#!/usr/bin/env python3
"""Generate src/hmac_key.h with a random 32-byte HMAC-SHA256 key.

Usage:
    python3 tools/generate_hmac_key.py

This creates src/hmac_key.h (gitignored) and prints the hex key to stdout.
The hex key should be entered in the Android app's Settings screen.
"""
import os
import sys
import binascii

KEY_LENGTH = 32
OUTPUT_FILE = os.path.join("src", "hmac_key.h")


def generate():
    key = os.urandom(KEY_LENGTH)
    hex_key = binascii.hexlify(key).decode().upper()

    header = f"""#ifndef HMAC_KEY_H
#define HMAC_KEY_H

// AUTO-GENERATED by tools/generate_hmac_key.py
// Do NOT commit this file. Do NOT edit by hand.
// To regenerate: python3 tools/generate_hmac_key.py

const uint8_t HMAC_KEY[{KEY_LENGTH}] = {{
    {', '.join(f'0x{b:02x}' for b in key)}
}};

#endif // HMAC_KEY_H
"""

    os.makedirs("src", exist_ok=True)
    with open(OUTPUT_FILE, "w") as f:
        f.write(header)

    print(f"HMAC key written to {OUTPUT_FILE}")
    print(f"Enter this key in the Android app Settings:")
    print(f"  {hex_key}")
    print()
    print(f"ESP serial output after boot will show the same key.")


if __name__ == "__main__":
    if os.path.exists(OUTPUT_FILE):
        overwrite = input(f"{OUTPUT_FILE} already exists. Overwrite? [y/N] ")
        if overwrite.lower() != 'y':
            print("Aborted.")
            sys.exit(0)
    generate()