"""Application configuration loaded from env, .env, and TOML file via pydantic-settings."""

from __future__ import annotations

from pathlib import Path
from typing import Literal

from platformdirs import PlatformDirs
from pydantic import Field, ValidationError, field_validator
from pydantic_settings import (
    BaseSettings,
    PydanticBaseSettingsSource,
    SettingsConfigDict,
    TomlConfigSettingsSource,
)

from .enums import ErrorClass
from .errors import MyDeepAgentError

_DIRS = PlatformDirs("my-deepagent", "user", roaming=False)


class Config(BaseSettings):
    """Frozen application config. Source priority (high -> low): CLI/env, .env, TOML, defaults."""

    model_config = SettingsConfigDict(
        env_prefix="MYDEEPAGENT_",
        env_file=".env",
        env_file_encoding="utf-8",
        toml_file=Path(_DIRS.user_config_dir) / "config.toml",
        frozen=True,
        extra="ignore",
    )

    # storage
    database_url: str = Field(
        default_factory=lambda: (
            f"sqlite+aiosqlite:///{Path(_DIRS.user_data_dir) / 'database.sqlite3'}"
        )
    )
    workspace_root: Path = Field(default_factory=Path.cwd)
    data_dir: Path = Field(default_factory=lambda: Path(_DIRS.user_data_dir))
    config_dir: Path = Field(default_factory=lambda: Path(_DIRS.user_config_dir))
    state_dir: Path = Field(default_factory=lambda: Path(_DIRS.user_state_dir))

    # logging / i18n
    log_level: Literal["trace", "debug", "info", "warn", "error"] = "info"
    lang: Literal["ko", "en"] = "ko"

    # providers
    openrouter_api_key: str | None = None
    openrouter_base_url: str = "https://openrouter.ai/api/v1"

    # observability
    langsmith_tracing: bool = False
    langsmith_api_key: str | None = None
    langsmith_project: str = "my-deepagent"

    # budget
    budget_daily_usd: float = Field(default=5.0, ge=0)
    budget_daily_warn_usd: float = Field(default=3.0, ge=0)
    budget_run_usd: float = Field(default=1.0, ge=0)
    budget_run_warn_usd: float = Field(default=0.5, ge=0)
    budget_on_hit: Literal["prompt", "block", "warn_continue"] = "prompt"

    # defaults
    default_persona: str = "default-interactive"

    @field_validator("workspace_root", "data_dir", "config_dir", "state_dir")
    @classmethod
    def _expand(cls, v: Path) -> Path:
        return Path(v).expanduser().resolve()

    @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, ...]:
        # priority: init > env > dotenv > toml > defaults
        return (
            init_settings,
            env_settings,
            dotenv_settings,
            TomlConfigSettingsSource(settings_cls),
            file_secret_settings,
        )


def load_config(**overrides: object) -> Config:
    """Load Config with optional kwargs override.

    Wraps pydantic ValidationError in MyDeepAgentError(fatal, config_invalid) per plan §18.
    """
    try:
        return Config(**overrides)  # type: ignore[arg-type]
    except ValidationError as e:
        raise MyDeepAgentError(
            ErrorClass.FATAL,
            "config_invalid",
            message=f"config validation failed: {e}",
            recovery_hint=(
                "check .env, environment variables, and ~/.config/my-deepagent/config.toml"
            ),
            cause=e,
        ) from e