#!/usr/bin/env python3
"""Credential storage for unattended recording.

Secrets live in the Windows Credential Manager (DPAPI, keyed to your Windows
account), not in a file. Nothing here can be committed by accident because
nothing here is written to the repo.

    python creds.py --set-login     store email + password (prompts)
    python creds.py --show          show what is stored (never the password)
    python creds.py --clear         remove everything

What this does and does not protect against:

  DOES  -- plaintext at rest, and the classic "gitignored file gets committed
           after a git add -A" accident.
  DOES  -- readable by another Windows user on this machine.
  NOT   -- a process already running as you. Credential Manager unlocks with
           your login session, so anything running as you can read it. That is
           inherent to unattended operation: a job that logs in without you
           present must be able to reach the secret without you present.

Caveat for Task Scheduler: "Run whether user is logged on or not" runs in a
session where DPAPI may not be able to decrypt these entries. Prefer "Run only
when user is logged on" for any task that needs credentials.

PLATFORM NOTE -- this module is only safe where a real vault backend exists:

  Windows   WinVaultKeyring (Credential Manager, DPAPI).       Good.
  Linux+GUI SecretService (GNOME Keyring / KWallet).           Good.
  Headless  No D-Bus session, no unlocked keyring. `keyring`   NOT SAFE.
  Linux     falls back to a fail or plaintext backend.

On a headless Pi or server, do NOT use this module. Use systemd-creds, which
encrypts to the host/TPM key and is decrypted only for the service:

    systemd-creds encrypt --name=brfc-pass - /etc/credstore.encrypted/brfc-pass
    # then in the unit:  LoadCredential=brfc-pass
    # and read it from:  $CREDENTIALS_DIRECTORY/brfc-pass

Run `python creds.py --check` on each host before trusting it with a secret.
"""
import argparse
import getpass
import sys

try:
    import keyring
except ImportError:
    sys.exit("keyring not installed. Run: pip install keyring")

SERVICE = "brfc-stream-pirate"

# Keys held in the vault.
K_USER = "username"
K_PASS = "password"
K_COOKIE = "session-cookie"     # cached login session, refreshed periodically


def get(key):
    return keyring.get_password(SERVICE, key)


def put(key, value):
    keyring.set_password(SERVICE, key, value)


def drop(key):
    try:
        keyring.delete_password(SERVICE, key)
    except keyring.errors.PasswordDeleteError:
        pass                    # already absent


def load_login():
    """Return (username, password), or None if not configured yet."""
    user, pw = get(K_USER), get(K_PASS)
    return (user, pw) if user and pw else None


def load_cookie():
    """Cached session cookie, or None. Callers must handle it being stale."""
    return get(K_COOKIE)


def save_cookie(value):
    put(K_COOKIE, value)


# Backends that do not actually protect anything. `keyring` selects these
# silently on a headless box, so a secret stored there is effectively plaintext.
UNSAFE_BACKENDS = {"PlaintextKeyring", "Keyring", "fail.Keyring", "EnvironCredential"}


def backend():
    return keyring.get_keyring().__class__.__name__


def backend_is_safe():
    name = backend()
    return name not in UNSAFE_BACKENDS and "fail" not in name.lower()


def _mask(s):
    if not s:
        return "(not set)"
    return s[:2] + "*" * max(0, len(s) - 4) + s[-2:] if len(s) > 4 else "*" * len(s)


def main():
    ap = argparse.ArgumentParser(description=__doc__.splitlines()[0])
    g = ap.add_mutually_exclusive_group(required=True)
    g.add_argument("--set-login", action="store_true", help="store email + password")
    g.add_argument("--show", action="store_true", help="show stored username")
    g.add_argument("--clear", action="store_true", help="remove all stored secrets")
    g.add_argument("--check", action="store_true",
                   help="report whether this host has a real vault backend")
    args = ap.parse_args()

    if args.check:
        name = backend()
        safe = backend_is_safe()
        print(f"backend : {name}")
        print(f"verdict : {'SAFE' if safe else 'NOT SAFE -- do not store secrets here'}")
        if not safe:
            print("          use systemd-creds on this host (see module docstring)")
        sys.exit(0 if safe else 1)

    if not backend_is_safe():
        sys.exit(f"refusing to use backend {backend()!r}: it does not encrypt. "
                 "Run 'python creds.py --check' for guidance.")

    if args.set_login:
        user = input("email: ").strip()
        if not user:
            sys.exit("aborted: empty email")
        pw = getpass.getpass("password: ")
        if not pw:
            sys.exit("aborted: empty password")
        put(K_USER, user)
        put(K_PASS, pw)
        print(f"stored in Windows Credential Manager under '{SERVICE}'")

    elif args.show:
        print(f"service : {SERVICE}")
        print(f"username: {get(K_USER) or '(not set)'}")
        print(f"password: {'(set)' if get(K_PASS) else '(not set)'}")
        print(f"cookie  : {_mask(get(K_COOKIE))}")

    elif args.clear:
        for k in (K_USER, K_PASS, K_COOKIE):
            drop(k)
        print("cleared")


if __name__ == "__main__":
    main()