from __future__ import annotations

import re
from pathlib import Path

from fastapi.staticfiles import StaticFiles
from starlette.responses import Response
from starlette.types import Scope

HTML_NO_STORE = "no-store"
HASHED_ASSET_IMMUTABLE = "public, max-age=31536000, immutable"

_MODULE_SCRIPT = re.compile(
    r'<script\b[^>]*\bsrc=["\'](?P<src>/assets/[^"\']+)["\'][^>]*>',
    re.IGNORECASE,
)
_HASHED_ASSET = re.compile(
    r"^assets/(?:.+)-[A-Za-z0-9_-]{8,}\.[A-Za-z0-9]+$",
)


def frontend_build_id(frontend_root: Path) -> str | None:
    """Return the exact content-hashed module loaded by the current index."""

    try:
        index = (frontend_root / "index.html").read_text(encoding="utf-8")
    except OSError:
        return None
    for match in _MODULE_SCRIPT.finditer(index):
        source = match.group("src")
        if _HASHED_ASSET.fullmatch(source.removeprefix("/")):
            return source
    return None


class ControlStationStaticFiles(StaticFiles):
    """Serve the SPA shell fresh while retaining immutable hashed assets."""

    async def get_response(self, path: str, scope: Scope) -> Response:
        response = await super().get_response(path, scope)
        if response.status_code >= 400:
            return response
        content_type = response.headers.get("content-type", "").lower()
        normalized = path.lstrip("/")
        if content_type.startswith("text/html"):
            response.headers["Cache-Control"] = HTML_NO_STORE
        elif _HASHED_ASSET.fullmatch(normalized):
            response.headers["Cache-Control"] = HASHED_ASSET_IMMUTABLE
        return response