#ifndef UC_SARENA_H_
#define UC_SARENA_H_

#include <stddef.h>
#include <stdint.h>
#ifdef __cplusplus
extern "C" {
#endif

/** @file
 * Static arena allocator.
 *
 *  An UCSArena allocates memory from pre-existing array
 *
 * The backing array should be suitable aligned to the types
 * that will be allocated from it. Use .e.g
 * @code
 * _Alignas(16) char mem[1024];
 * @endcode
 * as the backing array.
 *
 * Once allocated, a piece of memory obtained from the
 * allocator cannot be free'd individually, only the entire SArena can
 * be free'd/reset
*/
typedef struct UCSArena UCSArena;
struct UCSArena {
    char *start; // start of user buffer
    char *curr;  // next alloc point
    char *end;   // one past end of user buffer
};

/** Initialize a UCSArena with predefined backing array.
 * @data must be an array type
 * Use as
 * @code
 * _Alignas(16) char v[128];
 * SArana a = UC_BV_STATIC_INIT(v);
 * @endcode
 */
#define UC_SAR_STATIC_INIT(data)\
    UC_SAR_INIT((data), sizeof(data))

/** Initialize a UCSArena with predefined memory
 * Use as
 * @code
 * char v[128];
 * SArana a = UC_BV_STATIC_INIT(v, sizeof v);
 * @endcode
 * or
 * @code
 * char *m = malloc(128);
 * SArana a = UC_BV_INIT(m, 128);
 * @endcode
 */
#define UC_SAR_INIT(data, sz)\
    {\
    (data),\
    (data),\
    (data) + sz\
    }

/** Initialize a UCSArena with an array as the backing memory to allocate from.
 * The macro can be used at local scope to allocate memory automatic (stack) storage,
 * or at global scope where the backing array will have static storage duration
 *
 * Use as:
 * @code
 * UC_SAR_ALLOC_DEF(my_allocator, 1024)
 * struct foo *foo = uc_sar_alloc(&my_allocator);
 * if (foo == NULL) {
 *     // out of memory
 * }
 * @endcode
 *
 * @note, the backing store has alignment of 16. Use manual init if a different alignment
 * is needed.
 * @param var_name Variable name for the allocator
 * @param size_  byte size of the backing array
*/
#define UC_SAR_ALLOC_DEF(var_name, size_) \
    struct {\
        _Alignas(16) char memory[size_]; \
    } var_name ## _memory;\
    UCSArena var_name = UC_SAR_STATIC_INIT(var_name ## _memory.memory)

/** Allocate space for @type_ , returned memory is aligned to requirements
 * of @type.
 *
 * Use as:
 * @code
 * UC_SAR_ALLOC_DEF(my_allocator, 1024)
 * struct foo *foo = UC_SAR_ALLOC_ALIGNED(&my_allocator, struct foo);
 * // Array types can be used too, room for null terminated string of lengh 10:
 * char *str = UC_SAR_ALLOC_ALIGNED(&my_allocator, char[11]);
 * @endcode
 */
#define UC_SAR_ALLOC_ALIGNED(allocator, type_) \
    uc_sar_alloc_aligned((allocator), sizeof (type_), _Alignof(type_))

// Allocate @sz bytes from the UCSArena. Returns NULL if not enough space
void *uc_sar_alloc(UCSArena *a, size_t sz);

// Allocate @sz bytes from the UCSArena, returned pointer is aligned to @align
// Returns NULL if not enough space
void *uc_sar_alloc_aligned(UCSArena *a, size_t sz, unsigned int align);

static inline void uc_sar_reset(UCSArena *a)
{
    a->curr = a->start;
}
#ifdef __cplusplus
}
#endif

#endif