from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
from cryptography.hazmat.primitives.ciphers.aead import AESGCM
from cryptography.hazmat.backends import default_backend
import os
import sys

CHUNK = 64 * 1024  # plaintext bytes per chunk (must match src/crypto.ts)


def encrypt(content: bytes, password: str) -> bytes:
    """
    Encrypts the given content using the provided password.

    Uses chunked AES-256-GCM with a PBKDF2-HMAC-SHA512 derived key, matching the
    server/browser implementation in src/crypto.ts.

    Wire format: salt[16] | noncePrefix[7] | encChunk_0 | encChunk_1 | ...
    where encChunk_i = AES-GCM(key, nonce_i, plaintext_i) (16-byte tag appended)
    and nonce_i = noncePrefix[7] || uint32_be(i) || flag, flag=1 on the final
    chunk else 0. Each non-final plaintext chunk is exactly CHUNK bytes.

    Args:
    content (bytes): The content to be encrypted.
    password (str): The password used for encryption.

    Returns:
    bytes: the wire format described above
    """

    # Generate a random nonce prefix and salt
    prefix = os.urandom(7)
    salt = os.urandom(16)

    # Derive a key from the password using PBKDF2
    kdf = PBKDF2HMAC(
        algorithm=hashes.SHA512(),
        length=32,
        salt=salt,
        iterations=210000,
        backend=default_backend()
    )
    aes = AESGCM(kdf.derive(password.encode()))

    # Always emit at least one (possibly empty) final chunk so empty input still
    # round-trips and the final-chunk flag is always present.
    chunks = max(1, -(-len(content) // CHUNK))  # ceil division
    out = bytearray(salt + prefix)
    for i in range(chunks):
        piece = content[i * CHUNK:(i + 1) * CHUNK]
        last = 1 if i == chunks - 1 else 0
        nonce = prefix + i.to_bytes(4, "big") + bytes([last])
        out += aes.encrypt(nonce, piece, None)
    return bytes(out)


if __name__ == "__main__":
    if len(sys.argv) != 4:
        print("Usage: encrypt.py <file> <password> <outfile>")
        sys.exit(1)
    data = encrypt(open(sys.argv[1], "rb").read(), sys.argv[2])
    open(sys.argv[3], "wb").write(data)