"""Alembic environment — reads DATABASE_URL from app config."""

import os
import re
from logging.config import fileConfig

from sqlalchemy import engine_from_config, pool, text

from alembic import context
from backend.app.config import get_config
from backend.app.models import Base

# Fail a blocked migration FAST instead of hanging forever. Migrations run
# against the live DB while workers hold locks; 0040's `ALTER series_page` queued
# behind a tag-merge that held a series_page lock for minutes (the merge runs an
# unindexed full scan over image_record while repointing series_page) and hung
# with no timeout — silent, indefinite (operator-flagged 2026-06-07). With a
# lock_timeout a blocked DDL errors ("canceling statement due to lock timeout")
# and the entrypoint's `alembic upgrade head` exits non-zero, so the deploy
# retries / surfaces loudly rather than wedging. Override via env when a known
# slow-lock window is expected.
_MIGRATION_LOCK_TIMEOUT = os.environ.get("MIGRATION_LOCK_TIMEOUT", "30s")
if not re.fullmatch(r"\d+\s*(ms|s|min)?", _MIGRATION_LOCK_TIMEOUT.strip()):
    _MIGRATION_LOCK_TIMEOUT = "30s"  # ignore a malformed override

config = context.config

if config.config_file_name is not None:
    fileConfig(config.config_file_name)

config.set_main_option("sqlalchemy.url", get_config().database_url_sync)

target_metadata = Base.metadata


def run_migrations_offline() -> None:
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
        compare_type=True,
    )
    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online() -> None:
    connectable = engine_from_config(
        config.get_section(config.config_ini_section, {}),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )
    with connectable.connect() as connection:
        # Session-level lock_timeout for every DDL statement in this run. Set
        # (and commit) before alembic opens its own transaction so the GUC
        # persists on this connection regardless of how alembic structures its
        # transactions. Value is from our own env, so f-string interpolation is
        # safe (and it's been pattern-validated above); SET takes no bind params.
        connection.execute(
            text(f"SET lock_timeout = '{_MIGRATION_LOCK_TIMEOUT}'")
        )
        connection.commit()
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
            compare_type=True,
        )
        with context.begin_transaction():
            context.run_migrations()


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