"""Gradio Server assembly.

Builds the ``gradio.Server`` (FastAPI-style API through Gradio), registers the
backend endpoints, and serves the **custom HTML/JS frontend** at the site root.

The frontend (``src/frontend/index.html`` + ``static/``) is a hand-authored
single-page app — onboarding wizard → salary dashboard → contextual rights chat —
that calls the registered ``@app.api`` endpoints (``/dashboard``, ``/chat``,
``/parse_lonstatistik``) via the Gradio JS client. This is the "off-brand" custom
UI; Gradio's own theming is not used here.

See: https://huggingface.co/blog/introducing-gradio-server
"""

from __future__ import annotations

from pathlib import Path

from fastapi.responses import FileResponse
from fastapi.staticfiles import StaticFiles
from gradio import Server

from .api.endpoints import register

# src/frontend/{index.html, static/}
FRONTEND = Path(__file__).resolve().parents[1] / "frontend"
INDEX_HTML = FRONTEND / "index.html"
STATIC_DIR = FRONTEND / "static"


def build_server() -> Server:
    """Create the configured Gradio Server with the custom frontend at ``/``."""
    app = Server()

    # Backend API endpoints (queue-managed, gradio_client / JS-client compatible).
    register(app)

    # Serve the custom single-page frontend. The Gradio JS client connects to the
    # same origin and calls the registered API endpoints by name.
    app.mount("/static", StaticFiles(directory=str(STATIC_DIR)), name="static")

    @app.get("/")
    def _index() -> FileResponse:  # noqa: D401 — serves the SPA shell
        return FileResponse(str(INDEX_HTML))

    return app