package com.ctc.wstx.io;

import java.io.*;

import com.ctc.wstx.api.ReaderConfig;

Simple Reader implementation that is used to "unwind" some data previously read from a Reader; 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 Reader. This is similar to PushbackReader, but with this class there's only one implicit pushback, when instance is constructed; not general pushback buffer and methods to use it. /**
 * Simple {@link Reader} implementation that is used to "unwind" some
 * data previously read from a Reader; 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 Reader.
 * This is similar to {@link java.io.PushbackReader}, but with this class
 * there's only one implicit pushback, when instance is constructed; not
 * general pushback buffer and methods to use it.
 */
public final class MergedReader
    extends Reader
{
    final ReaderConfig mConfig;

    final Reader mIn;

    
This buffer contains the partially read remains left over after
bootstrapper has consumed xml declaration (if one found).
It is generally recycled and can be returned after having been
read.
/**
     * This buffer contains the partially read remains left over after
     * bootstrapper has consumed xml declaration (if one found).
     * It is generally recycled and can be returned after having been
     * read.
     */
    char[] mData;

    int mPtr;

    final int mEnd;

    public MergedReader(ReaderConfig cfg, Reader in, char[] buf, int start, int end)
    {
        mConfig = cfg;
        mIn = in;
        mData = buf;
        mPtr = start;
        mEnd = end;
        // sanity check: should not pass empty buffer
        if (buf != null && start >= end) {
            throw new IllegalArgumentException("Trying to construct MergedReader with empty contents (start "+start+", end "+end+")");
        }
    }

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

    @Override
    public void mark(int readlimit) throws IOException
    {
        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(char[] cbuf) throws IOException {
        return read(cbuf, 0, cbuf.length);
    }

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

        return mIn.read(cbuf, off, len);
    }

    @Override
    public boolean ready() throws IOException
    {
        return (mData != null) || mIn.ready();
    }

    @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 amount;
            }
            freeMergedBuffer();
            count += amount;
            n -= amount;
        }

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

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