/* This file is part of fileserv.
   Copyright (C) 2017-2023 Sergey Poznyakoff

   Fileserv 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.

   Fileserv 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 fileserv.  If not, see <http://www.gnu.org/licenses/>. */

#include <stdlib.h>
#include <errno.h>
#include "locus.h"

/* The line-tracker structure keeps track of the last N lines read from one
   or more input files.  For each line read it keeps the number of characters
   in that line including the newline.  This information is stored in a
   cyclic stack of N elements (N >= 2).  Top of stack always represents the
   current line.  For the purpose of line tracker, current line is the line
   that is being visited, such that its final newline character has not yet
   been seen.  Once the newline is seen, the line is pushed on stack, and a
   new current line is assumed.

   Each input file is represented by a directory entry keeping its name,
   the number of the first line that is stored in the tracker and the index of
   that line in the cols stack.  Entries form a doubly-linked list, with
   head pointing to the most recent (current) source.  When a new line is
   being added to the stack which is full, its eldest entry is discarded
   and re-assigned to that line; at the same time the directory of the
   eldest source is updated accordingly.  If the entry to be discarded
   represents the only line of the source, the source is discarded.   
*/

struct source
{
  char const *file_name; /* Name of the source file */
  size_t idx;            /* Index of the first element on stack */
  unsigned line;         /* Number of line corresponding to cols[idx] */
  struct source *next, *prev;
};

struct linetrack
{
  struct source *s_head, *s_tail;
                         /* Directory of source files.  Most recent one is
			    s_head */

  size_t max_lines;      /* Max. number of lines history kept by tracker (N) */
  size_t head;           /* Index of the eldest element on stack */
  size_t tos;            /* Index of the most recent element on stack
			    (< max_lines) */
  unsigned *cols;        /* Cyclic stack or character counts.
			    Number of characters in line (head + n) is
			    cols[head + n] (0 <= n <= tos). */
};

static inline size_t
trk_incr (struct linetrack *trk, size_t a)
{
  return (a + 1) % trk->max_lines;
}

static inline size_t
trk_decr (struct linetrack *trk, size_t a)
{
  return (a + trk->max_lines - 1) % trk->max_lines;
}
	 
static inline unsigned
count_lines (linetrack_t trk, size_t from)
{
  return (trk->tos + trk->max_lines - from) % trk->max_lines + 1;
}

#ifndef SIZE_MAX
# define SIZE_MAX (~((size_t)0))
#endif

static int
count_chars (struct linetrack *trk, size_t i, size_t *ret)
{
  size_t nch = 0;

  while (1)
    {
      unsigned n = trk->cols[i];
      if (SIZE_MAX - nch < n)
	return ERANGE;
      nch += n;
      if (i == trk->tos)
	break;
      i = trk_incr (trk, i);
    }
  *ret = nch;
  return 0;
}

static size_t
count_files (struct linetrack *trk)
{
  struct source *sp;
  size_t n = 0;
  for (sp = trk->s_head; sp; sp = sp->next)
    n++;
  return n;
}

static void
del_source (linetrack_t trk, struct source *sp)
{
  if (sp->prev)
    sp->prev->next = sp->next;
  else
    trk->s_head = sp->next;
  if (sp->next)
    sp->next->prev = sp->prev;
  else
    trk->s_tail = sp->prev;
  ident_deref (sp->file_name);
  free (sp);
}
  
static inline unsigned *
push (linetrack_t trk)
{
  trk->tos = trk_incr (trk, trk->tos);
  if (trk->tos == trk->head)
    {
      trk->head = trk_incr (trk, trk->head);
      trk->s_tail->idx = trk->head;
      trk->s_tail->line++;
    }
  if (trk->s_tail->prev && trk->s_tail->idx == trk->s_tail->prev->idx)
    del_source (trk, trk->s_tail);
  trk->cols[trk->tos] = 0;
  return &trk->cols[trk->tos];
}

static inline unsigned *
pop (linetrack_t trk)
{
  if (trk->tos == trk->head)
    return NULL;
  if (trk->tos == trk->s_head->idx)
    del_source (trk, trk->s_head);
  
  trk->tos = trk_decr (trk, trk->tos);
  
  return &trk->cols[trk->tos];
}

int
linetrack_origin (linetrack_t trk, struct locus_point const *pt)
{
  int rc;
  struct source *sp;
  char const *file_name;
  
  if (!trk || !pt || pt->line == 0)
    return EINVAL;
  if (pt->file)
    file_name = pt->file;
  else if (trk->s_head)
    file_name = trk->s_head->file_name;
  else
    return EINVAL;
  sp = malloc (sizeof *sp);
  if (!sp)
    return errno;
  rc = ident_ref (file_name, &sp->file_name);
  if (rc)
    {
      free (sp);
      return rc;
    }

  if (trk->cols[trk->tos])
    push (trk);
  
  sp->idx = trk->tos;
  sp->line = pt->line;
  trk->cols[sp->idx] = pt->col;

  sp->prev = NULL;
  sp->next = trk->s_head;
  if (trk->s_head)
    trk->s_head->prev = sp;
  else
    trk->s_tail = sp;
  trk->s_head = sp;
  return 0;
}

int
linetrack_create (linetrack_t *ret, char const *file_name, size_t max_lines)
{
  int rc;
  struct linetrack *trk;
  struct locus_point pt;
  
  trk = malloc (sizeof *trk);
  if (!trk)
    return errno;

  trk->cols = calloc (max_lines, sizeof (trk->cols[0]));
  if (!trk->cols)
    {
      rc = errno;
      free (trk);
      return rc;
    }
  trk->s_head = trk->s_tail = NULL;
  
  if (max_lines < 2)
    max_lines = 2;
  trk->max_lines = max_lines;
  trk->head = 0;
  trk->tos = 0;
  trk->cols[0] = 0;

  pt.file = file_name;
  pt.line = 1;
  pt.col = 0;
  rc = linetrack_origin (trk, &pt);
  if (rc)
    {
      free (trk->cols);
      free (trk);
      return rc;
    }
  
  *ret = trk;
  return 0;
}

int
linetrack_rebase (linetrack_t trk, struct locus_point const *pt)
{
  char const *file_name;
  int rc = ident_ref (pt->file, &file_name);
  if (rc)
    return rc;
  ident_deref (trk->s_head->file_name);
  trk->s_head->file_name = file_name;
  trk->s_head->line = pt->line;
  trk->cols[trk->s_head->idx] = pt->col;
  return 0;
}
  
void
linetrack_free (linetrack_t trk)
{
  if (trk)
    {
      while (trk->s_head)
	del_source (trk, trk->s_head);
      free (trk->cols);
      free (trk);
    }
}

void
linetrack_destroy (linetrack_t *trk)
{
  if (trk)
    {
      linetrack_free (*trk);
      *trk = NULL;
    }
}   

int
linetrack_stat (struct linetrack *trk, struct linetrack_stat *st)
{
  if (count_chars (trk, trk->head, &st->n_chars))
    return ERANGE;
  st->n_files = count_files (trk);
  st->n_lines = count_lines (trk, trk->head);
  return 0;
}

int
linetrack_at_bol (struct linetrack *trk)
{
  return trk->cols[trk->tos] == 0;
}

void
linetrack_advance (struct linetrack *trk,
		      struct locus_range *loc,
		      char const *text, size_t leng)
{
  unsigned *ptr;

  if (text == NULL || leng == 0)
    return;

  locus_point_set_file (&loc->beg, trk->s_head->file_name);
  locus_point_set_file (&loc->end, trk->s_head->file_name);
  loc->beg.line =
    trk->s_head->line + count_lines (trk, trk->s_head->idx) - 1;
  ptr = &trk->cols[trk->tos];
  loc->beg.col = *ptr + 1;
  while (leng--)
    {
      (*ptr)++;
      if (*text == '\n')
	ptr = push (trk);
      text++;
    }

  loc->end.line =
    trk->s_head->line + count_lines (trk, trk->s_head->idx) - 1;
  if (*ptr)
    {
      loc->end.col = *ptr;
    }
  else
    {
      /* Text ends with a newline.  Keep the previous line number. */
      loc->end.line--;
      loc->end.col = trk->cols[trk_decr (trk, trk->tos)] - 1;
      if (loc->end.col + 1 == loc->beg.col)
	{
	  /* This happens if the previous line contained only newline. */
	  loc->beg.col = loc->end.col;
	}	  
   }
}

int
linetrack_locus (struct linetrack *trk, struct locus_point *lp)
{
  int rc = locus_point_set_file (lp, trk->s_head->file_name);
  if (rc == 0)
    {
      lp->line =
	trk->s_head->line + count_lines (trk, trk->s_head->idx) - 1;
      lp->col = trk->cols[trk->tos];
    }
  return rc;
}

int
linetrack_retreat (struct linetrack *trk, size_t n)
{
  size_t nch;

  if (count_chars (trk, trk->head, &nch))
    return ERANGE;
  if (n > nch)
    return ERANGE;
  else
    {
      unsigned *ptr = &trk->cols[trk->tos];
      while (n--)
	{
	  if (*ptr == 0)
	    {
	      ptr = pop (trk);
	      if (!ptr || *ptr == 0)
		return ERANGE;
	    }
	  --*ptr;
	}
    }
  return 0;
}