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 int read(final byte b[], final int offset, final int len) throws IOException {
        if (b == null) {
            throw new NullPointerException();
        } else if (offset < 0 || len < 0) {
            throw new IndexOutOfBoundsException();
        } else if (offset > b.length || offset + len > b.length) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        } else {
            int readLen = 0;
            /*
             Rationale for while-loop on (readLen == 0):
             -----
             Base32.readResults() usually returns > 0 or EOF (-1).  In the
             rare case where it returns 0, we just keep trying.

             This is essentially an undocumented contract for InputStream
             implementors that want their code to work properly with
             java.io.InputStreamReader, since the latter hates it when
             InputStream.read(byte[]) returns a zero.  Unfortunately our
             readResults() call must return 0 if a large amount of the data
             being decoded was non-base32, so this while-loop enables proper
             interop with InputStreamReader for that scenario.
             -----
             This is a fix for CODEC-101
            */
            while (readLen == 0) {
                if (!baseNCodec.hasData(context)) {
                    final byte[] buf = new byte[doEncode ? 4096 : 8192];
                    final int c = in.read(buf);
                    if (doEncode) {
                        baseNCodec.encode(buf, 0, c, context);
                    } else {
                        baseNCodec.decode(buf, 0, c, context);
                    }
                }
                readLen = baseNCodec.readResults(b, offset, len, context);
            }
            return readLen;
        }
    }

    /**
     * Repositions this stream to the position at the time the mark method was last called on this input stream.
     * <p>
     * The {@link #reset} method of {@link BaseNCodecInputStream} does nothing except throw an {@link IOException}.
     *
     * @throws IOException if this method is invoked
     */
    @Override
    public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
    }

    /**
     * {@inheritDoc}
     *
     * @throws IllegalArgumentException if the provided skip length is negative
     */
    @Override
    public long skip(final long n) throws IOException {
        if (n < 0) {
            throw new IllegalArgumentException("Negative skip length: " + n);
        }

        // skip in chunks of 512 bytes
        final byte[] b = new byte[512];
        long todo = n;

        while (todo > 0) {
            int len = (int) Math.min(b.length, todo);
            len = this.read(b, 0, len);
            if (len == EOF) {
                break;
            }
            todo -= len;
        }

        return n - todo;
    }
}
