package com.ctc.wstx.io;

import java.io.*;

import com.ctc.wstx.api.ReaderConfig;

Simple InputStream implementation that is used to "unwind" some data previously read from an input stream; so that as long as some of that data remains, it's returned; but as long as it's read, we'll just use data from the underlying original stream. This is similar to PushbackInputStream, but here there's only one implicit pushback, when instance is constructed. /**
 * Simple {@link InputStream} implementation that is used to "unwind" some
 * data previously read from an input stream; so that as long as some of
 * that data remains, it's returned; but as long as it's read, we'll
 * just use data from the underlying original stream. 
 * This is similar to {@link java.io.PushbackInputStream}, but here there's
 * only one implicit pushback, when instance is constructed.
 */
public final class MergedStream
    extends InputStream
{
    final private ReaderConfig mConfig;

    final private  InputStream mIn;

    private byte[] mData;

    private int mPtr;

    final private int mEnd;

    public MergedStream(ReaderConfig cfg,
            InputStream in, byte[] buf, int start, int end)
    {
        if (in == null) {
            throw new IllegalArgumentException("InputStream `in` should not be `null`");
        }
        mConfig = cfg;
        mIn = in;
        mData = buf;
        mPtr = start;
        mEnd = end;
    }

    @Override
    public int available() throws IOException
    {
        if (mData != null) {
            return mEnd - mPtr;
        }
        return mIn.available();
    }

    @Override
    public void close() throws IOException
    {
        freeMergedBuffer();
        mIn.close();
    }

    @Override
    public void mark(int readlimit) {
        if (mData == null) {
            mIn.mark(readlimit);
        }
    }
    
    @Override
    public boolean markSupported() {
        // Only supports marks past the initial rewindable section...
        return (mData == null) && mIn.markSupported();
    }
    
    @Override
    public int read() throws IOException
    {
        if (mData != null) {
            int c = mData[mPtr++] & 0xFF;
            if (mPtr >= mEnd) {
                freeMergedBuffer();
            }
            return c;
        }
        return mIn.read();
    }
    
    @Override
    public int read(byte[] b) throws IOException
    {
        return read(b, 0, b.length);
    }

    @Override
    public int read(byte[] b, int off, int len) throws IOException
    {
        if (mData != null) {
            int avail = mEnd - mPtr;
            if (len > avail) {
                len = avail;
            }
            System.arraycopy(mData, mPtr, b, off, len);
            mPtr += len;
            if (mPtr >= mEnd) {
                freeMergedBuffer();
            }
            return len;
        }
        return mIn.read(b, off, len);
    }

    @Override
    public void reset() throws IOException
    {
        if (mData == null) {
            mIn.reset();
        }
    }

    @Override
    public long skip(long n) throws IOException
    {
        long count = 0L;

        if (mData != null) {
            int amount = mEnd - mPtr;

            if (amount > n) { // all in pushed back segment?
                mPtr += (int) n;
                return n;
            }
            freeMergedBuffer();
            count += amount;
            n -= amount;
        }

        if (n > 0) {
            count += mIn.skip(n);
        }
        return count;
    }

    private void freeMergedBuffer()
    {
        if (mData != null) {
            byte[] data = mData;
            mData = null;
            if (mConfig != null) {
                mConfig.freeFullBBuffer(data);
            }
        }
    }
}