import mimetypes
import os

from django.http import FileResponse, HttpResponseNotFound
from django.views.decorators.csrf import ensure_csrf_cookie

_FE_DIR_CACHE = None
_INDEX_CACHE = None


def _get_frontend_dir():
    global _FE_DIR_CACHE
    if _FE_DIR_CACHE is None:
        import sys
        if getattr(sys, 'frozen', False):
            _FE_DIR_CACHE = os.path.join(sys._MEIPASS, 'backend', 'static', 'frontend')
        else:
            env_dir = os.environ.get('FRONTEND_DIR')
            if env_dir and os.path.isdir(env_dir):
                _FE_DIR_CACHE = env_dir
            else:
                _FE_DIR_CACHE = os.path.join(
                    os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
                    'static', 'frontend',
                )
    return _FE_DIR_CACHE


def _get_index_path():
    global _INDEX_CACHE
    if _INDEX_CACHE is None:
        p = os.path.join(_get_frontend_dir(), 'index.html')
        _INDEX_CACHE = p if os.path.isfile(p) else ''
    return _INDEX_CACHE


def _serve_file(filepath):
    ct, _ = mimetypes.guess_type(filepath)
    return FileResponse(open(filepath, 'rb'), content_type=ct or 'application/octet-stream')


@ensure_csrf_cookie
def spa_serve(request, path=None):
    """Serve built React assets or fall back to index.html."""
    fdir = _get_frontend_dir()
    req_path = (path or '').lstrip('/')

    if req_path:
        target = os.path.normpath(os.path.join(fdir, req_path))
        if target.startswith(os.path.normpath(fdir)) and os.path.isfile(target):
            return _serve_file(target)

    index = _get_index_path()
    if index:
        return _serve_file(index)
    return HttpResponseNotFound('Frontend not built. Run build.py first.')