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"""Serves a static frontend alongside the Trackio HTTP API."""

import hashlib
import json
import logging
import re
from pathlib import Path

from starlette.middleware.base import BaseHTTPMiddleware
from starlette.responses import FileResponse, HTMLResponse, JSONResponse
from starlette.routing import Mount, Route, get_route_path
from starlette.staticfiles import StaticFiles

ASSETS_DIR = Path(__file__).parent / "assets"

_logger = logging.getLogger(__name__)

_ABSOLUTE_REF_RE = re.compile(r'(href|src)="(/(?:assets|static/trackio)/[^"]+)"')

_LIVE_RELOAD_SCRIPT = """
<script>
(() => {
  const endpoint = "__TRACKIO_ROOT_PATH__/__trackio/frontend_version";
  let currentVersion = null;

  async function poll() {
    try {
      const response = await fetch(endpoint, { cache: "no-store" });
      const payload = await response.json();
      if (currentVersion === null) {
        currentVersion = payload.version;
        return;
      }
      if (payload.version !== currentVersion) {
        window.location.reload();
      }
    } catch (error) {
      console.warn("Trackio live reload poll failed", error);
    }
  }

  poll();
  setInterval(poll, 1000);
})();
</script>
""".strip()


def _frontend_version(frontend_root: Path) -> str:
    digest = hashlib.sha256()
    for path in sorted(frontend_root.rglob("*")):
        if not path.is_file():
            continue
        relative = path.relative_to(frontend_root)
        digest.update(str(relative).encode("utf-8"))
        stat = path.stat()
        digest.update(str(stat.st_mtime_ns).encode("utf-8"))
        digest.update(str(stat.st_size).encode("utf-8"))
    return digest.hexdigest()


def _inject_live_reload(html: str, root_path: str) -> str:
    if "/__trackio/frontend_version" in html:
        return html
    script = _LIVE_RELOAD_SCRIPT.replace("__TRACKIO_ROOT_PATH__", root_path)
    if "</body>" in html:
        return html.replace("</body>", f"{script}\n  </body>")
    return html + script


def _prefix_absolute_refs(html: str, root_path: str) -> str:
    if not root_path:
        return html
    return _ABSOLUTE_REF_RE.sub(
        lambda m: f'{m.group(1)}="{root_path}{m.group(2)}"', html
    )


def _inject_base_script(html: str, root_path: str) -> str:
    if not root_path:
        return html
    script = f"<script>window.__trackio_base = {json.dumps(root_path)};</script>"
    if "<head>" in html:
        return html.replace("<head>", f"<head>\n    {script}", 1)
    return script + html


def _render_index_html(path: Path, root_path: str = "") -> str:
    html = path.read_text(encoding="utf-8")
    html = _prefix_absolute_refs(html, root_path)
    html = _inject_base_script(html, root_path)
    return _inject_live_reload(html, root_path)


def _html_response(path: Path, root_path: str = "") -> HTMLResponse:
    return HTMLResponse(_render_index_html(path, root_path))


class FrontendMiddleware(BaseHTTPMiddleware):
    def __init__(self, app, frontend_root: Path, index_html_path: Path):
        super().__init__(app)
        self.frontend_root = frontend_root
        self.index_html_path = index_html_path
        self.reserved_prefixes = (
            "/api/",
            "/file",
            "/version",
            "/artifact_blob/",
            "/static/trackio",
            "/__trackio/frontend_version",
            "/oauth/",
            "/login/",
            "/mcp",
        )
        self.reserved_exact = {
            "/api",
            "/oauth",
            "/login",
        }

    async def dispatch(self, request, call_next):
        if request.method not in {"GET", "HEAD"}:
            return await call_next(request)

        path = get_route_path(request.scope)
        if path in self.reserved_exact or path.startswith(self.reserved_prefixes):
            return await call_next(request)

        root_path = request.scope.get("root_path", "")
        relative_path = path.lstrip("/")
        requested_path = (self.frontend_root / relative_path).resolve()
        if (
            relative_path
            and requested_path.is_file()
            and requested_path.is_relative_to(self.frontend_root)
        ):
            if requested_path.suffix.lower() == ".html":
                return _html_response(requested_path, root_path)
            return FileResponse(requested_path)

        return _html_response(self.index_html_path, root_path)


def mount_frontend(app, frontend_dir: str | Path):
    frontend_root = Path(frontend_dir).resolve()
    if not frontend_root.exists():
        _logger.warning(
            "Trackio dashboard UI was not mounted: %s is missing. "
            "Build the frontend or provide a custom frontend directory.",
            frontend_root,
        )
        return

    index_html_path = frontend_root / "index.html"
    if not index_html_path.exists():
        _logger.warning(
            "Trackio dashboard UI was not mounted: %s is missing.",
            index_html_path,
        )
        return

    async def frontend_version(_request):
        return JSONResponse({"version": _frontend_version(frontend_root)})

    static_assets = StaticFiles(directory=str(ASSETS_DIR))

    app.add_middleware(
        FrontendMiddleware,
        frontend_root=frontend_root,
        index_html_path=index_html_path,
    )
    app.routes.append(Mount("/static/trackio", app=static_assets))
    app.routes.append(
        Route("/__trackio/frontend_version", frontend_version, methods=["GET"])
    )