/* This file is part of GNU tar.
   Copyright 2006-2023 Free Software Foundation, Inc.

   This program 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.

   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 General
   Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <system.h>
#include <regex.h>
#include "common.h"

enum transform_type
  {
    transform_first,
    transform_global
  };

enum replace_segm_type
  {
    segm_literal,   /* Literal segment */
    segm_backref,   /* Back-reference segment */
    segm_case_ctl   /* Case control segment (GNU extension) */
  };

enum case_ctl_type
  {
    ctl_stop,       /* Stop case conversion */
    ctl_upcase_next,/* Turn the next character to uppercase */
    ctl_locase_next,/* Turn the next character to lowercase */
    ctl_upcase,     /* Turn the replacement to uppercase until ctl_stop */
    ctl_locase      /* Turn the replacement to lowercase until ctl_stop */
  };

struct replace_segm
{
  struct replace_segm *next;
  enum replace_segm_type type;
  union
  {
    struct
    {
      char *ptr;
      size_t size;
    } literal;                /* type == segm_literal */
    size_t ref;               /* type == segm_backref */
    enum case_ctl_type ctl;   /* type == segm_case_ctl */
  } v;
};

struct transform
{
  struct transform *next;
  enum transform_type transform_type;
  int flags;
  unsigned match_number;
  regex_t regex;
  /* Compiled replacement expression */
  struct replace_segm *repl_head, *repl_tail;
  size_t segm_count; /* Number of elements in the above list */
};



static int transform_flags = XFORM_ALL;
static struct transform *transform_head, *transform_tail;

static struct transform *
new_transform (void)
{
  struct transform *p = xzalloc (sizeof *p);
  if (transform_tail)
    transform_tail->next = p;
  else
    transform_head = p;
  transform_tail = p;
  return p;
}

static struct replace_segm *
add_segment (struct transform *tf)
{
  struct replace_segm *segm = xmalloc (sizeof *segm);
  segm->next = NULL;
  if (tf->repl_tail)
    tf->repl_tail->next = segm;
  else
    tf->repl_head = segm;
  tf->repl_tail = segm;
  tf->segm_count++;
  return segm;
}

static void
add_literal_segment (struct transform *tf, const char *str, const char *end)
{
  size_t len = end - str;
  if (len)
    {
      struct replace_segm *segm = add_segment (tf);
      segm->type = segm_literal;
      segm->v.literal.ptr = xmalloc (len + 1);
      memcpy (segm->v.literal.ptr, str, len);
      segm->v.literal.ptr[len] = 0;
      segm->v.literal.size = len;
    }
}

static void
add_char_segment (struct transform *tf, int chr)
{
  struct replace_segm *segm = add_segment (tf);
  segm->type = segm_literal;
  segm->v.literal.ptr = xmalloc (2);
  segm->v.literal.ptr[0] = chr;
  segm->v.literal.ptr[1] = 0;
  segm->v.literal.size = 1;
}

static void
add_backref_segment (struct transform *tf, size_t ref)
{
  struct replace_segm *segm = add_segment (tf);
  segm->type = segm_backref;
  segm->v.ref = ref;
}

static int
parse_xform_flags (int *pflags, int c)
{
  switch (c)
    {
    case 'r':
      *pflags |= XFORM_REGFILE;
      break;

    case 'R':
      *pflags &= ~XFORM_REGFILE;
      break;

    case 'h':
      *pflags |= XFORM_LINK;
      break;

    case 'H':
      *pflags &= ~XFORM_LINK;
      break;

    case 's':
      *pflags |= XFORM_SYMLINK;
      break;

    case 'S':
      *pflags &= ~XFORM_SYMLINK;
      break;

    default:
      return 1;
    }
  return 0;
}

static void
add_case_ctl_segment (struct transform *tf, enum case_ctl_type ctl)
{
  struct replace_segm *segm = add_segment (tf);
  segm->type = segm_case_ctl;
  segm->v.ctl = ctl;
}

static const char *
parse_transform_expr (const char *expr)
{
  int delim;
  int i, j, rc;
  char *str, *beg, *cur;
  const char *p;
  int cflags = 0;
  struct transform *tf = new_transform ();

  if (expr[0] != 's')
    {
      if (strncmp (expr, "flags=", 6) == 0)
	{
	  transform_flags = 0;
	  for (expr += 6; *expr; expr++)
	    {
	      if (*expr == ';')
		{
		  expr++;
		  break;
		}
	      if (parse_xform_flags (&transform_flags, *expr))
		USAGE_ERROR ((0, 0, _("Unknown transform flag: %c"),
			      *expr));
	    }
	  return expr;
	}
      USAGE_ERROR ((0, 0, _("Invalid transform expression")));
    }

  delim = expr[1];
  if (!delim)
    USAGE_ERROR ((0, 0, _("Invalid transform expression")));

  /* Scan regular expression */
  for (i = 2; expr[i] && expr[i] != delim; i++)
    if (expr[i] == '\\' && expr[i+1])
      i++;

  if (expr[i] != delim)
    USAGE_ERROR ((0, 0, _("Invalid transform expression")));

  /* Scan replacement expression */
  for (j = i + 1; expr[j] && expr[j] != delim; j++)
    if (expr[j] == '\\' && expr[j+1])
      j++;

  if (expr[j] != delim)
    USAGE_ERROR ((0, 0, _("Invalid transform expression")));

  /* Check flags */
  tf->transform_type = transform_first;
  tf->flags = transform_flags;
  for (p = expr + j + 1; *p && *p != ';'; p++)
    switch (*p)
      {
      case 'g':
	tf->transform_type = transform_global;
	break;

      case 'i':
	cflags |= REG_ICASE;
	break;

      case 'x':
	cflags |= REG_EXTENDED;
	break;

      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
	tf->match_number = strtoul (p, (char**) &p, 0);
	p--;
	break;

      default:
	if (parse_xform_flags (&tf->flags, *p))
	  USAGE_ERROR ((0, 0, _("Unknown flag in transform expression: %c"),
			*p));
      }

  if (*p == ';')
    p++;

  /* Extract and compile regex */
  str = xmalloc (i - 1);
  memcpy (str, expr + 2, i - 2);
  str[i - 2] = 0;

  rc = regcomp (&tf->regex, str, cflags);

  if (rc)
    {
      char errbuf[512];
      regerror (rc, &tf->regex, errbuf, sizeof (errbuf));
      USAGE_ERROR ((0, 0, _("Invalid transform expression: %s"), errbuf));
    }

  if (str[0] == '^' || (i > 2 && str[i - 3] == '$'))
    tf->transform_type = transform_first;

  free (str);

  /* Extract and compile replacement expr */
  i++;
  str = xmalloc (j - i + 1);
  memcpy (str, expr + i, j - i);
  str[j - i] = 0;

  for (cur = beg = str; *cur;)
    {
      if (*cur == '\\')
	{
	  size_t n;

	  add_literal_segment (tf, beg, cur);
	  switch (*++cur)
	    {
	    case '0': case '1': case '2': case '3': case '4':
	    case '5': case '6': case '7': case '8': case '9':
	      n = strtoul (cur, &cur, 10);
	      if (n > tf->regex.re_nsub)
		USAGE_ERROR ((0, 0, _("Invalid transform replacement: back reference out of range")));
	      add_backref_segment (tf, n);
	      break;

	    case '\\':
	      add_char_segment (tf, '\\');
	      cur++;
	      break;

	    case 'a':
	      add_char_segment (tf, '\a');
	      cur++;
	      break;

	    case 'b':
	      add_char_segment (tf, '\b');
	      cur++;
	      break;

	    case 'f':
	      add_char_segment (tf, '\f');
	      cur++;
	      break;

	    case 'n':
	      add_char_segment (tf, '\n');
	      cur++;
	      break;

	    case 'r':
	      add_char_segment (tf, '\r');
	      cur++;
	      break;

	    case 't':
	      add_char_segment (tf, '\t');
	      cur++;
	      break;

	    case 'v':
	      add_char_segment (tf, '\v');
	      cur++;
	      break;

	    case '&':
	      add_char_segment (tf, '&');
	      cur++;
	      break;

	    case 'L':
	      /* Turn the replacement to lowercase until a '\U' or '\E'
		 is found, */
	      add_case_ctl_segment (tf, ctl_locase);
	      cur++;
	      break;

	    case 'l':
	      /* Turn the next character to lowercase, */
	      add_case_ctl_segment (tf, ctl_locase_next);
	      cur++;
	      break;

	    case 'U':
	      /* Turn the replacement to uppercase until a '\L' or '\E'
		 is found, */
	      add_case_ctl_segment (tf, ctl_upcase);
	      cur++;
	      break;

	    case 'u':
	      /* Turn the next character to uppercase, */
	      add_case_ctl_segment (tf, ctl_upcase_next);
	      cur++;
	      break;

	    case 'E':
	      /* Stop case conversion started by '\L' or '\U'. */
	      add_case_ctl_segment (tf, ctl_stop);
	      cur++;
	      break;

	    default:
	      if (*cur == delim)
		add_char_segment (tf, delim);
	      else
		{
		  char buf[2];
		  buf[0] = '\\';
		  buf[1] = *cur;
		  add_literal_segment (tf, buf, buf + 2);
		}
	      cur++;
	      break;
	    }
	  beg = cur;
	}
      else if (*cur == '&')
	{
	  add_literal_segment (tf, beg, cur);
	  add_backref_segment (tf, 0);
	  beg = ++cur;
	}
      else
	cur++;
    }
  add_literal_segment (tf, beg, cur);
  free(str);

  return p;
}

void
set_transform_expr (const char *expr)
{
  while (*expr)
    expr = parse_transform_expr (expr);
}

/* Run case conversion specified by CASE_CTL on array PTR of SIZE
   characters. Returns pointer to statically allocated storage. */
static char *
run_case_conv (enum case_ctl_type case_ctl, char *ptr, size_t size)
{
  static char *case_ctl_buffer;
  static size_t case_ctl_bufsize;
  char *p;

  if (case_ctl_bufsize < size)
    {
      case_ctl_bufsize = size;
      case_ctl_buffer = xrealloc (case_ctl_buffer, case_ctl_bufsize);
    }
  memcpy (case_ctl_buffer, ptr, size);
  switch (case_ctl)
    {
    case ctl_upcase_next:
      case_ctl_buffer[0] = toupper ((unsigned char) case_ctl_buffer[0]);
      break;

    case ctl_locase_next:
      case_ctl_buffer[0] = tolower ((unsigned char) case_ctl_buffer[0]);
      break;

    case ctl_upcase:
      for (p = case_ctl_buffer; p < case_ctl_buffer + size; p++)
	*p = toupper ((unsigned char) *p);
      break;

    case ctl_locase:
      for (p = case_ctl_buffer; p < case_ctl_buffer + size; p++)
	*p = tolower ((unsigned char) *p);
      break;

    case ctl_stop:
      break;
    }
  return case_ctl_buffer;
}


static struct obstack stk;
static bool stk_init;

static void
_single_transform_name_to_obstack (struct transform *tf, char *input)
{
  regmatch_t *rmp;
  int rc;
  size_t nmatches = 0;
  enum case_ctl_type case_ctl = ctl_stop,  /* Current case conversion op */
                     save_ctl = ctl_stop;  /* Saved case_ctl for \u and \l */

  /* Reset case conversion after a single-char operation */
#define CASE_CTL_RESET()  if (case_ctl == ctl_upcase_next     \
			      || case_ctl == ctl_locase_next) \
                            {                                 \
                              case_ctl = save_ctl;            \
                              save_ctl = ctl_stop;            \
			    }

  rmp = xmalloc ((tf->regex.re_nsub + 1) * sizeof (*rmp));

  while (*input)
    {
      size_t disp;
      char *ptr;

      rc = regexec (&tf->regex, input, tf->regex.re_nsub + 1, rmp, 0);

      if (rc == 0)
	{
	  struct replace_segm *segm;

	  disp = rmp[0].rm_eo;

	  nmatches++;
	  if (tf->match_number && nmatches < tf->match_number)
	    {
	      obstack_grow (&stk, input, disp);
	      input += disp;
	      continue;
	    }

	  if (rmp[0].rm_so)
	    obstack_grow (&stk, input, rmp[0].rm_so);

	  for (segm = tf->repl_head; segm; segm = segm->next)
	    {
	      switch (segm->type)
		{
		case segm_literal:    /* Literal segment */
		  if (case_ctl == ctl_stop)
		    ptr = segm->v.literal.ptr;
		  else
		    {
		      ptr = run_case_conv (case_ctl,
					   segm->v.literal.ptr,
					   segm->v.literal.size);
		      CASE_CTL_RESET();
		    }
		  obstack_grow (&stk, ptr, segm->v.literal.size);
		  break;

		case segm_backref:    /* Back-reference segment */
		  if (rmp[segm->v.ref].rm_so != -1
		      && rmp[segm->v.ref].rm_eo != -1)
		    {
		      size_t size = rmp[segm->v.ref].rm_eo
			              - rmp[segm->v.ref].rm_so;
		      ptr = input + rmp[segm->v.ref].rm_so;
		      if (case_ctl != ctl_stop)
			{
			  ptr = run_case_conv (case_ctl, ptr, size);
			  CASE_CTL_RESET();
			}

		      obstack_grow (&stk, ptr, size);
		    }
		  break;

		case segm_case_ctl:
		  switch (segm->v.ctl)
		    {
		    case ctl_upcase_next:
		    case ctl_locase_next:
		      switch (save_ctl)
			{
			case ctl_stop:
			case ctl_upcase:
			case ctl_locase:
			  save_ctl = case_ctl;
			default:
			  break;
			}
		      FALLTHROUGH;

		    case ctl_upcase:
		    case ctl_locase:
		    case ctl_stop:
		      case_ctl = segm->v.ctl;
		    }
		}
	    }
	}
      else
	{
	  disp = strlen (input);
	  obstack_grow (&stk, input, disp);
	}

      input += disp;

      if (tf->transform_type == transform_first)
	{
	  obstack_grow (&stk, input, strlen (input));
	  break;
	}
    }

  obstack_1grow (&stk, 0);
  free (rmp);
}

static bool
_transform_name_to_obstack (int flags, char *input, char **output)
{
  struct transform *tf;
  bool alloced = false;

  if (!stk_init)
    {
      obstack_init (&stk);
      stk_init = true;
    }

  for (tf = transform_head; tf; tf = tf->next)
    {
      if (tf->flags & flags)
	{
	  _single_transform_name_to_obstack (tf, input);
	  input = obstack_finish (&stk);
	  alloced = true;
	}
    }
  *output = input;
  return alloced;
}

bool
transform_name_fp (char **pinput, int flags,
		   char *(*fun)(char *, void *), void *dat)
{
    char *str;
    bool ret = _transform_name_to_obstack (flags, *pinput, &str);
    if (ret)
      {
	assign_string (pinput, fun ? fun (str, dat) : str);
	obstack_free (&stk, str);
      }
    else if (fun)
      {
	*pinput = NULL;
	assign_string (pinput, fun (str, dat));
	free (str);
	ret = true;
      }
    return ret;
}

bool
transform_name (char **pinput, int type)
{
  return transform_name_fp (pinput, type, NULL, NULL);
}

bool
transform_program_p (void)
{
  return transform_head != NULL;
}
