"""Write/remove per-route Traefik dynamic-config files.

Mirrors furtka/furtka/https.py's snippet-write pattern: write to a temp
file, then atomically rename over the target, so Traefik's file provider
never observes a half-written route. Unlike https.py's Caddy target, no
reload call is needed here — Traefik's file provider hot-reloads on change.

Config is built with plain string formatting rather than a YAML library,
to keep the control-plane's dependency footprint at zero (stdlib only, the
same choice the rest of this repo makes) — the shape here is small and
fixed enough that hand-formatting is simpler than it sounds.
"""

from __future__ import annotations

import os
from pathlib import Path

from control_plane import paths


def _route_file(route_id: str) -> Path:
    return paths.dynamic_dir() / f"route-{route_id}.yml"


def write_route(
    route_id: str,
    subdomain: str,
    target_ip: str,
    target_port: int,
    cert_resolver: str | None,
) -> None:
    """(Re)write the dynamic-config file that makes `subdomain` proxy to
    `target_ip:target_port`. Idempotent — safe to call for an unchanged
    route, which is what reconciler.py relies on.
    """
    if cert_resolver:
        tls_block = f"      tls:\n        certResolver: {cert_resolver}\n"
    else:
        tls_block = "      tls: {}\n"

    content = (
        "http:\n"
        "  routers:\n"
        f"    route-{route_id}:\n"
        f'      rule: "Host(`{subdomain}`)"\n'
        "      entryPoints: [websecure]\n"
        f"      service: svc-{route_id}\n"
        f"{tls_block}"
        "  services:\n"
        f"    svc-{route_id}:\n"
        "      loadBalancer:\n"
        "        servers:\n"
        f'          - url: "http://{target_ip}:{target_port}"\n'
    )

    target = _route_file(route_id)
    target.parent.mkdir(parents=True, exist_ok=True)
    tmp = target.with_suffix(".tmp")
    tmp.write_text(content)
    os.replace(tmp, target)


def remove_route(route_id: str) -> None:
    _route_file(route_id).unlink(missing_ok=True)


def existing_route_ids() -> set[str]:
    return {
        f.name.removeprefix("route-").removesuffix(".yml")
        for f in paths.dynamic_dir().glob("route-*.yml")
    }