"""Environment-backed application configuration."""

from decimal import Decimal
from functools import lru_cache
from pathlib import Path
from typing import Literal

from pydantic import Field
from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    """Validated process configuration at the application boundary."""

    app_name: str = "Zhixing Server"
    app_env: Literal["development", "test", "production"] = "development"
    log_level: str = "INFO"
    database_url: str = "postgresql://zhixing:zhixing@localhost:5432/zhixing"
    tushare_token: str = ""
    market_data_csv_root: Path = Path("./data/market-data")
    market_data_coverage_threshold: Decimal = Decimal("0.99")
    market_data_max_workers: int = Field(default=8, ge=1)
    market_data_request_interval_seconds: float = 0.2
    market_data_max_retries: int = 3
    market_data_retry_backoff_seconds: float = 1.0
    market_data_advisory_lock_key: int = 7_380_521
    sector_radar_coverage_threshold: Decimal = Decimal("0.99")
    sector_radar_request_interval_seconds: float = 0.2
    sector_radar_max_retries: int = 3
    sector_radar_retry_backoff_seconds: float = 1.0
    sector_radar_advisory_lock_key: int = 7_380_522
    selection_max_workers: int = Field(default=4, ge=1)
    selection_batch_size: int = Field(default=200, ge=1)
    selection_pattern_scoring_enabled: bool = True

    model_config = SettingsConfigDict(
        env_file=".env",
        env_prefix="ZHIXING_",
        extra="ignore",
    )


def sqlalchemy_database_url(database_url: str) -> str:
    """Add SQLAlchemy's Psycopg 3 driver to a PostgreSQL URL.

    ``Settings.database_url`` remains a plain ``postgresql://`` URL because
    Psycopg 3 accepts that form directly.  Alembic and SQLAlchemy need the
    explicit ``postgresql+psycopg://`` dialect, while the rest of the URL
    (including query parameters such as ``sslmode``) must remain unchanged.

    Args:
        database_url: PostgreSQL connection URL from the process environment.

    Returns:
        The URL with SQLAlchemy's Psycopg 3 dialect prefix.

    Raises:
        ValueError: If the URL does not use a supported PostgreSQL scheme.
    """

    if database_url.startswith("postgresql+psycopg://"):
        return database_url
    if database_url.startswith("postgresql://"):
        return "postgresql+psycopg://" + database_url.removeprefix("postgresql://")
    raise ValueError("database_url must use postgresql:// or postgresql+psycopg://")


@lru_cache
def get_settings() -> Settings:
    """Return one immutable-by-convention configuration object per process.

    Returns:
        Settings populated from defaults, `.env`, and process environment variables.
    """
    return Settings()