"""Application settings loaded from TOML with env-var overrides."""

from __future__ import annotations

import os
from pathlib import Path

from pydantic import BaseModel, Field
from pydantic_settings import (
    BaseSettings,
    PydanticBaseSettingsSource,
    SettingsConfigDict,
    TomlConfigSettingsSource,
)


class MeshCoreCfg(BaseModel):
    serial_port: str
    baud_rate: int = 115200


class LLMCfg(BaseModel):
    base_url: str
    api_key: str = "not-needed"
    model: str
    system_prompt: str = (
        "You are a concise assistant on a low-bandwidth mesh radio. "
        "Replies must be brief — under 180 bytes."
    )
    temperature: float = 0.7
    request_timeout_seconds: float = 60.0


class StorageCfg(BaseModel):
    sqlite_path: Path = Path("data/meshbot.db")


class MessageCfg(BaseModel):
    max_bytes: int = Field(default=184, gt=0)


def _toml_path() -> Path:
    return Path(os.environ.get("MESHBOT_CONFIG", "config.toml"))


class Settings(BaseSettings):
    meshcore: MeshCoreCfg
    llm: LLMCfg
    storage: StorageCfg = StorageCfg()
    message: MessageCfg = MessageCfg()

    model_config = SettingsConfigDict(
        env_prefix="MESHBOT_",
        env_nested_delimiter="__",
        toml_file=_toml_path(),
        extra="ignore",
    )

    @classmethod
    def settings_customise_sources(
        cls,
        settings_cls: type[BaseSettings],
        init_settings: PydanticBaseSettingsSource,
        env_settings: PydanticBaseSettingsSource,
        dotenv_settings: PydanticBaseSettingsSource,
        file_secret_settings: PydanticBaseSettingsSource,
    ) -> tuple[PydanticBaseSettingsSource, ...]:
        # Order = priority (highest first): init args > env > TOML > secrets.
        return (
            init_settings,
            env_settings,
            TomlConfigSettingsSource(settings_cls),
            file_secret_settings,
        )