/****************************************************************************
 * lib/stdio/lib_libfread.c
 *
 *   Copyright (C) 2007-2009, 2011 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 NuttX 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.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>  /* for CONFIG_STDIO_BUFFER_SIZE */

#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>

#include "lib_internal.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

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

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

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

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

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

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

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: lib_fread
 ****************************************************************************/

ssize_t lib_fread(FAR void *ptr, size_t count, FAR 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)
    {
      set_errno(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
      /* If the buffer is currently being used for write access, then
       * flush all of the buffered write data.  We do not support concurrent
       * buffered read/write access.
       */

      if (lib_wrflush(stream) != 0)
        {
          return ERROR;
        }

      /* 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
#if CONFIG_STDIO_BUFFER_SIZE > 0
    short_read:
#endif
      bytes_read = dest - (unsigned char*)ptr;
    err_out:
      lib_give_semaphore(stream);
    }
  return bytes_read;
}

