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

from app.db.models import Base

# Columns added to existing tables after their initial release. create_all()
# only creates missing tables, never adds columns to tables that already
# exist, so a column added to a model here must also be listed below or an
# already-deployed database will never receive it and the app will crash
# reading/writing that column.
_ADDITIVE_COLUMNS: dict[str, list[tuple[str, str]]] = {
    "sync_users": [
        ("notify_email_enabled", "BOOLEAN NOT NULL DEFAULT 0"),
        ("notification_email", "VARCHAR(255)"),
    ],
}


def create_db_engine(database_url: str) -> Engine:
    connect_args = {"check_same_thread": False} if database_url.startswith("sqlite") else {}
    return create_engine(database_url, connect_args=connect_args, future=True)


def create_session_factory(engine: Engine) -> sessionmaker[Session]:
    return sessionmaker(bind=engine, autoflush=False, expire_on_commit=False)


def initialize_schema(engine: Engine) -> None:
    Base.metadata.create_all(engine)
    _apply_additive_migrations(engine)


def _apply_additive_migrations(engine: Engine) -> None:
    if engine.dialect.name != "sqlite":
        # ALTER TABLE ... ADD COLUMN syntax/type names below are only
        # verified against sqlite, the only backend this app is deployed
        # against; a fresh create_all() on another backend already has every
        # current column, so skipping here only matters for a pre-existing
        # non-sqlite database, which does not exist in practice.
        return
    inspector = inspect(engine)
    existing_tables = set(inspector.get_table_names())
    with engine.begin() as conn:
        for table, columns in _ADDITIVE_COLUMNS.items():
            if table not in existing_tables:
                continue
            existing_columns = {col["name"] for col in inspector.get_columns(table)}
            for name, ddl_type in columns:
                if name not in existing_columns:
                    conn.execute(text(f"ALTER TABLE {table} ADD COLUMN {name} {ddl_type}"))