/* This file implements an efficient interval data-structure.

Copyright (C) 2017-2022  Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs 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 of the License, or (at
your option) any later version.

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

#ifndef ITREE_H
#define ITREE_H
#include <config.h>
#include <stddef.h>
#include <inttypes.h>

#include "lisp.h"

/* The tree and node structs are mainly here, so they can be
   allocated.

   NOTE: The only time where it is safe to modify node.begin and
   node.end directly, is while the node is not part of any tree.

   NOTE: It is safe to read node.begin and node.end directly, if the
   node came from a generator, because it validates the nodes it
   returns as a side-effect.
 */

struct interval_node;
struct interval_node
{
  /* The normal parent, left and right links found in binary trees.
     See also `red`, below, which completes the Red-Black tree
     representation.  */
  struct interval_node *parent;
  struct interval_node *left;
  struct interval_node *right;

  /* The following five fields comprise the interval abstraction.

     BEGIN, END are buffer positions describing the range.  When a
     node is in a tree these fields are read only, written only by
     itree functions.

     The LIMIT, OFFSET and OTICK fields should be considered internal
     to itree.c and used only by itree functions.

     LIMIT is a buffer position, the maximum of END of this node and
     its children.  See itree.c for its use.

     OFFSET is in buffer position units, and will be non-zero only
     when the node is dirty.

     OTICK determines whether BEGIN, END, LIMIT and OFFSET are
     considered dirty.  A node is clean when its OTICK is equal to the
     OTICK of its tree (see struct interval_tree).  Otherwise, it is
     dirty.

     In a clean node, BEGIN, END and LIMIT are correct buffer
     positions, and OFFSET is zero.  The parent of a clean node is
     also clean, recursively.

     In a dirty node, the node's OTICK won't equal its tree's OTICK,
     and its OFFSET may be non-zero.  At all times the descendents of
     a dirty node are also dirty.  BEGIN, END and LIMIT require
     adjustment before use as buffer positions.

     NOTE: BEGIN and END must not be modified while the node is part
     of a tree.  Use interval_tree_insert_gap and
     interval_tree_delete_gap instead.

     NOTE: The interval generators ensure nodes are clean before
     yielding them, so BEGIN and END may be safely used as buffer
     positions then.
  */

  ptrdiff_t begin;		/* The beginning of this interval. */
  ptrdiff_t end;		/* The end of the interval. */
  ptrdiff_t limit;		/* The maximum end in this subtree. */
  ptrdiff_t offset;		/* The amount of shift to apply to this subtree. */
  uintmax_t otick;              /* offset modified tick */
  Lisp_Object data;             /* Exclusively used by the client. */
  bool_bf red : 1;
  bool_bf rear_advance : 1;     /* Same as for marker and overlays.  */
  bool_bf front_advance : 1;    /* Same as for marker and overlays.  */
};

/* The sentinel node, the null node.  */
extern struct interval_node itree_null;
#define ITREE_NULL (&itree_null)

struct interval_tree
{
  struct interval_node *root;
  uintmax_t otick;              /* offset tick, compared with node's otick. */
  intmax_t size;                /* Number of nodes in the tree. */
};

enum interval_tree_order {
  ITREE_ASCENDING,
  ITREE_DESCENDING,
  ITREE_PRE_ORDER,
};

void interval_node_init (struct interval_node *, bool, bool, Lisp_Object);
ptrdiff_t interval_node_begin (struct interval_tree *, struct interval_node *);
ptrdiff_t interval_node_end (struct interval_tree *, struct interval_node *);
void interval_node_set_region (struct interval_tree *, struct interval_node *, ptrdiff_t, ptrdiff_t);
struct interval_tree *interval_tree_create (void);
void interval_tree_destroy (struct interval_tree *);
intmax_t interval_tree_size (struct interval_tree *);
void interval_tree_clear (struct interval_tree *);
void itree_insert_node (struct interval_tree *tree, struct interval_node *node,
                        ptrdiff_t begin, ptrdiff_t end);
struct interval_node *interval_tree_remove (struct interval_tree *, struct interval_node *);
struct interval_generator *interval_tree_iter_start (struct interval_tree *, ptrdiff_t, ptrdiff_t, enum interval_tree_order,
			       const char* file, int line);
void interval_generator_narrow (struct interval_generator *, ptrdiff_t, ptrdiff_t);
void interval_tree_iter_finish (struct interval_generator *);
struct interval_node *interval_generator_next (struct interval_generator *);
void interval_tree_insert_gap (struct interval_tree *, ptrdiff_t, ptrdiff_t);
void interval_tree_delete_gap (struct interval_tree *, ptrdiff_t, ptrdiff_t);
bool itree_busy_p (void);

/* Iterate over the intervals between BEG and END in the tree T.
   N will hold successive nodes.  ORDER can be one of : `ASCENDING`,
   `DESCENDING`, or `PRE_ORDER`.
   It should be used as:

      ITREE_FOREACH (n, t, beg, end, order)
        {
          .. do the thing with n ..
        }

   BEWARE:
   - The expression T may be evaluated more than once, so make sure
     it is cheap a pure.
   - Only a single iteration can happen at a time, so make sure none of the
     code within the loop can start another tree iteration, i.e. it shouldn't
     be able to run ELisp code (or GC for that matter).
   - If you need to exit the loop early, you *have* to call `ITREE_ABORT`
     just before exiting (e.g. with `break` or `return`).
   - Non-local exits are not supported within the body of the loop.
   - Don't modify the tree during the iteration.
 */
#define ITREE_FOREACH(n, t, beg, end, order)                        \
  /* FIXME: We'd want to declare `x` right here, but I can't figure out
     how to make that work here: the `for` syntax only allows a single
     clause for the var declarations where we need 2 different types.
     We could use the `struct {foo x; bar y; } p;` trick to declare two
     vars `p.x` and `p.y` of unrelated types, but then none of the names
     of the vars matches the `n` we receive :-(.  */                \
  if (!t)                                                           \
    { }                                                             \
  else                                                              \
    for (struct interval_generator *itree_iter_                     \
            = interval_tree_iter_start (t, beg, end, ITREE_##order, \
                                        __FILE__, __LINE__);        \
          ((n = interval_generator_next (itree_iter_))              \
           || (interval_tree_iter_finish (itree_iter_), false));)

#define ITREE_FOREACH_ABORT() \
  interval_tree_iter_finish (itree_iter_)

#define ITREE_FOREACH_NARROW(beg, end) \
  interval_generator_narrow (itree_iter_, beg, end)

#endif