#!/usr/bin/env bash
set -uo pipefail

# CASAN Plan-16 SEC-28 (X-04) — path-traversal / symlink guard.
#
# A tool that takes a file path as input/output can be pointed at an arbitrary
# location via `..` or a symlink (e.g. a symlink named "input.txt" -> /etc/passwd),
# reading or writing outside the workspace. This resolves the REAL path (following
# every symlink) and refuses anything that escapes the allowed root.
#
# Usage:  path-guard.sh <path> [allowed-root]     (default root: repo workspace)
# Exit:   0 inside the root, 1 outside / unresolvable.

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
source "$SCRIPT_DIR/casan-paths.sh"
PROJECT_ROOT="$CASAN_APP_ROOT"
PYTHON_BIN="${CASAN_PYTHON_BIN:-}"
if [[ -z "$PYTHON_BIN" ]]; then
  for candidate in /usr/bin/python3 python3 python; do
    if command -v "$candidate" >/dev/null 2>&1 && "$candidate" --version >/dev/null 2>&1; then
      PYTHON_BIN="$candidate"
      break
    fi
  done
fi
[[ -n "$PYTHON_BIN" ]] || { echo "PATH_GUARD_RUNTIME_UNAVAILABLE" >&2; exit 69; }

TARGET="${1:-}"
ROOT="${2:-$PROJECT_ROOT}"
if [[ -z "$TARGET" ]]; then
  echo "Usage: path-guard.sh <path> [allowed-root]" >&2
  exit 64
fi

"$PYTHON_BIN" - "$TARGET" "$ROOT" <<'PY'
import os
import sys

target, root = sys.argv[1], sys.argv[2]
# realpath resolves symlinks in every existing path component and normalizes "..";
# for a not-yet-created leaf it resolves the existing parent chain.
real_target = os.path.realpath(target)
real_root = os.path.realpath(root)

if real_target == real_root or real_target.startswith(real_root + os.sep):
    print(f"PATH_OK {real_target}")
    sys.exit(0)
sys.stderr.write(f"PATH_ESCAPES_ROOT target={target} real={real_target} root={real_root}\n")
sys.exit(1)
PY