#!/bin/bash
# import-bluez-bond.sh — share a BlueZ (Linux) Bluetooth pairing with MontaukOS.
#
# Dual-boot problem: the AX211's BD_ADDR override (0xFC31) is cosmetic — the
# baseband keeps answering pages on the FACTORY address, so a peer (headset)
# sees Linux and MontaukOS as ONE device with ONE link-key slot.  Each OS
# pairing clobbers the key the other OS depends on, and every reconnect from
# the other OS then dies with Authentication Failure (reason 0x05).
#
# Fix: both OSes share the SAME identity and the SAME link key.  This script
# copies a BlueZ link key into MontaukOS's key store (os/btkeys.bin on the
# installed root) and pins MontaukOS's configured MAC to the adapter's factory
# address so the app reports the identity actually used on air.
#
# Usage:
#   sudo ./scripts/import-bluez-bond.sh <montauk-root-mount> <device-mac> [adapter-mac] [--reverse-key]
#
# Example:
#   sudo ./scripts/import-bluez-bond.sh /run/media/$USER/<uuid> E4:58:BC:5F:E0:30
#
# --reverse-key: byte-swap the key (fallback if authentication still fails).
#
# NOTE: replaces the MontaukOS key store with this single bond.  Re-pair other
# devices from MontaukOS afterwards if you had more.

set -euo pipefail

if [ "$(id -u)" -ne 0 ]; then
    echo "error: must run as root (reads /var/lib/bluetooth)" >&2
    exit 1
fi

TARGET="${1:?usage: import-bluez-bond.sh <montauk-root-mount> <device-mac> [adapter-mac] [--reverse-key]}"
DEVICE="${2:?missing device MAC}"
ADAPTER="${3:-}"
REVERSE=0
for arg in "$@"; do [ "$arg" = "--reverse-key" ] && REVERSE=1; done
[ "$ADAPTER" = "--reverse-key" ] && ADAPTER=""

DEVICE="${DEVICE^^}"

# Auto-detect the adapter: the directory under /var/lib/bluetooth that holds
# this device, preferring a factory (not locally-administered "x2:") address.
if [ -z "$ADAPTER" ]; then
    for dir in /var/lib/bluetooth/*/; do
        a="$(basename "$dir")"
        [ -f "/var/lib/bluetooth/$a/$DEVICE/info" ] || continue
        if [ -z "$ADAPTER" ] || [[ "${ADAPTER:1:1}" == "2" && "${a:1:1}" != "2" ]]; then
            ADAPTER="$a"
        fi
    done
fi
[ -n "$ADAPTER" ] || { echo "error: no adapter dir holds a bond for $DEVICE" >&2; exit 1; }

INFO="/var/lib/bluetooth/$ADAPTER/$DEVICE/info"
[ -f "$INFO" ] || { echo "error: $INFO not found" >&2; exit 1; }
KEY="$(sed -n '/^\[LinkKey\]/,/^\[/{s/^Key=//p}' "$INFO" | head -1)"
[ -n "$KEY" ] || { echo "error: no [LinkKey] Key= in $INFO" >&2; exit 1; }

[ -d "$TARGET/os" ] || { echo "error: $TARGET/os missing — is the MontaukOS root mounted there?" >&2; exit 1; }

echo "adapter (factory identity): $ADAPTER"
echo "device:                     $DEVICE"
echo "key:                        ${KEY:0:4}... (${#KEY} hex chars)"

python3 - "$TARGET/os/btkeys.bin" "$DEVICE" "$KEY" "$REVERSE" <<'EOF'
import sys
path, device, keyhex, reverse = sys.argv[1], sys.argv[2], sys.argv[3], int(sys.argv[4])

# MontaukOS on-disk layout (kernel Hci.cpp): 'BTK1' + 8 x { addr[6], key[16], valid[1] }.
# addr is stored LSB-first (HCI wire order); BlueZ's hex key is already in HCI order.
addr = bytes(int(b, 16) for b in reversed(device.split(":")))
key = bytes.fromhex(keyhex)
assert len(key) == 16, "link key must be 16 bytes"
if reverse:
    key = key[::-1]

blob = bytearray(b"BTK1")
blob += addr + key + b"\x01"          # slot 0: the imported bond
blob += b"\x00" * 23 * 7              # slots 1..7 empty
with open(path, "wb") as f:
    f.write(blob)
print(f"wrote {path} ({len(blob)} bytes, 1 bond)")
EOF

# Pin the configured MAC to the factory address (truthful display; the 0xFC31
# override is cosmetic on this hardware anyway).
CONF="$TARGET/config/bluetooth.toml"
mkdir -p "$TARGET/config"
if [ -f "$CONF" ] && grep -q '^ *mac *=' "$CONF"; then
    sed -i "s/^ *mac *=.*/mac = \"$ADAPTER\"/" "$CONF"
else
    printf 'mac = "%s"\n' "$ADAPTER" >> "$CONF"
fi
echo "set $CONF mac = $ADAPTER"
echo "done — boot MontaukOS; the device should reconnect without re-pairing."