"""YAML config loading and validation.

Config file path: ~/.config/mcp-synology-filestation/config.yaml

Loading order:
1. Parse YAML file
2. Merge environment variable overrides
3. Validate with dataclasses
"""

from __future__ import annotations

import logging
import os
from dataclasses import dataclass
from pathlib import Path
from typing import Any

import yaml

logger = logging.getLogger(__name__)

CONFIG_DIR = Path.home() / ".config" / "mcp-synology-filestation"
CONFIG_PATH = CONFIG_DIR / "config.yaml"
CURRENT_SCHEMA_VERSION = 1

# Environment variable overrides (env var -> config key path)
ENV_VAR_MAP: dict[str, str] = {
    "SYNOLOGY_HOST": "connection.host",
    "SYNOLOGY_PORT": "connection.port",
    "SYNOLOGY_HTTPS": "connection.https",
    "SYNOLOGY_VERIFY_SSL": "connection.verify_ssl",
    "SYNOLOGY_USERNAME": "auth.username",
    "SYNOLOGY_PASSWORD": "auth.password",
}


@dataclass
class ConnectionConfig:
    """NAS connection settings."""

    host: str
    port: int = 443
    https: bool = True
    verify_ssl: bool = True
    timeout: int = 30


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

    schema_version: int
    connection: ConnectionConfig
    alias: str | None = None

    @property
    def base_url(self) -> str:
        """Build base URL for DSM API calls."""
        scheme = "https" if self.connection.https else "http"
        return f"{scheme}://{self.connection.host}:{self.connection.port}"

    @property
    def keyring_service(self) -> str:
        """Keyring service name."""
        return "mcp-synology-filestation"


def _merge_env_overrides(raw: dict[str, Any]) -> dict[str, Any]:
    """Merge environment variable overrides into raw config dict."""
    for env_var, dotted_path in ENV_VAR_MAP.items():
        value = os.environ.get(env_var)
        if value is None:
            continue

        logger.debug("Env override: %s -> %s", env_var, dotted_path)
        parts = dotted_path.split(".")
        target = raw
        for part in parts[:-1]:
            if part not in target or not isinstance(target[part], dict):
                target[part] = {}
            target = target[part]

        key = parts[-1]
        # Type coercion for known non-string values
        if key == "port" or key == "timeout":
            target[key] = int(value)
        elif key in ("https", "verify_ssl"):
            target[key] = value.lower() in ("true", "1", "yes")
        else:
            target[key] = value

    return raw


def load_config(path: str | Path | None = None) -> AppConfig:
    """Load, validate, and return the application config.

    Args:
        path: Explicit config file path, or None to use default location.

    Raises:
        FileNotFoundError: If config file does not exist.
        ValueError: If config is invalid.
    """
    config_path = Path(path) if path else CONFIG_PATH

    if not config_path.exists():
        msg = (
            f"Config file not found: {config_path}\n"
            "Run 'mcp-synology-filestation setup' to create it."
        )
        raise FileNotFoundError(msg)

    logger.debug("Loading config from %s", config_path)
    raw_text = config_path.read_text(encoding="utf-8")
    raw: dict[str, Any] = yaml.safe_load(raw_text) or {}

    raw = _merge_env_overrides(raw)

    return _validate_config(raw)


def _validate_config(raw: dict[str, Any]) -> AppConfig:
    """Validate raw config dict and return AppConfig.

    Args:
        raw: Raw config dictionary from YAML.

    Raises:
        ValueError: If required fields are missing or invalid.
    """
    schema_version = raw.get("schema_version")
    if schema_version != CURRENT_SCHEMA_VERSION:
        msg = f"Config schema_version is {schema_version!r}, expected {CURRENT_SCHEMA_VERSION}."
        raise ValueError(msg)

    conn_raw = raw.get("connection", {})
    if not conn_raw.get("host"):
        msg = (
            "connection.host is required. "
            "Set it in the config file or via SYNOLOGY_HOST environment variable."
        )
        raise ValueError(msg)

    connection = ConnectionConfig(
        host=conn_raw["host"],
        port=int(conn_raw.get("port", 443)),
        https=bool(conn_raw.get("https", True)),
        verify_ssl=bool(conn_raw.get("verify_ssl", True)),
        timeout=int(conn_raw.get("timeout", 30)),
    )

    return AppConfig(
        schema_version=schema_version,
        connection=connection,
        alias=raw.get("alias"),
    )


def save_config(config: AppConfig, path: str | Path | None = None) -> None:
    """Save AppConfig to YAML file.

    Args:
        config: AppConfig instance to save.
        path: Target file path, or None to use default location.
    """
    config_path = Path(path) if path else CONFIG_PATH
    config_path.parent.mkdir(parents=True, exist_ok=True)

    data: dict[str, Any] = {
        "schema_version": config.schema_version,
        "connection": {
            "host": config.connection.host,
            "port": config.connection.port,
            "https": config.connection.https,
            "verify_ssl": config.connection.verify_ssl,
            "timeout": config.connection.timeout,
        },
    }
    if config.alias:
        data["alias"] = config.alias

    header = "# Generated by mcp-synology-filestation setup\n"
    config_path.write_text(
        header + yaml.dump(data, default_flow_style=False, sort_keys=False),
        encoding="utf-8",
    )
    logger.debug("Config saved to %s", config_path)