#ifndef UNIVERSAL_SERVICE_H
#define UNIVERSAL_SERVICE_H
/* Copyright (C) 2024 Peter McGoron
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, 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 Lesser General Public
 * License along with this program. If not, see
 * <https://www.gnu.org/licenses/>.
*/

#include <stddef.h>

/********************************
 * Compatability stuff.
 ********************************/
#if __STDC_VERSION__ >= 199101L
# define UNS_INLINE inline
# include <stdint.h>
#else
# define UNS_INLINE
# define SIZE_MAX ((size_t)0 - 1)
#endif

#if defined(__GNUC__)
# define UNS_UNUSED __attribute__((unused))
#else
# define UNS_UNUSED
#endif

#if !defined(UNS_WORD) && __STDC_VERSION__ >= 199101L
# include <stdint.h>
# include <limits.h>
# define UNS_WORD uintptr_t
# define UNS_SIGNED_WORD intptr_t
# define UNS_WORD_MAX UINTPTR_MAX
# define UNS_SWORD_MAX INTPTR_MAX
# define UNS_SWORD_MIN INTPTR_MIN
#elif !defined(UNS_WORD)
# include <limits.h>
# define UNS_WORD unsigned long
# define UNS_WORD_MAX ULONG_MAX
# define UNS_SIGNED_WORD long
# define UNS_SWORD_MAX LONG_MAX
# define UNS_SWORD_MIN LONG_MIN
#endif

typedef UNS_WORD uns_word;
typedef UNS_SIGNED_WORD uns_sword;

/** Type for a pointer to a region.
  *
  * This struct doesn't exist and is used to make a unique pointer for
  * type checking.
  *
  * This pointer must be what was returned from an allocation (i.e. it
  * points to the first byte but before any hidden header data).
 */
typedef struct uns_ptr *Uns_ptr;

/** Flags for bytes regions. */
enum uns_bytes_type {
	UNS_NOEXEC = 0
};

/** Flags for record regions. */
enum uns_record_type {
	UNS_POINTERS_ONLY = 0
};

/** Type of a value in a record. */
enum uns_fld_type {
	UNS_POINTER,
	UNS_INTEGER,

	/** Value is a weak pointer. */
	UNS_WEAK
};

/** Container that boxes pointers for the runtime.
  *
  * Used for
  *
  * 1) Store roots of the GC,
  * 2) Store GC pointers used in C and possibly not pointed-to anywhere
  *    else in GC space,
  * 3) Preserve the location of a pointer after it moves.
  */
struct uns_ctr {
	 /** Pointer to a region in the heap, or NULL.
	   *
	   * All roots must point into the same heap, or to NULL.
	   * Multiple roots are allowed to point to the same region.
	   */
	void *p;

	/** This field is managed by the library.
	  * This must be set to NULL when initializing the container and
	  * must not be touched while the container is in the root list.
	  */
	struct uns_ctr *prev; 

	/** This field is managed by the library.
	  * This must be set to NULL when initializing the container and
	  * must not be touched while the container is in the root list.
	  */
	struct uns_ctr *next;
};

/** Opaque struct that stores the state of a garbage collected heap.
  *
  * The only thing that is stable about the layout of this struct is
  * that the first field is ALWAYS a pointer to the collector context.
  *
  * The context pointer will always be the same pointer from init to
  * deinit.
  */
typedef struct uns_gc *Uns_GC;

/** Size of `struct uns_gc` for allocation. */
extern const size_t uns_gc_size;

/** Get the context pointer for the collector. */
UNS_UNUSED static UNS_INLINE void *uns_ctx(Uns_GC gc)
{
	return *((void **)gc);
}

/** Set the context pointer for the collector. */
UNS_UNUSED static UNS_INLINE void uns_set_ctx(Uns_GC gc, void *ctx)
{
	*((void **)gc) = ctx;
}

/** Zero the memory of the generic GC struct. This will leak
  * memory if a collector was initialized and not deinitialized
  * beforehand.
  *
  * This must be called when the structure is allocated.
  */
void uns_gc_zero(Uns_GC gc);

/** Free memory associated with the GC. It is OK to call this
  * with a GC that has not been initialized.
  */
void uns_deinit(Uns_GC gc);

/** Set deinit function. */
void uns_set_deinit(Uns_GC gc, void(*deinit)(Uns_GC));

/** Set OOM handler. */
void uns_set_oom(Uns_GC gc, void(*oom)(Uns_GC));

/** Call OOM handler. */
void uns_on_oom(Uns_GC gc);

/** Set garbage collection function. */
void uns_set_collect(Uns_GC gc, int(*collect)(Uns_GC));

/** Set allocation function. */
void uns_set_alloc(Uns_GC gc,
                   void*(*alloc)(Uns_GC, size_t, enum uns_bytes_type));

/** Set allocation function. */
void uns_set_alloc_rec(Uns_GC gc,
                       void*(*alloc_rec)(Uns_GC, size_t, enum uns_record_type));

/** Set record setter function. */
void uns_set_set(Uns_GC gc, void(*set)(Uns_ptr, size_t, enum uns_fld_type,
                                       void*));

/** Set record getter function. */
void uns_set_get(Uns_GC gc, void*(*get)(Uns_ptr, size_t,
                                        enum uns_fld_type *));

/** Force a collection. */
int uns_collect(Uns_GC gc);

/** Allocate a region of bytes.
  *
  * This function will only return NULL if:
  *
  * 1. The type of region requested in `typ` is not supported, or
  * 2. The collector ran out of memory and the out-of-memory handler
  *    did not exit the program.
  *
  * Results are undefined if the type is not supported, but all
  * allocators can be compiled with a mode to abort in those cases.
  */
void *uns_alloc(Uns_GC gc, size_t bytes, enum uns_bytes_type typ);

/** Allocate a record.
  *
  * This function will only return NULL if:
  *
  * 1. The type of region requested in `typ` is not supported, or
  * 2. The collector ran out of memory and the out-of-memory handler
  *    did not exit the program.
  *
  * `len` is the number of elements in the record.
  */
void *uns_alloc_rec(Uns_GC gc, size_t len, enum uns_record_type typ);

/** Free a region.
  *
  * This is a no-op if freeing is not supported by the collector, or
  * if `p` is NULL.
  */
void uns_free(Uns_GC gc, Uns_ptr p);

/** Get a field from a record.
  *
  * ## Parameters
  * - `notnull gc`: GC data.
  * - `notnull rec`: Pointer to a record.
  * - `ind`: Index of the field in the record. This is not the byte
  *   offset.
  * - `out typ`: What type of field (integer, weak, etc.) was contained
  *   in the field. May be NULL.
  */
void *uns_get(Uns_GC gc, Uns_ptr rec, size_t ind, enum uns_fld_type *typ);

/** Set a field in a record.
  *
  * ## Parameters
  * - `notnull gc`: GC Data.
  * - `notnull rec`: Pointer to a record.
  * - `ind`: Index of the field in the record. This is not the byte
  *   offset.
  * - `typ`: The type of record to store. Behavior is undefined if the
  *   field type is not supported, either by the record or by the heap.
  * - `val`: Value to store.
  */
void uns_set(Uns_GC gc, Uns_ptr rec, size_t ind, enum uns_fld_type typ, 
             void *val);

/** Add a root to the GC.
  *
  * ## Parameters
  * - `notnull gc`: GC data.
  * - `notnull in out root`: Pointer to the container containing the root.
  *   Do not modify any other field in the container, except for p, after
  *   this function returns.
  */
void uns_root_add(Uns_GC gc, struct uns_ctr *root);

/** Remove a root from the GC.
  *
  * ## Parameters
  * - `notnull gc`: GC data.
  * - `notnull in out root`: Pointer to the container containing the
  *    root to be removed. If the root is not a part of any heap (the
  *    prev and next pointers are NULL), then this function is a noop.
  *    This function does not modify p.
  */
void uns_root_remove(Uns_GC gc, struct uns_ctr *root);

/** Get the head of the roots list.
  */
struct uns_ctr *uns_roots(Uns_GC gc);

#endif