/* Copyright (C) 2025 Aryadev Chavali

 * 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 Version 2 for
 * details.

 * You may distribute and modify this code under the terms of the GNU General
 * Public License Version 2, which you should have received a copy of along with
 * this program.  If not, please go to <https://www.gnu.org/licenses/>.

 * Created: 2025-04-06
 * Description:
 */

#ifndef TAG_H
#define TAG_H

#include <base.h>

#include <stdbool.h>
#include <stdlib.h>

// Opaque structure to make tagged pointers a separate type from general
// pointers
typedef struct Obj lisp_t;

#define NIL NULL

enum Tag
{
  TAG_NIL   = 0b00000000, // Atomic types
  TAG_INT   = 0b00000001, // special so we can encode 63 bit integers
  TAG_SYM   = 0b00000100,
  TAG_SSYM  = 0b00001000,
  TAG_CHAR  = 0b00001100,
  TAG_BOOL  = 0b00010000,
  TAG_FLOAT = 0b00010100,
  TAG_CONS  = 0b00000010, // Container types
  TAG_VEC   = 0b00000110,
  TAG_STR   = 0b00001010,

  NUM_TAGS = 9,
};

enum Shift
{
  SHIFT_INT   = 1,
  SHIFT_SSYM  = 5,
  SHIFT_CHAR  = 8,
  SHIFT_SYM   = 8,
  SHIFT_BOOL  = 8,
  SHIFT_FLOAT = 8,

  SHIFT_CONS = 8,
  SHIFT_VEC  = 8,
  SHIFT_STR  = 8,
};

enum Mask
{
  MASK_INT   = 0b00000001,
  MASK_SSYM  = 0b00011111,
  MASK_SYM   = 0b11111111,
  MASK_CHAR  = 0b11111111,
  MASK_BOOL  = 0b11111111,
  MASK_FLOAT = 0b11111111,

  MASK_CONS = 0b11111111,
  MASK_VEC  = 0b11111111,
  MASK_STR  = 0b11111111,
};

#define TAG(PTR, TYPE)    ((lisp_t *)(((PTR) << SHIFT_##TYPE) | TAG_##TYPE))
#define IS_TAG(PTR, TYPE) (((u64)(PTR) & MASK_##TYPE) == TAG_##TYPE)
#define UNTAG(PTR, TYPE)  (((u64)PTR) >> SHIFT_##TYPE)

enum Tag tag_get(lisp_t *ptr);

lisp_t *tag_int(i64 i);
lisp_t *tag_char(u32 codepoint);
lisp_t *tag_sym(void *ptr);
lisp_t *tag_ssym(const char *data, size_t size);
lisp_t *tag_bool(bool b);
lisp_t *tag_vec(void *ptr);
lisp_t *tag_str(void *ptr);
lisp_t *tag_cons(void *ptr);

#define INT_MAX ((1L << 62) - 1)
#define INT_MIN (-(1L << 62))

#endif