#pragma once
#include "core.h"

// Internal header added in front of each allocation
typedef struct LBlockHeader LBlockHeader;
struct LBlockHeader {
    U32 next;            // offset from base
    U32 prev;            // offset from base
    U32 size_and_flags;  // size | free_bit
    // Padding to ensure we always return 16 byte aligned pointers.
    uint8_t pad[4];
};
_Static_assert(sizeof(LBlockHeader) == 16, "sizeof(BlockHeader) is not 16");

/**
 * General purpose allocator from a pre-defined backing store
 * - Allocated pointers are aligned to 16 bytes.
 * - Backing buffer must be aligned to 16 bytes
 * - 4Gb - 16 is max for the allocator backing buffer.
 * - Allocation of > 0 bytes returns a size aligned up to 16 bytes
 * - Allocation of 0 bytes returns a valid pointer with 0 usable space
 * The allocator maintains a doubly linked list of blocks,
 * when blocks are free'd, adjacent blocks are merged to keep.
 * This is also known as a buddy allocator
 * fragmentation to a minimum
 */
typedef struct LAlloc LAlloc;
struct LAlloc {
    uint8_t *base;              // backing store
    U32 size;                   // total size
    LBlockHeader *next_alloc;   // start of free block search
};

void lalloc_init(LAlloc *allocator, void *backing_store, U32 size);

void *lalloc(LAlloc *allocator, U32 size);
void lfree(LAlloc *allocator, void *ptr);

LBlockHeader *lblock_from_offset(const LAlloc *allocator, U32 offset);
U32 lblock_size(const LBlockHeader *block);
int lblock_is_free(const LBlockHeader *block);