from __future__ import annotations

from os import urandom
from threading import Lock

from coincurve._libsecp256k1 import ffi, lib
from coincurve.flags import CONTEXT_FLAGS, CONTEXT_NONE


class Context:
    def __init__(self, seed: bytes | None = None, flag=CONTEXT_NONE, name: str = ""):
        if flag not in CONTEXT_FLAGS:
            msg = f"{flag} is an invalid context flag."
            raise ValueError(msg)
        self._lock = Lock()

        self.ctx = ffi.gc(lib.secp256k1_context_create(flag), lib.secp256k1_context_destroy)
        self.reseed(seed)

        self.name = name

    def reseed(self, seed: bytes | None = None):
        """
        Protects against certain possible future side-channel timing attacks.
        """
        with self._lock:
            seed = urandom(32) if not seed or len(seed) != 32 else seed  # noqa: PLR2004
            res = lib.secp256k1_context_randomize(self.ctx, ffi.new("unsigned char [32]", seed))
            if not res:
                msg = "secp256k1_context_randomize"
                raise ValueError(msg)

    def __repr__(self):
        return self.name or super().__repr__()


GLOBAL_CONTEXT = Context(name="GLOBAL_CONTEXT")