from __future__ import annotations

import dataclasses
from typing import List, Optional

import yaml


class ConfigError(Exception):
    """Raised for any problem with the config file's contents."""


@dataclasses.dataclass
class Endpoint:
    name: str
    host: str
    scheme: str  # "http" or "https"
    port: int
    dns_server: str  # DNS server used to resolve `host` — the system/router
    # resolver is never consulted, see app/dns_resolver.py
    expected_status: int
    path: str = "/"
    timeout_seconds: Optional[float] = None
    verify_tls: bool = True  # set False for endpoints with self-signed certs


@dataclasses.dataclass
class InfluxConfig:
    url: str
    token: str
    org: str
    bucket: str
    verify_ssl: bool = False  # default off: influx uses a self-signed cert


@dataclasses.dataclass
class CheckConfig:
    interval_seconds: int = 600
    timeout_seconds: float = 10.0
    immediate_recheck_delay_seconds: float = 5.0


@dataclasses.dataclass
class AppConfig:
    influx: InfluxConfig
    check: CheckConfig
    endpoints: List[Endpoint]


def _require(d: dict, key: str, ctx: str):
    value = d.get(key)
    if value in (None, ""):
        raise ConfigError(f"Missing required field '{key}' in {ctx}")
    return value


def load_config(path: str) -> AppConfig:
    try:
        with open(path, "r", encoding="utf-8") as f:
            raw = yaml.safe_load(f)
    except FileNotFoundError:
        raise ConfigError(f"Config file not found: {path}")
    except yaml.YAMLError as e:
        raise ConfigError(f"Invalid YAML in config file '{path}': {e}")

    if not raw:
        raise ConfigError(f"Config file '{path}' is empty")

    influx_raw = raw.get("influx") or {}
    influx = InfluxConfig(
        url=_require(influx_raw, "url", "influx"),
        token=_require(influx_raw, "token", "influx"),
        org=_require(influx_raw, "org", "influx"),
        bucket=_require(influx_raw, "bucket", "influx"),
        verify_ssl=bool(influx_raw.get("verify_ssl", False)),
    )

    check_raw = raw.get("check") or {}
    check = CheckConfig(
        interval_seconds=int(check_raw.get("interval_seconds", 600)),
        timeout_seconds=float(check_raw.get("timeout_seconds", 10.0)),
        immediate_recheck_delay_seconds=float(
            check_raw.get("immediate_recheck_delay_seconds", 5.0)
        ),
    )

    endpoints_raw = raw.get("endpoints") or []
    if not endpoints_raw:
        raise ConfigError("No endpoints configured under 'endpoints'")

    endpoints: List[Endpoint] = []
    seen_names = set()
    for i, ep in enumerate(endpoints_raw):
        ctx = f"endpoints[{i}]"
        name = _require(ep, "name", ctx)
        if name in seen_names:
            raise ConfigError(f"Duplicate endpoint name: '{name}'")
        seen_names.add(name)

        scheme = str(_require(ep, "scheme", ctx)).lower()
        if scheme not in ("http", "https"):
            raise ConfigError(
                f"{ctx} ('{name}'): scheme must be 'http' or 'https', got '{scheme}'"
            )

        timeout = ep.get("timeout_seconds")
        endpoints.append(
            Endpoint(
                name=name,
                host=_require(ep, "host", ctx),
                scheme=scheme,
                port=int(_require(ep, "port", ctx)),
                dns_server=_require(ep, "dns_server", ctx),
                expected_status=int(_require(ep, "expected_status", ctx)),
                path=ep.get("path", "/"),
                timeout_seconds=float(timeout) if timeout else None,
                verify_tls=bool(ep.get("verify_tls", True)),
            )
        )

    return AppConfig(influx=influx, check=check, endpoints=endpoints)