import hashlib

import binascii


class HashDerivedKey:

    @staticmethod
    def from_hex(hex_str):
        return HashDerivedKey(bytes(bytearray.fromhex(hex_str)))

    def __init__(self, master):
        def ensure_bytes(b):
            assert isinstance(b, bytes)
            return b
        ensure_bytes(master)

        def derive(seed):
            ensure_bytes(seed)
            sha = hashlib.sha256()
            sha.update(master)
            sha.update(seed)
            return sha.digest()

        def hex(b): return binascii.hexlify(b).decode("utf-8")
        self.master = master
        self.master_hex = lambda: hex(master)
        self.derive = derive
        self.derive_hex = lambda seed: hex(derive(seed))

    def derive_metadata(self, seed):
        key = self.derive(seed)
        return (key, {"key_seed": binascii.hexlify(seed).decode("utf-8")})