"""Request routing and the privilege gate for the central panel (stdlib only).

``route`` is a pure function: it takes the panel context, an HTTP method and a
request target, and returns a ``Response``. Nothing in this module starts a
process, writes a file or opens an outbound connection -- the panel's read-only
claim is structural, not a promise in a comment:

* only ``GET`` and ``HEAD`` are served; every other method is answered with 405
  and a Turkish explanation, never by an action;
* static assets are served from an explicit allow-list, so a request can never
  walk the filesystem (``/static/../server.py`` is a 404);
* an unknown path is a Turkish 404, not a redirect anywhere.

Because ``route`` is pure, tests exercise the whole HTTP surface without binding
a port.
"""

from __future__ import annotations

from dataclasses import dataclass
from pathlib import Path
from urllib.parse import parse_qs, unquote

from . import render
from .fleet_data import FleetSnapshot
from .render import Privilege, ServerInfo

#: Local assets only. Adding a name here is the only way to serve a new file.
STATIC_FILES: dict[str, str] = {
    "tokens.css": "text/css; charset=utf-8",
    "app.css": "text/css; charset=utf-8",
}

READ_METHODS: tuple[str, ...] = ("GET", "HEAD")

#: Response headers that keep an air-gapped panel inert: no script runs, no
#: remote origin is reachable, and the browser is told not to sniff types.
SECURITY_HEADERS: tuple[tuple[str, str], ...] = (
    ("X-Content-Type-Options", "nosniff"),
    ("Referrer-Policy", "no-referrer"),
    (
        "Content-Security-Policy",
        "default-src 'self'; img-src 'self' data:; style-src 'self'; "
        "script-src 'none'; form-action 'self'; base-uri 'none'; frame-ancestors 'none'",
    ),
)


@dataclass(frozen=True)
class Response:
    """One HTTP answer, fully decided before the socket sees it."""

    status: int
    content_type: str
    body: bytes
    content_length: int
    headers: tuple[tuple[str, str], ...] = ()

    @property
    def is_html(self) -> bool:
        return self.content_type.startswith("text/html")


@dataclass(frozen=True)
class PanelContext:
    """Everything a request needs: the snapshot, the privilege level, the facts."""

    snapshot: FleetSnapshot
    privilege: Privilege
    server_info: ServerInfo
    static_dir: Path = render.STATIC_DIR


def route(context: PanelContext, method: str, target: str) -> Response:
    """Decide one request. Pure: same inputs, same bytes, no side effects."""
    verb = (method or "").upper()
    raw_path, _, query_string = target.partition("?")

    if verb not in READ_METHODS:
        return _html(
            405,
            render.render_refused_page(
                verb or "BİLİNMİYOR",
                snapshot=context.snapshot,
                privilege=context.privilege,
                server_info=context.server_info,
            ),
            verb,
            extra_headers=(("Allow", ", ".join(READ_METHODS)),),
        )

    decoded = unquote(raw_path)
    if ".." in decoded or "\x00" in decoded:
        return _not_found(context, decoded, verb)

    params = parse_qs(query_string, keep_blank_values=True)

    if decoded in ("/", "/filo", "/fleet"):
        page = render.render_fleet_page(
            context.snapshot,
            params,
            privilege=context.privilege,
            server_info=context.server_info,
        )
        return _html(200, page, verb)

    if decoded in ("/hakkinda", "/hakkinda/", "/about"):
        page = render.render_about_page(
            context.snapshot,
            privilege=context.privilege,
            server_info=context.server_info,
        )
        return _html(200, page, verb)

    if decoded.startswith("/static/"):
        return _static(context, decoded[len("/static/"):], verb)

    return _not_found(context, decoded, verb)


def _html(
    status: int,
    page: str,
    verb: str,
    *,
    extra_headers: tuple[tuple[str, str], ...] = (),
) -> Response:
    body = page.encode("utf-8")
    headers = SECURITY_HEADERS + (("Cache-Control", "no-store"),) + extra_headers
    if verb == "HEAD":
        return Response(status, "text/html; charset=utf-8", b"", len(body), headers)
    return Response(status, "text/html; charset=utf-8", body, len(body), headers)


def _not_found(context: PanelContext, request_path: str, verb: str) -> Response:
    page = render.render_not_found_page(
        request_path,
        snapshot=context.snapshot,
        privilege=context.privilege,
        server_info=context.server_info,
    )
    return _html(404, page, verb)


def _static(context: PanelContext, name: str, verb: str) -> Response:
    # Allow-list first: anything not named here is a 404, so no path trick can
    # reach a file this panel did not decide to publish.
    content_type = STATIC_FILES.get(name)
    if content_type is None:
        return _not_found(context, f"/static/{name}", verb)

    path = context.static_dir / name
    if not path.is_file():
        return _not_found(context, f"/static/{name}", verb)

    body = path.read_bytes()
    headers = SECURITY_HEADERS + (
        ("Cache-Control", "no-cache"),
    )
    if verb == "HEAD":
        return Response(200, content_type, b"", len(body), headers)
    return Response(200, content_type, body, len(body), headers)