/****************************************************************************
 * libs/libc/stdio/lib_libdgets.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>

#include <stdbool.h>
#include <stdio.h>
#include <unistd.h>

#include "libc.h"

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

/****************************************************************************
 * Private Functions
 ****************************************************************************/

static int dgetc(int fd)
{
  unsigned char c;
  return read(fd, &c, 1) == 1 ? c : EOF;
}

/****************************************************************************
 * Name: consume_eol
 *
 * Description:
 *   If 'consume' is true, then consume_eol() will read and discard bytes
 *   from 'fd' until an EOF or a newline encountered or until a read
 *   error occurs.
 *
 ****************************************************************************/

static void consume_eol(int fd, bool consume)
{
  if (consume)
    {
      int ch;

      do
        {
          ch = dgetc(fd);
        }
      while (ch != EOF && ch != '\n');
    }
}

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

/****************************************************************************
 * Name: lib_dgets
 *
 * Description:
 *   lib_dgets() implements the core logic for both gets() and gets_s().
 *   lib_dgets() reads in at most one less than 'buflen' characters from
 *   fd and stores them into the buffer pointed to by 'buf'. Reading
 *   stops after an EOF or a newline encountered or after a read error
 *   occurs.
 *
 *   If a newline is read, it is stored into the buffer only if 'keepnl' is
 *   set true.  A null terminator is always stored after the last character
 *   in the buffer.
 *
 *   If 'buflen'-1 bytes were read into 'buf' without encountering an EOF
 *   or newline then the following behavior depends on the value of
 *   'consume':  If consume is true, then lib_dgets() will continue reading
 *   bytes and discarding them until an EOF or a newline encountered or
 *   until a read error occurs.  Otherwise, lib_dgets() returns with the
 *   remaining of the incoming stream buffer.
 *
 ****************************************************************************/

FAR char *lib_dgets(FAR char *buf, size_t buflen, int fd,
                    bool keepnl, bool consume)
{
  size_t nch = 0;

  /* Sanity checks */

  if (!buf || fd < 0)
    {
      return NULL;
    }

  /* Make sure that we have a buffer and space for at least one character */

  if (buflen < 1)
    {
      consume_eol(fd, consume);
      return NULL;
    }

  /* Make sure that we have space for something in addition to the NUL
   * terminator.
   */

  if (buflen < 2)
    {
      *buf = '\0';
      consume_eol(fd, consume);
      return buf;
    }

  /* Read characters until we have a full line. On each the loop we must
   * be assured that there are two free bytes in the line buffer:  One for
   * the next character and one for the null terminator.
   */

  for (; ; )
    {
      /* Get the next character */

      int ch = dgetc(fd);

      /* Check for end-of-line.  This is tricky only in that some
       * environments may return CR as end-of-line, others LF, and
       * others both.
       */

      if (ch == '\n')
        {
          /* Convert \r\n to \n */

          if (nch > 0 && buf[nch - 1] == '\r')
            {
              --nch;
            }

          if (keepnl)
            {
              /* Store newline is stored in the buffer */

              buf[nch++] = '\n';
            }

          /* Terminate the string */

          buf[nch] = '\0';
          return buf;
        }

      /* Check for end-of-file */

      else if (ch == EOF)
        {
          /* End of file with no data? */

          if (nch == 0)
            {
              /* Yes.. return NULL as the end of file mark */

              return NULL;
            }
          else
            {
              /* No, terminate the accumulated string */

              buf[nch] = '\0';
              return buf;
            }
        }

      /* Otherwise, put the character in the line buffer */

      else
        {
          buf[nch++] = ch;

          /* Check if there is room for another character and the line's
           * NUL terminator.  If not then we have to end the line now,
           * perhaps consuming any data up to the end-of-line.
           */

          if (nch + 1 >= buflen)
            {
              buf[nch] = '\0';
              consume_eol(fd, consume);
              return buf;
            }
        }
    }
}