#!/usr/bin/env python3
# Gate for acp-bridge-listen.sh's socat listeners: reads exactly one line
# (unbuffered — a normal buffered readline could silently swallow bytes
# belonging to the real protocol stream that follows, which would be lost on
# exec) from the connection and compares it to PEER_BRIDGE_TOKEN. Only on a
# match does it exec into the real target, inheriting the same socket fds so
# everything after the token line passes through untouched.
#
# Without this, acp-bridge-listen.sh's ACP port would be a fully
# auto-approving agent shell (bash, edit, write) reachable, unauthenticated,
# by anything on the same docker network — not just the specific peer
# workspace it's meant for.
import os
import sys


def read_line_unbuffered():
    buf = b""
    fd = sys.stdin.fileno()
    while True:
        b = os.read(fd, 1)
        if not b or b == b"\n":
            break
        buf += b
    return buf.decode(errors="replace")


def main():
    if len(sys.argv) < 2:
        print("usage: acp-bridge-auth.py <command> [args...]", file=sys.stderr)
        print("       acp-bridge-auth.py --print-env <VAR_NAME>", file=sys.stderr)
        sys.exit(1)

    expected = os.environ.get("PEER_BRIDGE_TOKEN", "")
    got = read_line_unbuffered()
    if not expected or got != expected:
        sys.exit(1)

    # --print-env avoids threading a shell one-liner through socat's own EXEC
    # argument quoting just to echo an already-inherited env var.
    if sys.argv[1] == "--print-env":
        print(os.environ.get(sys.argv[2], ""))
        sys.exit(0)

    os.execvp(sys.argv[1], sys.argv[1:])


if __name__ == "__main__":
    main()