from __future__ import annotations

import logging
from collections.abc import Iterator

from sqlalchemy import Engine, create_engine, inspect, text
from sqlalchemy.orm import Session, sessionmaker

from app.config import REPO_ROOT, get_settings
from app.models import Base

logger = logging.getLogger(__name__)

_settings = get_settings()

# Additive migrations for existing databases. ``create_all`` only creates missing
# tables; it never alters existing ones, so new nullable/defaulted columns are
# added here as (table, column, DDL type) tuples.
_ADDITIVE_COLUMNS: list[tuple[str, str, str]] = [
    ("strategy_configs", "name", "VARCHAR(80) DEFAULT ''"),
]


def _normalize_url(url: str) -> tuple[str, dict]:
    connect_args: dict = {}
    if url.startswith("sqlite"):
        prefix, _, path = url.partition("sqlite:///")
        if path and not path.startswith("/"):
            url = f"{prefix}sqlite:///{REPO_ROOT / path}"
        connect_args = {"check_same_thread": False}
    return url, connect_args


_url, _connect_args = _normalize_url(_settings.database_url)
engine = create_engine(_url, connect_args=_connect_args, pool_pre_ping=True)
SessionLocal = sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)


def _apply_additive_columns(target: Engine) -> None:
    inspector = inspect(target)
    existing_tables = set(inspector.get_table_names())
    with target.begin() as connection:
        for table, column, ddl in _ADDITIVE_COLUMNS:
            if table not in existing_tables:
                continue
            columns = {col["name"] for col in inspector.get_columns(table)}
            if column in columns:
                continue
            logger.info("migrating: adding %s.%s", table, column)
            connection.execute(text(f"ALTER TABLE {table} ADD COLUMN {column} {ddl}"))


def init_db() -> None:
    Base.metadata.create_all(bind=engine)
    _apply_additive_columns(engine)


def get_session() -> Iterator[Session]:
    session = SessionLocal()
    try:
        yield session
    finally:
        session.close()