/* Simple inline comment filter for GNU Mailutils.
   Copyright (C) 2010-2012, 2014-2017 Free Software Foundation, Inc.

   GNU Mailutils 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 3, or (at your option)
   any later version.

   GNU Mailutils 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 Mailutils.  If not, see <http://www.gnu.org/licenses/>. */

/* In decode mode, this filter removes all inline comments from the input.
   An inline comment begins with a comment character sequence at the beginning
   of a line and ends with the next newline character.

   Default comment sequence is semicolon.  Another sequence can
   be given as the first argument to the filter creation routine.

   The following options modify this behavior:

      -i STR  Emit line number information after each contiguous sequence
              of removed lines.  STR supplies "information starter" -- a
	      sequence of characters which is output before the actual line
	      number.
      -r      Remove empty lines, i.e. the ones that contain only whitespace
              characters.
      -s      Squeeze whitespace.  Each sequence of two or more whitespace
              characters encountered on input is replaced by a single space
	      character on output.
      -S      A "following whitespace mode".  A comment sequence is
              recognized only if followed by a whitespace character.
	      The character itself is retained on output.  

   In encode mode, this filter adds a comment sequence at the beginning
   of each line.

   The following options apply to this mode:
   
      -S   A "following whitespace mode".  A single space character is
           output after each inserted comment sequence.
*/       

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <mailutils/errno.h>
#include <mailutils/filter.h>
#include <mailutils/cctype.h>
#include <mailutils/io.h>

enum ilcmt_state
  {
    ilcmt_initial,
    ilcmt_newline,
    ilcmt_copy,
    ilcmt_comment,
    ilcmt_partial,
    ilcmt_comment_ws,
    ilcmt_ws,
    ilcmt_rollback,
    ilcmt_rollback_ws
  };

#define ILCMT_REMOVE_EMPTY_LINES 0x001 /* Just that :) */
#define ILCMT_SQUEEZE_WS         0x002 /* Replace a series of whitespace
					  characters with a single space */
#define ILCMT_FOLLOW_WS          0x004 /* In decode mode: comment sequence is
					  recognized only if followed by a
					  whitespace character.
					  In encode mode: output a space after
					  each comment prefix. */
#define ILCMT_LINE_INFO          0x008 /* Emit line number information */ 

#define ILCMT_COMMENT_STATIC     0x0100
#define ILCMT_LINE_INFO_STATIC   0x0200
#define ILCMT_EMIT_LINE_INFO     0x0400

struct ilcmt_data
{
  enum ilcmt_state state;  /* Current state */
  char *comment;           /* Comment sequence ... */
  size_t length;           /* and its length */
  int flags;               /* ILCMT_ flags */
  char *line_info_starter;   /* Starter for line number info lines */
  unsigned long line_number; /* Current line number */
  char sbuf[3];            /* Static location for single-character strings */
  char *buf;               /* Rollback buffer ... */
  size_t size;             /* and its size */
  size_t level;            /* In ilcmt_partial state: number of bytes matched
			      in the comment sequence.
			      In other states: number of characters
			      stored in buf. */
  /* Rollback info: */
  char *rollback_buffer;   /* Actual rollback data */
  size_t rollback_size;    /* Size of rollback data */
  size_t rollback_index;   /* Index of the next-to-be-replayed character
			      in rollback_buffer */
};

#define ILCMT_BUF_INIT 80
#define ILCMT_BUF_INCR 16

static int
ilcmt_save (struct ilcmt_data *pd, int c)
{
  if (pd->level == pd->size)
    {
      size_t nsz;
      char *np;
      
      if (pd->size == 0)
	nsz = ILCMT_BUF_INIT;
      else
	nsz = pd->size + ILCMT_BUF_INCR;
      np = realloc (pd->buf, nsz);
      if (!np)
	return 1;
      pd->buf = np;
      pd->size = nsz;
    }
  pd->buf[pd->level++] = c;
  return 0;
}

static void
_ilcmt_free (struct ilcmt_data *pd)
{
  if (!(pd->flags & ILCMT_COMMENT_STATIC))
    free (pd->comment);
  if ((pd->flags & ILCMT_LINE_INFO) &&
      !(pd->flags & ILCMT_LINE_INFO_STATIC))
    free (pd->line_info_starter);
  free (pd->buf);
}

static void
init_rollback (struct ilcmt_data *pd, char *buf, size_t size)
{
  pd->state = ilcmt_rollback;
  pd->rollback_buffer = buf;
  pd->rollback_size = size;
  pd->rollback_index = 0;
}

static enum mu_filter_result
_ilcmt_decoder (void *xd, enum mu_filter_command cmd,
		struct mu_filter_io *iobuf)
{
  struct ilcmt_data *pd = xd;
  const unsigned char *iptr, *iend;
  char *optr, *oend;

  switch (cmd)
    {
    case mu_filter_init:
      pd->state = ilcmt_initial;
      return mu_filter_ok;
      
    case mu_filter_done:
      _ilcmt_free (pd);
      return mu_filter_ok;
      
    default:
      break;
    }
  
  iptr = (const unsigned char *) iobuf->input;
  iend = iptr + iobuf->isize;
  optr = iobuf->output;
  oend = optr + iobuf->osize;

  while (iptr < iend && optr < oend)
    {
      switch (pd->state)
	{
	case ilcmt_initial:
	case ilcmt_newline:
	  if (*iptr == *pd->comment)
	    {
	      iptr++;
	      pd->level = 1;
	      pd->state = ilcmt_partial;
	    }
	  else if (pd->flags & ILCMT_EMIT_LINE_INFO)
	    {
	      mu_asnprintf (&pd->buf, &pd->size, "%s %lu\n",
			    pd->line_info_starter,
			    pd->line_number);
	      init_rollback (pd, pd->buf, strlen (pd->buf));
	      pd->flags &= ~ILCMT_EMIT_LINE_INFO;
	    }
	  else if (*iptr == '\n')
	    {
	      pd->line_number++;
	      if (pd->flags & ILCMT_REMOVE_EMPTY_LINES)
		{
		  iptr++;
		  continue;
		}
	      else
		*optr++ = *iptr++;
	    }
	  else if (mu_isspace (*iptr))
	    {
	      if (pd->flags & ILCMT_REMOVE_EMPTY_LINES)
		{
		  pd->state = ilcmt_ws;
		  pd->level = 0;
		  if (!(pd->flags & ILCMT_SQUEEZE_WS))
		    {
		      if (ilcmt_save (pd, *iptr))
			return mu_filter_failure;
		    }
		  iptr++;
		}
	      else
		{
		  *optr++ = *iptr++;
		  pd->state = ilcmt_copy;
		}
	    }
	  else
	    {
	      *optr++ = *iptr++;
	      pd->state = ilcmt_copy;
	    }
	  break;
	  
	case ilcmt_partial:
	  if (pd->level == pd->length)
	    {
	      if (pd->flags & ILCMT_FOLLOW_WS)
		pd->state = ilcmt_comment_ws;
	      else
		pd->state = ilcmt_comment;
	    }
	  else if (*iptr == pd->comment[pd->level])
	    {
	      iptr++;
	      pd->level++;
	    }
	  else
	    {
	      /* Begin restoring */
	      init_rollback (pd, pd->comment, pd->level);
	    }
	  break;

	case ilcmt_comment_ws:
	  if (mu_isspace (*iptr))
	    {
	      if (*iptr != '\n')
		iptr++;
	      pd->state = ilcmt_comment;
	    }
	  else
	    {
	      /* Begin restoring */
	      if (pd->flags & ILCMT_EMIT_LINE_INFO)
		{
		  mu_asnprintf (&pd->buf, &pd->size, "%s %lu\n%.*s",
				pd->line_info_starter,
				pd->line_number,
				pd->level,
				pd->comment);
		  init_rollback (pd, pd->buf, strlen (pd->buf));
		  pd->flags &= ~ILCMT_EMIT_LINE_INFO;
		}
	      else
		init_rollback (pd, pd->comment, pd->level);
	    }
	  break;
	  
	case ilcmt_ws:
	  if (*iptr == '\n')
	    {
	      pd->line_number++;
	      iptr++;
	      pd->state = ilcmt_newline;
	    }
	  else if (mu_isspace (*iptr))
	    {
	      if (!(pd->flags & ILCMT_SQUEEZE_WS))
		{
		  if (ilcmt_save (pd, *iptr))
		    return mu_filter_failure;
		}
	      iptr++;
	    }
	  else
	    {
	      init_rollback (pd, pd->buf, pd->level);
	      pd->state = ilcmt_rollback_ws;
	    }
	  break;
      
	case ilcmt_copy:
	  if ((*optr++ = *iptr++) == '\n')
	    {
	      pd->line_number++;
	      pd->state = ilcmt_newline;
	    }
	  break;

	case ilcmt_comment:
	  if (*iptr++ == '\n')
	    {
	      pd->line_number++;
	      if (pd->flags & ILCMT_LINE_INFO)
		pd->flags |= ILCMT_EMIT_LINE_INFO;
	      pd->state = ilcmt_newline;
	    }
	  break;

	case ilcmt_rollback_ws:
	  if (pd->flags & ILCMT_SQUEEZE_WS)
	    {
	      *optr++ = ' ';
	      pd->state = ilcmt_copy;
	      break;
	    }
	  /* fall through */
	case ilcmt_rollback:
	  *optr++ = pd->rollback_buffer[pd->rollback_index++];
	  if (pd->rollback_index == pd->rollback_size)
	    pd->state = ilcmt_copy;
	}
    }
  iobuf->isize = iptr - (const unsigned char *) iobuf->input;
  iobuf->osize = optr - iobuf->output;
  return mu_filter_ok;
}

static enum mu_filter_result
_ilcmt_encoder (void *xd,
		enum mu_filter_command cmd,
		struct mu_filter_io *iobuf)
{
  struct ilcmt_data *pd = xd;
  const unsigned char *iptr, *iend;
  char *optr, *oend;

  switch (cmd)
    {
    case mu_filter_init:
      pd->state = ilcmt_initial;
      return mu_filter_ok;
      
    case mu_filter_done:
      _ilcmt_free (pd);
      return mu_filter_ok;
      
    default:
      break;
    }
  
  iptr = (const unsigned char *) iobuf->input;
  iend = iptr + iobuf->isize;
  optr = iobuf->output;
  oend = optr + iobuf->osize;

  while (iptr < iend && optr < oend)
    {
      switch (pd->state)
	{
	case ilcmt_initial:
	case ilcmt_newline:
	  init_rollback (pd, pd->comment, pd->length);
	case ilcmt_rollback:
	  *optr++ = pd->rollback_buffer[pd->rollback_index++];
	  if (pd->rollback_index == pd->rollback_size)
	    pd->state = (pd->flags & ILCMT_FOLLOW_WS) ?
	                   ilcmt_ws : ilcmt_copy;
	  break;

	case ilcmt_ws:
	  *optr++ = ' ';
	  pd->state = ilcmt_copy;
	case ilcmt_copy:
	  if ((*optr++ = *iptr++) == '\n')
	    pd->state = ilcmt_newline;
	  break;

	default:
	  /* The rest of states is not used, so: */
	  abort ();
	}
    }
  iobuf->isize = iptr - (const unsigned char *) iobuf->input;
  iobuf->osize = optr - iobuf->output;
  return mu_filter_ok;
}
      

static int
alloc_state (void **pret, int mode MU_ARG_UNUSED, int argc, const char **argv)
{
  struct ilcmt_data *pd = malloc (sizeof (*pd));
  int i;
  const char *comment = ";";
  const char *line_info;
  
  if (!pd)
    return ENOMEM;

  pd->flags = 0;
  pd->buf = NULL;
  pd->size = pd->level = 0;
  pd->line_number = 1;

  for (i = 1; i < argc; i++)
    {
      if (argv[i][0] == '-')
	{
	  switch (argv[i][1])
	    {
	    case 'r':
	      pd->flags |= ILCMT_REMOVE_EMPTY_LINES;
	      break;

	    case 's':
	      pd->flags |= ILCMT_SQUEEZE_WS;
	      break;

	    case 'S':
	      pd->flags |= ILCMT_FOLLOW_WS;
	      break;

	    case 'i':
	      pd->flags |= ILCMT_LINE_INFO;
	      if (i + 1 == argc)
		return MU_ERR_PARSE;
	      line_info = argv[++i];
	      break;
		
	    default:
	      free (pd);
	      return MU_ERR_PARSE;
	    }
	}
      else
	comment = argv[i];
    }
  if (comment[1] == 0)
    {
      pd->sbuf[0] = comment[0];
      pd->comment = pd->sbuf;
      pd->flags |= ILCMT_COMMENT_STATIC;
      pd->length = 1;
    }
  else
    {
      pd->comment = strdup (comment);
      if (!pd->comment)
	{
	  free (pd);
	  return ENOMEM;
	}
      pd->length = strlen (comment);
    }

  if (pd->flags & ILCMT_LINE_INFO)
    {
      if (line_info[1] == 0)
	{
	  pd->sbuf[1] = line_info[0];
	  pd->sbuf[2] = 0;
	  pd->line_info_starter = pd->sbuf + 1;
	  pd->flags |= ILCMT_LINE_INFO_STATIC;
	}
      else
	{
	  pd->line_info_starter = strdup (line_info);
	  if (!pd->line_info_starter)
	    {
	      if (!(pd->flags & ILCMT_COMMENT_STATIC))
		free (pd->comment);
	      free (pd);
	      return ENOMEM;
	    }
	}
    }
  
  *pret = pd;
  
  return 0;
}

static struct _mu_filter_record _inline_comment_filter = {
  "INLINE-COMMENT",
  alloc_state,
  _ilcmt_encoder,
  _ilcmt_decoder
};

mu_filter_record_t mu_inline_comment_filter = &_inline_comment_filter;