/* GNU mailutils - a suite of utilities for electronic mail
   Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Library Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program 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 Library General Public License for more details.

   You should have received a copy of the GNU Library General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */

/* Notes:
First Draft: Dave Inglis.
 */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <filter0.h>

#define MU_TRANS_DECODE		1
#define MU_TRANS_ENCODE		2
#define MU_TRANS_BSIZE		2048

static int qp_init __P ((filter_t));
static int base64_init __P ((filter_t));

static struct _filter_record _qp_filter =
{
  "quoted-printable",
  qp_init,
  NULL,
  NULL,
  NULL
};

static struct _filter_record _base64_filter =
{
  "base64",
  base64_init,
  NULL,
  NULL,
  NULL
};

static struct _filter_record _bit8_filter =
{
  "8bit",
  NULL,
  NULL,
  NULL,
  NULL
};

static struct _filter_record _bit7_filter =
{
  "7bit",
  NULL,
  NULL,
  NULL,
  NULL
};

static struct _filter_record _binary_filter =
{
  "binary",
  NULL,
  NULL,
  NULL,
  NULL
};

/* Export.  */
filter_record_t qp_filter = &_qp_filter;
filter_record_t base64_filter = &_base64_filter;
filter_record_t binary_filter = &_binary_filter;
filter_record_t bit8_filter = &_bit8_filter;
filter_record_t bit7_filter = &_bit7_filter;

struct _trans_stream
{
  int t_offset; /* Orignal stream offset.  */

  size_t min_size;
  int s_offset;
  char *s_buf;     /* Used when read if not big enough to handle min_size
		      for decoder/encoder */

  int offset;      /* Current stream offset */
  int line_len;

  int w_rhd;       /* Working buffer read ahead  */
  int w_whd;       /* Working buffer write ahead */
  char w_buf[MU_TRANS_BSIZE]; /* working source/dest buffer */

  int (*transcoder) __P ((const char *iptr, size_t isize, char *optr,
			  size_t osize, size_t *nbytes, int *line_len));
};

static int base64_decode __P ((const char *iptr, size_t isize, char *optr,
				size_t osize, size_t *nbytes, int *line_len));
static int base64_encode __P ((const char *iptr, size_t isize, char *optr,
				size_t osize, size_t *nbytes, int *line_len));

static int qp_decode __P ((const char *iptr, size_t isize, char *optr,
			    size_t osize, size_t *nbytes, int *line_len));
static int qp_encode __P ((const char *iptr, size_t isize, char *optr,
			    size_t osize, size_t *nbytes, int *line_len));

static void
trans_destroy (filter_t filter)
{
  struct _trans_stream *ts = filter->data;
  if (ts->s_buf)
    free (ts->s_buf);
  free (ts);
}

static int
trans_read (filter_t filter, char *optr, size_t osize, off_t offset,
	     size_t *n_bytes)
{
  struct _trans_stream *ts = filter->data;
  size_t obytes, wbytes;
  int ret = 0, i;
  size_t bytes, *nbytes = &bytes;

  if (optr == NULL || osize == 0)
    return EINVAL;

  if (n_bytes)
    nbytes = n_bytes;
  *nbytes = 0;

  if (offset && ts->t_offset != offset)
    return ESPIPE;

  if (offset == 0)
    ts->s_offset = ts->t_offset = ts->w_whd = ts->w_rhd =
      ts->offset = ts->line_len = 0;

  while (*nbytes < osize)
    {
      if ((ts->w_rhd + (int)ts->min_size) >= ts->w_whd)
	{
	  memmove (ts->w_buf, ts->w_buf + ts->w_rhd, ts->w_whd - ts->w_rhd);
	  ts->w_whd = ts->w_whd - ts->w_rhd;
	  ts->w_rhd = 0;
	  ret = stream_read (filter->stream, ts->w_buf + ts->w_whd,
			     MU_TRANS_BSIZE - ts->w_whd, ts->offset,
			     &wbytes );
	  if (ret != 0)
	    break;
	  ts->offset += wbytes;
	  ts->w_whd += wbytes;
	}
      if ((osize - *nbytes) >= ts->min_size
	  && ts->s_offset == 0
	  && ts->w_whd - ts->w_rhd)
	{
	  ts->w_rhd += ts->transcoder (ts->w_buf + ts->w_rhd,
				       ts->w_whd - ts->w_rhd,
				       optr + *nbytes, osize - *nbytes,
				       &obytes, &ts->line_len);
	  if (ts->w_rhd > ts->w_whd) /* over shot due to padding */
	    ts->w_rhd = ts->w_whd;
	  *nbytes += obytes;
	  ts->t_offset += obytes;
	}
      else
	{
	  if (ts->s_offset == 0 && ts->w_whd - ts->w_rhd)
	    {
	      ts->w_rhd += ts->transcoder (ts->w_buf + ts->w_rhd,
					   ts->w_whd - ts->w_rhd, ts->s_buf,
					   ts->min_size, &obytes,
					   &ts->line_len);
	      if (ts->w_rhd > ts->w_whd) /* over shot due to padding */
		ts->w_rhd = ts->w_whd;
	      ts->s_offset = obytes;
	    }
	  for (i = ts->s_offset; i > 0; i--)
	    {
	      optr[(*nbytes)++] = ts->s_buf[ts->s_offset - i];
	      ts->t_offset++;
	      if (*nbytes >= osize)
		{
		  i--;
		  memmove (ts->s_buf, &ts->s_buf[ts->s_offset - i], i);
		  break;
		}
	    }
	  ts->s_offset = i;
	}
      if (wbytes == 0 && ts->s_offset == 0)
	break;
    }
  return ret;
}

#if 0
static int
trans_write (stream_t stream, const char *iptr, size_t isize, off_t offset,
	      size_t *nbytes)
{
  struct _trans_stream *ts = stream_get_owner (stream);
  return stream_write (ts->stream, iptr, isize, offset, nbytes);
}
#endif


/*------------------------------------------------------
 * base64 encode/decode
 *----------------------------------------------------*/

static int
b64_input (char c)
{
  const char table[64] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  int i;

  for (i = 0; i < 64; i++)
    {
      if (table[i] == c)
	return i;
    }
  return -1;
}

static int
base64_init (filter_t filter)
{
  struct _trans_stream *ts;
  ts = calloc (sizeof (*ts), 1);
  if (ts == NULL)
    return ENOMEM;

  ts->min_size = 4;
  ts->s_buf = calloc (4, 1);
  if (ts->s_buf == NULL)
    {
      free (ts);
      return ENOMEM;
    }
  ts->transcoder = (filter->type == MU_FILTER_DECODE) ? base64_decode : base64_encode;

  filter->_read = trans_read;
  filter->_destroy = trans_destroy;
  filter->data = ts;
  return 0;
}

static int
base64_decode (const char *iptr, size_t isize, char *optr, size_t osize,
	       size_t *nbytes, int *line_len)
{
  int i = 0, tmp = 0, pad = 0;
  size_t consumed = 0;
  char data[4];

  (void) line_len;
  *nbytes = 0;
  while (consumed < isize && (*nbytes)+3 < osize)
    {
      while (( i < 4 ) && (consumed < isize))
	{
	  tmp = b64_input (*iptr++);
	  consumed++;
	  if (tmp != -1)
	    data[i++] = tmp;
	  else if (*(iptr-1) == '=')
	    {
	      data[i++] = '\0';
	      pad++;
	    }
	}

      /* I have a entire block of data 32 bits get the output data.  */
      if (i == 4)
	{
	  *optr++ = (data[0] << 2) | ((data[1] & 0x30) >> 4);
	  *optr++ = ((data[1] & 0xf) << 4) | ((data[2] & 0x3c) >> 2);
	  *optr++ = ((data[2] & 0x3) << 6) | data[3];
	  (*nbytes) += 3 - pad;
	}
      else
	{
	  /* I did not get all the data.  */
	  consumed -= i;
	  return consumed;
	}
      i = 0;
    }
  return consumed;
}

#define BASE64_LINE_MAX 	77
static int
base64_encode (const char *iptr, size_t isize, char *optr, size_t osize,
	       size_t *nbytes, int *line_len)
{
  size_t consumed = 0;
  int pad = 0;
  const char *b64 =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  *nbytes = 0;
  if (isize <= 3)
    pad = 1;
  while (((consumed + 3) <= isize && (*nbytes + 4) <= osize) || pad)
    {
      if (*line_len == 76)
	{
	  *optr++ = '\n';
	  (*nbytes)++;
	  (*line_len) = 0;
	  if ((*nbytes + 4) > osize)
	    return consumed;
	}
      *optr++ = b64[iptr[0] >> 2];
      *optr++ = b64[((iptr[0] << 4) + (--isize ? (iptr[1] >> 4): 0)) & 0x3f];
      *optr++ = isize ?
	b64[((iptr[1] << 2) + (--isize ? (iptr[2] >> 6) : 0 )) & 0x3f]
	: '=';
      *optr++ = isize ? b64[iptr[2] & 0x3f] : '=';
      iptr += 3;
      consumed += 3;
      (*nbytes) += 4;
      (*line_len) +=4;
      pad = 0;
    }
  return consumed;
}

/*------------------------------------------------------
 * quoted-printable decoder/encoder
 *------------------------------------------------------*/
static const char _hexdigits[16] = "0123456789ABCDEF";

static int
qp_init (filter_t filter)
{
  struct _trans_stream *ts;
  ts = calloc (sizeof (*ts), 1);
  if (ts == NULL)
    return ENOMEM;

  ts->min_size = 4;
  ts->s_buf = calloc (4, 1);
  if (ts->s_buf == NULL)
    {
      free (ts);
      return ENOMEM;
    }
  ts->transcoder = (filter->type == MU_FILTER_DECODE) ? qp_decode : qp_encode;

  filter->_read = trans_read;
  filter->_destroy = trans_destroy;
  filter->data = ts;
  return 0;
}

static int
qp_decode (const char *iptr, size_t isize, char *optr, size_t osize,
	   size_t *nbytes, int *line_len)
{
  char c;
  int last_char = 0;
  size_t consumed = 0;

  (void)line_len;
  *nbytes = 0;
  while (consumed < isize && *nbytes < osize)
    {
      c = *iptr++;
      if (c == '=')
	{
	  /* There must be 2 more characters before I consume this.  */
	  if ((consumed + 2) >= isize)
	    return consumed;
	  else
	    {
	      /* you get =XX where XX are hex characters.  */
	      char 	chr[2];
	      int 	new_c;

	      chr[0] = *iptr++;
	      /* Ignore LF.  */
	      if (chr[0] != '\n')
		{
		  chr[1] = *iptr++;
		  new_c = strtoul (chr, NULL, 16);
		  *optr++ = new_c;
		  (*nbytes)++;
		  consumed += 3;
		}
	      else
		consumed += 2;
	    }
	}
      /* CR character.  */
      else if (c == '\r')
	{
	  /* There must be at least 1 more character before I consume this.  */
	  if ((consumed + 1) >= isize )
	    return (consumed);
	  else
	    {
	      iptr++; /* Skip the CR character.  */
	      *optr++ = '\n';
	      (*nbytes)++;
	      consumed += 2;
	    }
	}
      else if ((c == 9) || (c == 32))
	{
	  if ((last_char == 9) || (last_char == 32))
	    consumed++;
	  else
	    {
	      *optr++ = c;
	      (*nbytes)++;
	      consumed++;
	    }
	}
      else
	{
	  *optr++ = c;
	  (*nbytes)++;
	  consumed++;
	}
      last_char = c;
    }
  return consumed;
}

static int
qp_encode (const char *iptr, size_t isize, char *optr, size_t osize,
	   size_t *nbytes, int *line_len)
{
#define QP_LINE_MAX	76
  int c;
  size_t consumed = 0;

  (void)osize;
  *nbytes = 0;
  while (consumed < isize && (*nbytes + 4) < isize)
    {
      if (*line_len == QP_LINE_MAX)
	{
	  *optr++ = '=';
	  *optr++ = '\n';
	  (*nbytes) += 2;
	  *line_len = 0;
	}

      c = *iptr++;
      consumed++;
      if (((c >= 32) && (c <= 60)) || ((c >= 62) && (c <= 126)) || (c == 9))
	{
	  *optr++ = c;
	  (*nbytes)++;
	  (*line_len)++;
	}
      else
	{
	  if (*line_len >= (QP_LINE_MAX - 3))
	    {
	      /* add spaces.  */
	      while (*line_len < QP_LINE_MAX)
		{
		  *optr++ = ' ';
		  (*nbytes)++;
		  (*line_len)++;
		}
	      consumed--;
	      iptr--;
	    }
	  else
	    {
	      *optr++ = '=';
	      *optr++ = _hexdigits[c & 0xf];
	      *optr++ = _hexdigits[(c/16) & 0xf];
	      (*nbytes) += 3;
	      (*line_len) += 3;
	    }
	}
    }
  return consumed;
}