/* -*- c++ -*- */
/*
 * Copyright 2004 Free Software Foundation, Inc.
 * 
 * This file is part of GNU Radio
 * 
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 * 
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <gr_buffer.h>
#include <gr_vmcircbuf.h>
#include <gr_math.h>
#include <stdexcept>
#include <iostream>
#include <assert.h>
#include <algorithm>

static long s_buffer_count = 0;		// counts for debugging storage mgmt
static long s_buffer_reader_count = 0;

// ----------------------------------------------------------------------------
//			Notes on storage management
//
// Pretty much all the fundamental classes are now using the
// shared_ptr stuff for automatic reference counting.  To ensure that
// no mistakes are made, we make the constructors for classes private,
// and then provide a free factory function that returns a smart
// pointer to the desired class.
//
// gr_buffer and gr_buffer_reader are no exceptions.  However, they
// both want pointers to each other, and unless we do something, we'll
// never delete any of them because of the circular structure.
// They'll always have a reference count of at least one.  We could
// use boost::weak_ptr's from gr_buffer to gr_buffer_reader but that
// introduces it's own problems.  (gr_buffer_reader's destructor needs
// to call gr_buffer::drop_reader, but has no easy way to get a
// shared_ptr to itself.)
//
// Instead, we solve this problem by having gr_buffer hold a raw
// pointer to gr_buffer_reader in its d_reader vector.
// gr_buffer_reader's destructor calls gr_buffer::drop_reader, so
// we're never left with an dangling pointer.  gr_buffer_reader still
// has a shared_ptr to the buffer ensuring that the buffer doesn't go
// away under it.  However, when the reference count of a
// gr_buffer_reader goes to zero, we can successfully reclaim it.
// ----------------------------------------------------------------------------


/*
 * Compute the minimum number of buffer items that work (i.e.,
 * address space wrap-around works).  To work is to satisfy this
 * contraint for integer buffer_size and k:
 *
 *     type_size * nitems == k * page_size
 */
static long
minimum_buffer_items (long type_size, long page_size)
{
  return page_size / gr_gcd (type_size, page_size);
}


gr_buffer::gr_buffer (int nitems, size_t sizeof_item)
  : d_base (0), d_bufsize (0), d_vmcircbuf (0),
    d_sizeof_item (sizeof_item), d_write_index (0),
    d_done (false)
{
  if (!allocate_buffer (nitems, sizeof_item))
    throw std::bad_alloc ();

  s_buffer_count++;
}

gr_buffer_sptr 
gr_make_buffer (int nitems, size_t sizeof_item)
{
  return gr_buffer_sptr (new gr_buffer (nitems, sizeof_item));
}

gr_buffer::~gr_buffer ()
{
  delete d_vmcircbuf;
  assert (d_readers.size() == 0);
  s_buffer_count--;
}

/*!
 * sets d_vmcircbuf, d_base, d_bufsize.
 * returns true iff successful.
 */
bool
gr_buffer::allocate_buffer (int nitems, size_t sizeof_item)
{
  int	orig_nitems = nitems;
  
  // Any buffersize we come up with must be a multiple of min_nitems.

  int granularity = gr_vmcircbuf_sysconfig::granularity ();
  int min_nitems =  minimum_buffer_items (sizeof_item, granularity);

  // Round-up nitems to a multiple of min_nitems.

  if (nitems % min_nitems != 0)
    nitems = ((nitems / min_nitems) + 1) * min_nitems;

  // If we rounded-up a whole bunch, give the user a heads up.
  // This only happens if sizeof_item is not a power of two.

  if (nitems > 2 * orig_nitems && nitems * (int) sizeof_item > granularity){
    std::cerr << "gr_buffer::allocate_buffer: warning: tried to allocate\n"
	      << "   " << orig_nitems << " items of size "
	      << sizeof_item << ". Due to alignment requirements\n"
	      << "   " << nitems << " were allocated.  If this isn't OK, consider padding\n"
	      << "   your structure to a power-of-two bytes.\n"
	      << "   On this platform, our allocation granularity is " << granularity << " bytes.\n";
  }

  d_bufsize = nitems;
  d_vmcircbuf = gr_vmcircbuf_sysconfig::make (d_bufsize * d_sizeof_item);
  if (d_vmcircbuf == 0){
    std::cerr << "gr_buffer::allocate_buffer: failed to allocate buffer of size "
	      << d_bufsize * d_sizeof_item / 1024 << " KB\n";
    return false;
  }

  d_base = (char *) d_vmcircbuf->pointer_to_first_copy ();
  return true;
}


int
gr_buffer::space_available () const
{
  if (d_readers.empty ())
    return d_bufsize - 1;	// See comment below

  else {

    // Find out the maximum amount of data available to our readers

    int	most_data = d_readers[0]->items_available ();
    for (unsigned int i = 1; i < d_readers.size (); i++)
      most_data = std::max (most_data, d_readers[i]->items_available ());

    // The -1 ensures that the case d_write_index == d_read_index is
    // unambiguous.  It indicates that there is no data for the reader

    return d_bufsize - most_data - 1;
  }
}

void *
gr_buffer::write_pointer ()
{
  return &d_base[d_write_index * d_sizeof_item];
}

void
gr_buffer::update_write_pointer (int nitems)
{
  d_write_index = index_add (d_write_index, nitems);
}

gr_buffer_reader_sptr
gr_buffer_add_reader (gr_buffer_sptr buf, int history)
{
  gr_buffer_reader_sptr r (new gr_buffer_reader (buf,
						 buf->index_sub(buf->d_write_index,
								history-1)));
  buf->d_readers.push_back (r.get ());

  return r;
}

void
gr_buffer::drop_reader (gr_buffer_reader *reader)
{
  // isn't C++ beautiful...    GAG!

  std::vector<gr_buffer_reader *>::iterator result =
    std::find (d_readers.begin (), d_readers.end (), reader);

  if (result == d_readers.end ())
    throw std::invalid_argument ("gr_buffer::drop_reader");    // we didn't find it...

  d_readers.erase (result);
}

long
gr_buffer_ncurrently_allocated ()
{
  return s_buffer_count;
}

// ----------------------------------------------------------------------------

gr_buffer_reader::gr_buffer_reader (gr_buffer_sptr buffer, unsigned int read_index)
  : d_buffer (buffer), d_read_index (read_index)
{
  s_buffer_reader_count++;
}

gr_buffer_reader::~gr_buffer_reader ()
{
  d_buffer->drop_reader(this);
  s_buffer_reader_count--;
}
   
int
gr_buffer_reader::items_available () const
{
  return d_buffer->index_sub (d_buffer->d_write_index, d_read_index);
}

const void *
gr_buffer_reader::read_pointer ()
{
  return &d_buffer->d_base[d_read_index * d_buffer->d_sizeof_item];
}

void
gr_buffer_reader::update_read_pointer (int nitems)
{
  d_read_index = d_buffer->index_add (d_read_index, nitems);
}

long
gr_buffer_reader_ncurrently_allocated ()
{
  return s_buffer_reader_count;
}