package com.fasterxml.jackson.core.io;

import java.io.*;

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 IOContext _ctxt;

    final private InputStream _in;

    private byte[] _b;

    private int _ptr;

    final private int _end;

    public MergedStream(IOContext ctxt, InputStream in, byte[] buf, int start, int end) {
        _ctxt = ctxt;
        _in = in;
        _b = buf;
        _ptr = start;
        _end = end;
    }

    @Override
    public int available() throws IOException {
        if (_b != null) {
            return _end - _ptr;
        }
        return _in.available();
    }

    @Override public void close() throws IOException {
        _free();
        _in.close();
    }

    @Override public void mark(int readlimit) {
        if (_b == null) { _in.mark(readlimit); }
    }
    
    @Override public boolean markSupported() {
        // Only supports marks past the initial rewindable section...
        return (_b == null) && _in.markSupported();
    }
    
    @Override public int read() throws IOException {
        if (_b != null) {
            int c = _b[_ptr++] & 0xFF;
            if (_ptr >= _end) {
                _free();
            }
            return c;
        }
        return _in.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 (_b != null) {
            int avail = _end - _ptr;
            if (len > avail) {
                len = avail;
            }
            System.arraycopy(_b, _ptr, b, off, len);
            _ptr += len;
            if (_ptr >= _end) {
                _free();
            }
            return len;
        }
        return _in.read(b, off, len);
    }

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

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

        if (_b != null) {
            int amount = _end - _ptr;

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

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

    private void _free() {
        byte[] buf = _b;
        if (buf != null) {
            _b = null;
            if (_ctxt != null) {
                _ctxt.releaseReadIOBuffer(buf);
            }
        }
    }
}