/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.stream.PushbackInputStream;


import hunt.stream.FilterInputStream;
import hunt.stream.Common;
import hunt.Exceptions;
import hunt.Integer;
import hunt.Long;
import hunt.math.Helper;

/**
*/
class PushbackInputStream : FilterInputStream {
    /**
     * The pushback buffer.
     */
    protected byte[] buf;

    /**
     * The position within the pushback buffer from which the next byte will
     * be read.  When the buffer is empty, <code>pos</code> is equal to
     * <code>buf.length</code>; when the buffer is full, <code>pos</code> is
     * equal to zero.
     *
     */
    protected int pos;

    /**
     * Check to make sure that this stream has not been closed
     */
    private void ensureOpen()  {
        if (inputStream is null)
            throw new IOException("Stream closed");
    }

    /**
     * Creates a <code>PushbackInputStream</code>
     * with a pushback buffer of the specified <code>size</code>,
     * and saves its argument, the input stream
     * <code>inputStream</code>, for later use. Initially,
     * the pushback buffer is empty.
     *
     * @param  inputStream    the input stream from which bytes will be read.
     * @param  size  the size of the pushback buffer.
     * @exception IllegalArgumentException if {@code size <= 0}
     */
    public this(InputStream inputStream, int size) {
        super(inputStream);
        if (size <= 0) {
            throw new IllegalArgumentException("size <= 0");
        }
        this.buf = new byte[size];
        this.pos = size;
    }

    /**
     * Creates a <code>PushbackInputStream</code>
     * with a 1-byte pushback buffer, and saves its argument, the input stream
     * <code>inputStream</code>, for later use. Initially,
     * the pushback buffer is empty.
     *
     * @param   inputStream   the input stream from which bytes will be read.
     */
    public this(InputStream inputStream) {
        this(inputStream, 1);
    }

    /**
     * Reads the next byte of data from this input stream. The value
     * byte is returned as an <code>int</code> inputStream the range
     * <code>0</code> to <code>255</code>. If no byte is available
     * because the end of the stream has been reached, the value
     * <code>-1</code> is returned. This method blocks until input data
     * is available, the end of the stream is detected, or an exception
     * is thrown.
     *
     * <p> This method returns the most recently pushed-back byte, if there is
     * one, and otherwise calls the <code>read</code> method of its underlying
     * input stream and returns whatever value that method returns.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             stream has been reached.
     * @exception  IOException  if this input stream has been closed by
     *             invoking its {@link #close()} method,
     *             or an I/O error occurs.
     * @see        java.io.InputStream#read()
     */
    override 
    public int read()  {
        ensureOpen();
        if (pos < buf.length) {
            return buf[pos++] & 0xff;
        }
        return super.read();
    }

    /**
     * Reads up to <code>len</code> bytes of data from this input stream into
     * an array of bytes.  This method first reads any pushed-back bytes; after
     * that, if fewer than <code>len</code> bytes have been read then it
     * reads from the underlying input stream. If <code>len</code> is not zero, the method
     * blocks until at least 1 byte of input is available; otherwise, no
     * bytes are read and <code>0</code> is returned.
     *
     * @param      b     the buffer into which the data is read.
     * @param      off   the start offset inputStream the destination array <code>b</code>
     * @param      len   the maximum number of bytes read.
     * @return     the total number of bytes read into the buffer, or
     *             <code>-1</code> if there is no more data because the end of
     *             the stream has been reached.
     * @exception  NullPointerException If <code>b</code> is <code>null</code>.
     * @exception  IndexOutOfBoundsException If <code>off</code> is negative,
     * <code>len</code> is negative, or <code>len</code> is greater than
     * <code>b.length - off</code>
     * @exception  IOException  if this input stream has been closed by
     *             invoking its {@link #close()} method,
     *             or an I/O error occurs.
     * @see        java.io.InputStream#read(byte[], int, int)
     */
    override
    public int read(byte[] b, int off, int len)  {
        ensureOpen();
        if (b is null) {
            throw new NullPointerException();
        } else if (off < 0 || len < 0 || len > b.length - off) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return 0;
        }

        int avail = cast(int)(buf.length - pos);
        if (avail > 0) {
            if (len < avail) {
                avail = len;
            }
            // System.arraycopy(buf, pos, b, off, avail);
            b[off..off+avail] = buf[pos..pos + avail];
            pos += avail;
            off += avail;
            len -= avail;
        }
        if (len > 0) {
            len = super.read(b, off, len);
            if (len == -1) {
                return avail == 0 ? -1 : avail;
            }
            return avail + len;
        }
        return avail;
    }

    /**
     * Pushes back a byte by copying it to the front of the pushback buffer.
     * After this method returns, the next byte to be read will have the value
     * <code>(byte)b</code>.
     *
     * @param      b   the <code>int</code> value whose low-order
     *                  byte is to be pushed back.
     * @exception IOException If there is not enough room inputStream the pushback
     *            buffer for the byte, or this input stream has been closed by
     *            invoking its {@link #close()} method.
     */
    public void unread(int b)  {
        ensureOpen();
        if (pos == 0) {
            throw new IOException("Push back buffer is full");
        }
        buf[--pos] = cast(byte)b;
    }

    /**
     * Pushes back a portion of an array of bytes by copying it to the front
     * of the pushback buffer.  After this method returns, the next byte to be
     * read will have the value <code>b[off]</code>, the byte after that will
     * have the value <code>b[off+1]</code>, and so forth.
     *
     * @param b the byte array to push back.
     * @param off the start offset of the data.
     * @param len the number of bytes to push back.
     * @exception IOException If there is not enough room inputStream the pushback
     *            buffer for the specified number of bytes,
     *            or this input stream has been closed by
     *            invoking its {@link #close()} method.
     */
    public void unread(byte[] b, int off, int len)  {
        ensureOpen();
        if (len > pos) {
            throw new IOException("Push back buffer is full");
        }
        pos -= len;
        // System.arraycopy(b, off, buf, pos, len);
        buf[pos .. pos + len] = b[off.. off+len];
    }

    /**
     * Pushes back an array of bytes by copying it to the front of the
     * pushback buffer.  After this method returns, the next byte to be read
     * will have the value <code>b[0]</code>, the byte after that will have the
     * value <code>b[1]</code>, and so forth.
     *
     * @param b the byte array to push back
     * @exception IOException If there is not enough room inputStream the pushback
     *            buffer for the specified number of bytes,
     *            or this input stream has been closed by
     *            invoking its {@link #close()} method.
     */
    public void unread(byte[] b)  {
        unread(b, 0, cast(int)(b.length));
    }

    /**
     * Returns an estimate of the number of bytes that can be read (or
     * skipped over) from this input stream without blocking by the next
     * invocation of a method for this input stream. The next invocation might be
     * the same thread or another thread.  A single read or skip of this
     * many bytes will not block, but may read or skip fewer bytes.
     *
     * <p> The method returns the sum of the number of bytes that have been
     * pushed back and the value returned by {@link
     * java.io.FilterInputStream#available available}.
     *
     * @return     the number of bytes that can be read (or skipped over) from
     *             the input stream without blocking.
     * @exception  IOException  if this input stream has been closed by
     *             invoking its {@link #close()} method,
     *             or an I/O error occurs.
     * @see        java.io.FilterInputStream#inputStream
     * @see        java.io.InputStream#available()
     */
    override
    public int available()  {
        ensureOpen();
        int n = cast(int)(buf.length - pos);
        int avail = super.available();
        return n > (Integer.MAX_VALUE - avail)
                    ? Integer.MAX_VALUE
                    : n + avail;
    }

    /**
     * Skips over and discards <code>n</code> bytes of data from this
     * input stream. The <code>skip</code> method may, for a variety of
     * reasons, end up skipping over some smaller number of bytes,
     * possibly zero.  If <code>n</code> is negative, no bytes are skipped.
     *
     * <p> The <code>skip</code> method of <code>PushbackInputStream</code>
     * first skips over the bytes inputStream the pushback buffer, if any.  It then
     * calls the <code>skip</code> method of the underlying input stream if
     * more bytes need to be skipped.  The actual number of bytes skipped
     * is returned.
     *
     * @param      n  {@inheritDoc}
     * @return     {@inheritDoc}
     * @throws     IOException  if the stream has been closed by
     *             invoking its {@link #close()} method,
     *             {@code inputStream.skip(n)} throws an IOException,
     *             or an I/O error occurs.
     * @see        java.io.FilterInputStream#inputStream
     * @see        java.io.InputStream#skip(long n)
     */
    override
    public long skip(long n)  {
        ensureOpen();
        if (n <= 0) {
            return 0;
        }

        long pskip = buf.length - pos;
        if (pskip > 0) {
            if (n < pskip) {
                pskip = n;
            }
            pos += pskip;
            n -= pskip;
        }
        if (n > 0) {
            pskip += super.skip(n);
        }
        return pskip;
    }

    /**
     * Tests if this input stream supports the <code>mark</code> and
     * <code>reset</code> methods, which it does not.
     *
     * @return   <code>false</code>, since this class does not support the
     *           <code>mark</code> and <code>reset</code> methods.
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.InputStream#reset()
     */
    override
    public bool markSupported() {
        return false;
    }

    /**
     * Marks the current position inputStream this input stream.
     *
     * <p> The <code>mark</code> method of <code>PushbackInputStream</code>
     * does nothing.
     *
     * @param   readlimit   the maximum limit of bytes that can be read before
     *                      the mark position becomes invalid.
     * @see     java.io.InputStream#reset()
     */
    public synchronized void mark(int readlimit) {
    }

    /**
     * Repositions this stream to the position at the time the
     * <code>mark</code> method was last called on this input stream.
     *
     * <p> The method <code>reset</code> for class
     * <code>PushbackInputStream</code> does nothing except throw an
     * <code>IOException</code>.
     *
     * @exception  IOException  if this method is invoked.
     * @see     java.io.InputStream#mark(int)
     * @see     java.io.IOException
     */
    public synchronized void reset()  {
        throw new IOException("mark/reset not supported");
    }

    /**
     * Closes this input stream and releases any system resources
     * associated with the stream.
     * Once the stream has been closed, further read(), unread(),
     * available(), reset(), or skip() invocations will throw an IOException.
     * Closing a previously closed stream has no effect.
     *
     * @exception  IOException  if an I/O error occurs.
     */
    override
    public  void close()  {
        synchronized{
            if (inputStream is null)
            return;
        inputStream.close();
        inputStream = null;
        buf = null;
        }
        
    }
}