from __future__ import annotations

import hashlib
from pathlib import Path

from .constants import FAST_HASH_CHUNK


def fast_hash(path: Path) -> str:
    """Hash size + first/last 64 KiB; used only as a candidate key."""
    size = path.stat().st_size
    with path.open("rb") as f:
        head = f.read(FAST_HASH_CHUNK)
        if size > FAST_HASH_CHUNK:
            f.seek(max(0, size - FAST_HASH_CHUNK))
        tail = f.read(FAST_HASH_CHUNK)
    h = hashlib.sha256()
    h.update(str(size).encode())
    h.update(b"\0")
    h.update(head)
    h.update(b"\0")
    h.update(tail)
    return h.hexdigest()


def sha256(path: Path, chunk_size: int = 1024 * 1024) -> str:
    h = hashlib.sha256()
    with path.open("rb") as f:
        while True:
            chunk = f.read(chunk_size)
            if not chunk:
                break
            h.update(chunk)
    return h.hexdigest()