import vpsdk.syscall as _sc
import string
import t, c

define HEAP_BLOCK_MAGIC = 0x48454150

@t.Object
class _heap_hdr:
    magic:  uint32
    size:   uint32

_heap_inited: int = 0

def _heap_init():
    global _heap_inited
    _heap_inited = 1

def malloc(size: sizet) -> t.CPtr | t.CExport:
    global _heap_inited
    if size == 0: return None
    if _heap_inited == 0:
        _heap_init()
    hdr_size: sizet = _heap_hdr.__sizeof__()
    total: sizet = hdr_size + size
    ptr: uint64 = _sc._syscall1(uint64(_sc.SYSCALL_MMAP), uint64(total))
    if ptr == 0: return None
    hdr: _heap_hdr* = t.CPtr(ptr)
    hdr.magic = HEAP_BLOCK_MAGIC
    hdr.size = uint32(size)
    return t.CPtr(ptr + hdr_size)

def free(ptr: t.CPtr) -> t.CExport:
    if ptr is None: return
    hdr_size: sizet = _heap_hdr.__sizeof__()
    hdr: _heap_hdr* = t.CPtr(uint64(ptr) - hdr_size)
    if hdr.magic != HEAP_BLOCK_MAGIC: return

def calloc(nmemb: sizet, size: sizet) -> t.CPtr | t.CExport:
    total: sizet = nmemb * size
    p: t.CPtr = malloc(total)
    if p:
        string.memset(p, 0, total)
    return p

def realloc(ptr: t.CPtr, size: sizet) -> t.CPtr | t.CExport:
    if ptr is None: return malloc(size)
    if size == 0:
        free(ptr)
        return None
    hdr_size: sizet = _heap_hdr.__sizeof__()
    hdr: _heap_hdr* = t.CPtr(uint64(ptr) - hdr_size)
    if hdr.magic != HEAP_BLOCK_MAGIC: return None
    old_size: sizet = hdr.size
    new_ptr: t.CPtr = malloc(size)
    if new_ptr is None: return None
    copy_size: sizet = old_size if old_size < size else size
    string.memcpy(new_ptr, ptr, copy_size)
    free(ptr)
    return new_ptr