import vpsdk.syscall as _sc
import string


define HEAP_BLOCK_MAGIC = 0x48454150

class _heap_hdr:
    magic:  uint32
    size:   uint32

_heap_inited: int = 0

def _heap_init():
    global _heap_inited
    _heap_inited = 1

export def malloc(size: sizet) -> rawptr:
    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
    # mmap 已按 Linux 六参形态对齐：匿名映射 = fd -1 + MAP_ANONYMOUS + PROT_READ|WRITE
    ptr: uint64 = _sc.mmap(0, uint64(total), uint64(_sc.PROT_READ | _sc.PROT_WRITE),
                           uint64(_sc.MAP_PRIVATE | _sc.MAP_ANONYMOUS), _sc.MMAP_FD_ANON, 0)
    if ptr == 0: return None
    # 块头必须落在**映射区内部**（映射起点 ptr 处），不能写 ptr - hdr_size：
    # 那 8 字节在映射之外 —— 第一次 malloc 时 mmap 返回的正是用户堆起点 0x20000000，
    # 写 0x1ffffff8 就是映射区外 ⇒ #PF(err=0x7 用户态写)，四个 app 启动即崩的现场。
    hdr: _heap_hdr* = _heap_hdr*(uint64(ptr))
    hdr.magic = HEAP_BLOCK_MAGIC
    hdr.size = uint32(size)
    return rawptr(ptr + hdr_size)

export def free(ptr: rawptr):
    if ptr is None: return
    hdr_size: sizet = _heap_hdr.__sizeof__()
    hdr: _heap_hdr* = _heap_hdr*(uint64(ptr) - hdr_size)
    if hdr.magic != HEAP_BLOCK_MAGIC: return

export def calloc(nmemb: sizet, size: sizet) -> rawptr:
    total: sizet = nmemb * size
    p: rawptr = malloc(total)
    if p: string.memset(p, 0, total)
    return p

export def realloc(ptr: rawptr, size: sizet) -> rawptr:
    if ptr is None: return malloc(size)
    if size == 0:
        free(ptr)
        return None
    hdr_size: sizet = _heap_hdr.__sizeof__()
    hdr: _heap_hdr* = _heap_hdr*(uint64(ptr) - hdr_size)
    if hdr.magic != HEAP_BLOCK_MAGIC: return None
    old_size: sizet = hdr.size
    new_ptr: rawptr = 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