"""Small web adapters, owned by this project; synchronous work retains its slot."""

import threading
from contextlib import contextmanager
from pathlib import Path

from fastapi import HTTPException
from fastapi.responses import JSONResponse
from fastapi.staticfiles import StaticFiles


class Busy(HTTPException):
    def __init__(self):
        super().__init__(
            429, "The workspace is busy. Wait a moment and try again.", headers={"Retry-After": "5"}
        )


class Admission:
    def __init__(self, active, waiting):
        self.capacity = active
        self.maximum = active + waiting
        self.total = 0
        self.running = 0
        self.condition = threading.Condition()

    @contextmanager
    def slot(self):
        with self.condition:
            if self.total >= self.maximum:
                raise Busy()
            self.total += 1
            self.condition.notify_all()
            if not self.condition.wait_for(lambda: self.running < self.capacity, timeout=60):
                self.total -= 1
                self.condition.notify_all()
                raise Busy()
            self.running += 1
        try:
            yield
        finally:
            with self.condition:
                self.running -= 1
                self.total -= 1
                self.condition.notify_all()


def limit_body(app, maximum):
    @app.middleware("http")
    async def bounded_body(request, call_next):
        if request.method in {"POST", "PUT"}:
            data = bytearray()
            async for chunk in request.stream():
                data.extend(chunk)
                if len(data) > maximum:
                    return JSONResponse(
                        {"detail": "Request exceeds the upload limit."}, status_code=413
                    )
            request._body = bytes(data)
        response = await call_next(request)
        response.headers["X-Content-Type-Options"] = "nosniff"
        if request.url.path.startswith("/api/"):
            response.headers["Cache-Control"] = "no-store"
        return response


def mount_frontend(app):
    static = Path(__file__).parent / "static"
    if not (static / "index.html").exists():

        @app.get("/")
        def missing_build():
            return JSONResponse(
                {"detail": "Frontend not built. Run npm ci and npm run build in frontend/."},
                status_code=503,
            )
    else:
        app.mount("/", StaticFiles(directory=static, html=True), name="frontend")