"""Alembic migration environment.

Wired to:
* ``app.db.base.Base.metadata`` (the single source of truth for our schema), and
* ``app.config.get_settings().db_url`` (the same URL the application uses).

Production runs against MySQL via ``mysql+asyncmy://``. Alembic drives a
**synchronous** engine, so :func:`_sync_url` swaps the async driver for its
sync counterpart (``mysql+asyncmy`` -> ``mysql+pymysql`` and
``sqlite+aiosqlite`` -> ``sqlite``). For local autogenerate without a running
MySQL server, point ``DB_URL`` at an empty SQLite file, e.g.::

    DB_URL="sqlite+aiosqlite:///./_autogen.db" alembic revision --autogenerate -m "..."
"""

from logging.config import fileConfig

from alembic import context
from sqlalchemy import engine_from_config, pool

from app.config import get_settings
from app.db import models  # noqa: F401  (registers all tables on Base.metadata)
from app.db.base import Base

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
if config.config_file_name is not None:
    fileConfig(config.config_file_name)

# Single source of truth for schema; Alembic compares against this.
target_metadata = Base.metadata


def _sync_url(url: str) -> str:
    """Convert an async DB URL to its synchronous equivalent.

    Alembic's default :func:`engine_from_config` builds a sync engine, so we
    swap async drivers out. Pass-through if the URL is already sync.
    """
    if url.startswith("mysql+asyncmy://"):
        return url.replace("mysql+asyncmy://", "mysql+pymysql://", 1)
    if url.startswith("sqlite+aiosqlite://"):
        return url.replace("sqlite+aiosqlite://", "sqlite://", 1)
    return url


def run_migrations_offline() -> None:
    """Run migrations in 'offline' mode (emit SQL without a live connection)."""
    url = _sync_url(get_settings().db_url)
    # SQLite cannot ALTER most column properties directly; Alembic's batch mode
    # (table-recreate) handles it. Enable it for SQLite so the SAME migration
    # scripts run on both SQLite (dev/test) and MySQL (prod). MySQL needs no
    # batch mode and gets direct ALTERs.
    render_as_batch = url.startswith("sqlite")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
        compare_type=True,
        compare_server_default=True,
        render_as_batch=render_as_batch,
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online() -> None:
    """Run migrations in 'online' mode (open a connection, run, close)."""
    config.set_main_option("sqlalchemy.url", _sync_url(get_settings().db_url))

    connectable = engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        # See offline mode for the rationale on batch mode per dialect.
        render_as_batch = connection.dialect.name == "sqlite"
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
            compare_type=True,
            compare_server_default=True,
            render_as_batch=render_as_batch,
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()