"""Configuration loading, validation, and persistence for HAMeter.

All configuration is managed through the web UI and stored as JSON
at /data/config.json. A YAML config file can be imported as a
one-time migration.
"""

import json
import logging
import os
import tempfile
from dataclasses import dataclass, field
from typing import Optional

import yaml

logger = logging.getLogger(__name__)

VALID_PROTOCOLS = {"scm", "scm+", "idm", "netidm", "r900", "r900bcd"}
VALID_RATE_TYPES = {"per_unit", "fixed"}

# Default icons/unit per common meter type.
_METER_DEFAULTS = {
    "energy": {"icon": "mdi:flash", "unit": "kWh"},
    "gas": {"icon": "mdi:fire", "unit": "ft\u00b3"},
    "water": {"icon": "mdi:water", "unit": "gal"},
}

CONFIG_PATH = "/data/config.json"


# ------------------------------------------------------------------ #
# Dataclasses
# ------------------------------------------------------------------ #

@dataclass
class MqttConfig:
    host: str
    port: int = 1883
    user: str = ""
    password: str = ""
    base_topic: str = "hameter"
    ha_autodiscovery: bool = True
    ha_autodiscovery_topic: str = "homeassistant"
    client_id: str = "hameter"


@dataclass
class RateComponent:
    name: str
    rate: float
    type: str = "per_unit"


@dataclass
class MeterConfig:
    id: int
    protocol: str
    name: str
    unit_of_measurement: str
    icon: str = "mdi:gauge"
    device_class: str = ""
    state_class: str = "total_increasing"
    multiplier: float = 1.0
    cost_factors: list[RateComponent] = field(default_factory=list)


@dataclass
class GeneralConfig:
    sleep_for: int = 0
    device_id: str = "0"
    rtl_tcp_host: str = "127.0.0.1"
    rtl_tcp_port: int = 1234
    log_level: str = "INFO"
    rtlamr_extra_args: list = field(default_factory=list)


@dataclass
class HaMeterConfig:
    general: GeneralConfig
    mqtt: MqttConfig
    meters: list[MeterConfig]


# ------------------------------------------------------------------ #
# Config file operations
# ------------------------------------------------------------------ #

def config_exists(path: Optional[str] = None) -> bool:
    """Check if a config file exists at the standard path."""
    return os.path.isfile(path or CONFIG_PATH)


def load_config_from_json(path: Optional[str] = None) -> HaMeterConfig:
    """Load configuration from a JSON file.

    Raises:
        FileNotFoundError: If config file does not exist.
        ValueError: For validation errors.
    """
    path = path or CONFIG_PATH
    with open(path) as f:
        raw = json.load(f)

    if not isinstance(raw, dict):
        raise ValueError(f"Config file is not a valid JSON object: {path}")

    return _build_config_from_dict(raw)


def load_config_from_yaml(path: str) -> HaMeterConfig:
    """Load from YAML file (migration path from older versions).

    Raises:
        FileNotFoundError: If YAML file does not exist.
        ValueError: For validation errors.
    """
    with open(path) as f:
        raw = yaml.safe_load(f) or {}

    if not isinstance(raw, dict):
        raise ValueError(f"YAML file is not a valid mapping: {path}")

    return _build_config_from_dict(raw)


def save_config(config: HaMeterConfig, path: Optional[str] = None):
    """Atomically write config to JSON file.

    Writes to a temp file in the same directory, then os.replace()
    for atomic rename. This prevents corruption on power loss.
    """
    path = path or CONFIG_PATH
    data = config_to_dict(config)

    dir_path = os.path.dirname(path)
    if dir_path:
        os.makedirs(dir_path, exist_ok=True)

    fd, tmp_path = tempfile.mkstemp(dir=dir_path or ".", suffix=".tmp")
    try:
        with os.fdopen(fd, "w") as f:
            json.dump(data, f, indent=2)
            f.write("\n")
            f.flush()
            os.fsync(f.fileno())
        os.replace(tmp_path, path)
    except Exception:
        try:
            os.unlink(tmp_path)
        except OSError:
            pass
        raise


def config_to_dict(config: HaMeterConfig) -> dict:
    """Serialize HaMeterConfig to a JSON-safe dict."""
    return {
        "general": {
            "sleep_for": config.general.sleep_for,
            "device_id": config.general.device_id,
            "rtl_tcp_host": config.general.rtl_tcp_host,
            "rtl_tcp_port": config.general.rtl_tcp_port,
            "log_level": config.general.log_level,
            "rtlamr_extra_args": config.general.rtlamr_extra_args,
        },
        "mqtt": {
            "host": config.mqtt.host,
            "port": config.mqtt.port,
            "user": config.mqtt.user,
            "password": config.mqtt.password,
            "base_topic": config.mqtt.base_topic,
            "ha_autodiscovery": config.mqtt.ha_autodiscovery,
            "ha_autodiscovery_topic": config.mqtt.ha_autodiscovery_topic,
            "client_id": config.mqtt.client_id,
        },
        "meters": [
            {
                "id": m.id,
                "protocol": m.protocol,
                "name": m.name,
                "unit_of_measurement": m.unit_of_measurement,
                "icon": m.icon,
                "device_class": m.device_class,
                "state_class": m.state_class,
                "multiplier": m.multiplier,
                "cost_factors": [
                    {"name": cf.name, "rate": cf.rate, "type": cf.type}
                    for cf in m.cost_factors
                ],
            }
            for m in config.meters
        ],
    }


# ------------------------------------------------------------------ #
# Validation helpers
# ------------------------------------------------------------------ #

def validate_mqtt_config(data: dict) -> tuple[bool, str]:
    """Validate MQTT config fields, return (ok, error_message)."""
    if not data.get("host", "").strip():
        return False, "MQTT host is required"
    port = data.get("port", 1883)
    try:
        port = int(port)
        if not (1 <= port <= 65535):
            raise ValueError
    except (ValueError, TypeError):
        return False, f"Invalid port: {port}"
    return True, ""


def validate_meter_config(data: dict) -> tuple[bool, str]:
    """Validate a single meter config dict, return (ok, error_message)."""
    if not data.get("id"):
        return False, "Meter ID is required"
    try:
        int(data["id"])
    except (ValueError, TypeError):
        return False, f"Meter ID must be a number: {data['id']}"

    protocol = data.get("protocol", "").lower()
    if protocol not in VALID_PROTOCOLS:
        return False, (
            f"Invalid protocol: {protocol}. "
            f"Valid: {', '.join(sorted(VALID_PROTOCOLS))}"
        )

    if not data.get("name", "").strip():
        return False, "Meter name is required"

    multiplier = data.get("multiplier", 1.0)
    try:
        multiplier = float(multiplier)
    except (ValueError, TypeError):
        return False, f"Multiplier must be a number: {data.get('multiplier')}"
    if multiplier <= 0:
        return False, f"Multiplier must be positive, got {multiplier}"

    return True, ""


def validate_rate_component(data: dict) -> tuple[bool, str]:
    """Validate a single rate component dict, return (ok, error_message)."""
    if not data.get("name", "").strip():
        return False, "Rate component name is required"
    try:
        float(data.get("rate", ""))
    except (ValueError, TypeError):
        return False, f"Rate must be a number: {data.get('rate')}"
    comp_type = data.get("type", "per_unit")
    if comp_type not in VALID_RATE_TYPES:
        return False, f"Invalid rate type: {comp_type}. Must be 'per_unit' or 'fixed'"
    return True, ""


def get_meter_defaults(device_class: str) -> dict:
    """Get smart defaults (icon, unit) for a device class."""
    return dict(_METER_DEFAULTS.get(device_class, {}))


# ------------------------------------------------------------------ #
# Internal builders
# ------------------------------------------------------------------ #

def _build_config_from_dict(raw: dict) -> HaMeterConfig:
    """Build HaMeterConfig from a raw dict (from JSON or YAML)."""
    general = _build_general_from_dict(raw)
    mqtt = _build_mqtt_from_dict(raw)
    meters = _build_meters_from_dict(raw)
    return HaMeterConfig(general=general, mqtt=mqtt, meters=meters)


def _build_general_from_dict(raw: dict) -> GeneralConfig:
    """Build GeneralConfig from raw dict."""
    g = raw.get("general", {})
    extra_args = g.get("rtlamr_extra_args", [])
    if isinstance(extra_args, str):
        extra_args = extra_args.split()

    rtl_tcp_port = int(g.get("rtl_tcp_port", 1234))
    if not (1 <= rtl_tcp_port <= 65535):
        raise ValueError(
            f"rtl_tcp_port must be 1-65535, got {rtl_tcp_port}"
        )

    log_level = str(g.get("log_level", "INFO")).upper()
    if log_level not in ("DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"):
        raise ValueError(
            f"Invalid log_level '{log_level}'. "
            f"Valid: DEBUG, INFO, WARNING, ERROR, CRITICAL"
        )

    device_id = str(g.get("device_id", "0"))
    try:
        if int(device_id) < 0:
            raise ValueError
    except (ValueError, TypeError):
        raise ValueError(
            f"device_id must be a non-negative integer, got '{device_id}'"
        )

    return GeneralConfig(
        sleep_for=int(g.get("sleep_for", 0)),
        device_id=device_id,
        rtl_tcp_host=g.get("rtl_tcp_host", "127.0.0.1"),
        rtl_tcp_port=rtl_tcp_port,
        log_level=log_level,
        rtlamr_extra_args=list(extra_args),
    )


def _build_mqtt_from_dict(raw: dict) -> MqttConfig:
    """Build MqttConfig from raw dict."""
    m = raw.get("mqtt") or {}

    host = m.get("host", "")
    if not host:
        raise ValueError(
            "MQTT host not set. Configure it via the web UI."
        )

    port = int(m.get("port", 1883))
    if not (1 <= port <= 65535):
        raise ValueError(f"MQTT port must be 1-65535, got {port}")

    return MqttConfig(
        host=host,
        port=port,
        user=m.get("user", ""),
        password=m.get("password", ""),
        base_topic=m.get("base_topic", "hameter"),
        ha_autodiscovery=m.get("ha_autodiscovery", True),
        ha_autodiscovery_topic=m.get("ha_autodiscovery_topic", "homeassistant"),
        client_id=m.get("client_id", "hameter"),
    )


def _build_meters_from_dict(raw: dict) -> list[MeterConfig]:
    """Build meter list from raw dict."""
    meters_raw = raw.get("meters")
    if not meters_raw:
        return []

    meters = []
    seen_ids: set[int] = set()
    for i, m in enumerate(meters_raw):
        meter_id = m.get("id")
        if meter_id is None:
            raise ValueError(f"Meter #{i + 1} missing required 'id'")

        mid_int = int(meter_id)
        if mid_int in seen_ids:
            raise ValueError(
                f"Meter #{i + 1} has duplicate id {mid_int}"
            )
        seen_ids.add(mid_int)

        protocol = m.get("protocol", "").lower()
        if protocol not in VALID_PROTOCOLS:
            raise ValueError(
                f"Meter #{i + 1} (id={meter_id}) has invalid protocol "
                f"'{protocol}'. Valid: {', '.join(sorted(VALID_PROTOCOLS))}"
            )

        name = m.get("name", "")
        if not name:
            raise ValueError(
                f"Meter #{i + 1} (id={meter_id}) missing required 'name'"
            )

        # Apply smart defaults based on device_class.
        device_class = m.get("device_class", "")
        defaults = _METER_DEFAULTS.get(device_class, {})

        cost_factors = [
            RateComponent(
                name=cf.get("name", ""),
                rate=float(cf.get("rate", 0.0)),
                type=cf.get("type", "per_unit"),
            )
            for cf in m.get("cost_factors", [])
        ]

        meters.append(MeterConfig(
            id=int(meter_id),
            protocol=protocol,
            name=name,
            unit_of_measurement=m.get("unit_of_measurement", "") or defaults.get("unit", ""),
            icon=m.get("icon", "") or defaults.get("icon", "mdi:gauge"),
            device_class=device_class,
            state_class=m.get("state_class", "total_increasing"),
            multiplier=float(m.get("multiplier", 1.0)),
            cost_factors=cost_factors,
        ))

    return meters