/************************************************************
 * lib_libfread.c
 *
 *   Copyright (C) 2007 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name Gregory Nutt nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ************************************************************/

/************************************************************
 * Compilation Switches
 ************************************************************/

/************************************************************
 * Included Files
 ************************************************************/

#include <nuttx/config.h>  /* for CONFIG_STDIO_BUFFER_SIZE */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include "lib_internal.h"

/************************************************************
 * Definitions
 ************************************************************/

/************************************************************
 * Private Type Declarations
 ************************************************************/

/************************************************************
 * Private Function Prototypes
 ************************************************************/

/************************************************************
 * Global Constant Data
 ************************************************************/

/************************************************************
 * Global Variables
 ************************************************************/

/************************************************************
 * Private Constant Data
 ************************************************************/

/************************************************************
 * Private Variables
 ************************************************************/

/************************************************************
 * Global Functions
 ************************************************************/

/************************************************************
 * lib_fread
 ************************************************************/

#if CONFIG_NFILE_STREAMS > 0

ssize_t lib_fread(void *ptr, size_t count, FILE *stream)
{
  unsigned char *dest  = (unsigned char*)ptr;
  ssize_t        bytes_read;

  /* Make sure that reading from this stream is allowed */

  if ((!stream) || ((stream->fs_oflags & O_RDOK) == 0))
    {
      *get_errno_ptr() = EBADF;
      bytes_read = -1;
    }
  else
    {
      /* The stream must be stable until we complete the read */

      lib_take_semaphore(stream);

#if CONFIG_NUNGET_CHARS > 0
      /* First, re-read any previously ungotten characters */

      while ((stream->fs_nungotten > 0) && (count > 0))
	{
	  /* Decrement the count of ungotten bytes to get an index */

	  stream->fs_nungotten--;

	  /* Return the last ungotten byte */

	  *dest++ = stream->fs_ungotten[stream->fs_nungotten];

	  /* That's one less byte that we have to read */

	  count--;
	}
#endif

#if CONFIG_STDIO_BUFFER_SIZE > 0
      /* Now get any other needed chars from the buffer or the file. */

      while (count > 0)
	{
	  /* Is there readable data in the buffer? */

	  while ((count > 0) && (stream->fs_bufpos < stream->fs_bufread))
	    {
	      /* Yes, copy a byte into the user buffer */

	      *dest++ = *stream->fs_bufpos++;
	      count--;
	    }

	  /* The buffer is empty OR we have already supplied the number of
	   * bytes requested in the read.  Check if we need to read
	   * more from the file.
	   */

	  if (count > 0)
	    {
	      size_t buffer_available;

	      /* We need to read more data into the buffer from the file */

	      /* Mark the buffer empty */

	      stream->fs_bufpos = stream->fs_bufread = stream->fs_bufstart;

	      /* How much space is available in the buffer? */

	      buffer_available = stream->fs_bufend - stream->fs_bufread;

	      /* Will the number of bytes that we need to read fit into
	       * the buffer space that is available? If the read size is
	       * larger than the buffer, then read some of the data
	       * directly into the user's buffer.
	       */

	      if (count > buffer_available)
		{
		  bytes_read = read(stream->fs_filedes, dest, count);
		  if (bytes_read < 0)
		    {
		      /* An error occurred on the read */

		      goto err_out;
		    }
		  else if (bytes_read == 0)
		    {
		      /* We are at the end of the file */

		      goto short_read;
		    }
		  else
		    {
		      /* Some bytes were read. Adjust the dest pointer */

		      dest  += bytes_read;

		      /* Were all of the requested bytes read? */

		      if (bytes_read < count)
			{
			  /* No.  We must be at the end of file. */

			  goto short_read;
			}
		      else
			{
			  /* Yes.  We are done. */

			  count = 0;
			}
		    }
		}
	      else
		{
		  /* The number of bytes required to satisfy the read
		   * is less than or equal to the size of the buffer
		   * space that we have left. Read as much as we can
		   * into the buffer.
		   */

		  bytes_read = read(stream->fs_filedes, stream->fs_bufread, buffer_available);
		  if (bytes_read < 0)
		    {
		      /* An error occurred on the read */

		      goto err_out;
		    }
		  else if (bytes_read == 0)
		    {
		      /* We are at the end of the file */

		      goto short_read;
		    }
		  else
		    {
		      /* Some bytes were read */

		      stream->fs_bufread += bytes_read;
		    }
		}
	    }
	}
#else
      /* Now get any other needed chars from the file. */

      while (count > 0)
	{
	  bytes_read = read(stream->fs_filedes, dest, count);
	  if (bytes_read < 0)
	    {
	      goto err_out;
	    }
	  else if (bytes_read == 0)
	    {
	      break;
	    }
	  else
	    {
	      dest  += bytes_read;
	      count -= bytes_read;
	    }
	}
#endif
    short_read:
      bytes_read = dest - (unsigned char*)ptr;
    err_out:
      lib_give_semaphore(stream);
    }
  return bytes_read;
}

#endif /* CONFIG_NFILE_STREAMS */