"""Configuration loading from TOML with environment variable overrides."""

from __future__ import annotations

import os
import tomllib
from dataclasses import dataclass, field
from pathlib import Path


@dataclass
class ServerConfig:
    """[server] section."""

    socket_path: str = "/run/nix-builder-autoscaler/daemon.sock"
    log_level: str = "info"
    db_path: str = "/var/lib/nix-builder-autoscaler/state.db"


@dataclass
class AwsConfig:
    """[aws] section."""

    region: str = "us-east-1"
    launch_template_id: str = ""
    subnet_ids: list[str] = field(default_factory=list)
    security_group_ids: list[str] = field(default_factory=list)
    instance_profile_arn: str = ""


@dataclass
class HaproxyConfig:
    """[haproxy] section."""

    runtime_socket: str = "/run/haproxy/admin.sock"
    backend: str = "all"
    slot_prefix: str = "slot"
    slot_count: int = 8
    check_ready_up_count: int = 2


@dataclass
class SystemConfig:
    """[[systems]] entry for per-architecture capacity policy."""

    name: str = "x86_64-linux"
    min_slots: int = 0
    max_slots: int = 8
    target_warm_slots: int = 0
    max_leases_per_slot: int = 1
    launch_batch_size: int = 1
    scale_down_idle_seconds: int = 900


@dataclass
class CapacityConfig:
    """[capacity] section — global defaults."""

    default_system: str = "x86_64-linux"
    min_slots: int = 0
    max_slots: int = 8
    target_warm_slots: int = 0
    max_leases_per_slot: int = 1
    reservation_ttl_seconds: int = 1200
    idle_scale_down_seconds: int = 900
    drain_timeout_seconds: int = 120
    launch_timeout_seconds: int = 300
    boot_timeout_seconds: int = 300
    binding_timeout_seconds: int = 180
    terminating_timeout_seconds: int = 300


@dataclass
class SecurityConfig:
    """[security] section."""

    socket_mode: str = "0660"
    socket_owner: str = "buildbot"
    socket_group: str = "buildbot"


@dataclass
class SchedulerConfig:
    """[scheduler] section."""

    tick_seconds: float = 3.0
    reconcile_seconds: float = 15.0


@dataclass
class AppConfig:
    """Top-level application configuration."""

    server: ServerConfig = field(default_factory=ServerConfig)
    aws: AwsConfig = field(default_factory=AwsConfig)
    haproxy: HaproxyConfig = field(default_factory=HaproxyConfig)
    capacity: CapacityConfig = field(default_factory=CapacityConfig)
    security: SecurityConfig = field(default_factory=SecurityConfig)
    scheduler: SchedulerConfig = field(default_factory=SchedulerConfig)
    systems: list[SystemConfig] = field(default_factory=list)


# ---------------------------------------------------------------------------
# Environment variable overrides
# ---------------------------------------------------------------------------
# AUTOSCALER_TAILSCALE_API_TOKEN — Tailscale API token for IP discovery
# AWS_REGION                     — override aws.region
# AWS_ACCESS_KEY_ID              — explicit AWS credential
# AWS_SECRET_ACCESS_KEY          — explicit AWS credential


def _apply_env_overrides(cfg: AppConfig) -> None:
    """Apply environment variable overrides for secrets and region."""
    region = os.environ.get("AWS_REGION")
    if region:
        cfg.aws.region = region


def _build_dataclass(cls: type, data: dict) -> object:  # noqa: ANN001
    """Construct a dataclass from a dict, ignoring unknown keys."""
    valid = {f.name for f in cls.__dataclass_fields__.values()}  # type: ignore[attr-defined]
    return cls(**{k: v for k, v in data.items() if k in valid})


def load_config(path: Path) -> AppConfig:
    """Load configuration from a TOML file.

    Args:
        path: Path to the TOML config file.

    Returns:
        Validated AppConfig instance.
    """
    with open(path, "rb") as f:
        raw = tomllib.load(f)

    cfg = AppConfig()

    if "server" in raw:
        cfg.server = _build_dataclass(ServerConfig, raw["server"])  # type: ignore[assignment]
    if "aws" in raw:
        cfg.aws = _build_dataclass(AwsConfig, raw["aws"])  # type: ignore[assignment]
    if "haproxy" in raw:
        cfg.haproxy = _build_dataclass(HaproxyConfig, raw["haproxy"])  # type: ignore[assignment]
    if "capacity" in raw:
        cfg.capacity = _build_dataclass(CapacityConfig, raw["capacity"])  # type: ignore[assignment]
    if "security" in raw:
        cfg.security = _build_dataclass(SecurityConfig, raw["security"])  # type: ignore[assignment]
    if "scheduler" in raw:
        cfg.scheduler = _build_dataclass(SchedulerConfig, raw["scheduler"])  # type: ignore[assignment]

    if "systems" in raw:
        cfg.systems = list[SystemConfig](
            _build_dataclass(SystemConfig, s)  # type: ignore[list-item]
            for s in raw["systems"]
        )

    _apply_env_overrides(cfg)
    return cfg