import logging
from collections.abc import Callable, Sequence
from typing import Any, TypeVar

from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import DeclarativeBase

from ..db import get_transaction
from .enum import LoadStrategy
from .registry import Context, FixtureRegistry

logger = logging.getLogger(__name__)

T = TypeVar("T", bound=DeclarativeBase)


def get_obj_by_attr(
    fixtures: Callable[[], Sequence[T]], attr_name: str, value: Any
) -> T:
    """Get a SQLAlchemy model instance by matching an attribute value.

    Args:
        fixtures: A fixture function registered via ``@registry.register``
            that returns a sequence of SQLAlchemy model instances.
        attr_name: Name of the attribute to match against.
        value: Value to match.

    Returns:
        The first model instance where the attribute matches the given value.

    Raises:
        StopIteration: If no matching object is found.
    """
    return next(obj for obj in fixtures() if getattr(obj, attr_name) == value)


async def load_fixtures(
    session: AsyncSession,
    registry: FixtureRegistry,
    *names: str,
    strategy: LoadStrategy = LoadStrategy.MERGE,
) -> dict[str, list[DeclarativeBase]]:
    """Load specific fixtures by name with dependencies.

    Args:
        session: Database session
        registry: Fixture registry
        *names: Fixture names to load (dependencies auto-resolved)
        strategy: How to handle existing records

    Returns:
        Dict mapping fixture names to loaded instances

    Example:
        # Loads 'roles' first (dependency), then 'users'
        result = await load_fixtures(session, fixtures, "users")
        print(result["users"])  # [User(...), ...]
    """
    ordered = registry.resolve_dependencies(*names)
    return await _load_ordered(session, registry, ordered, strategy)


async def load_fixtures_by_context(
    session: AsyncSession,
    registry: FixtureRegistry,
    *contexts: str | Context,
    strategy: LoadStrategy = LoadStrategy.MERGE,
) -> dict[str, list[DeclarativeBase]]:
    """Load all fixtures for specific contexts.

    Args:
        session: Database session
        registry: Fixture registry
        *contexts: Contexts to load (e.g., Context.BASE, Context.TESTING)
        strategy: How to handle existing records

    Returns:
        Dict mapping fixture names to loaded instances

    Example:
        # Load base + testing fixtures
        await load_fixtures_by_context(
            session, fixtures,
            Context.BASE, Context.TESTING
        )
    """
    ordered = registry.resolve_context_dependencies(*contexts)
    return await _load_ordered(session, registry, ordered, strategy)


async def _load_ordered(
    session: AsyncSession,
    registry: FixtureRegistry,
    ordered_names: list[str],
    strategy: LoadStrategy,
) -> dict[str, list[DeclarativeBase]]:
    """Load fixtures in order."""
    results: dict[str, list[DeclarativeBase]] = {}

    for name in ordered_names:
        fixture = registry.get(name)
        instances = list(fixture.func())

        if not instances:
            results[name] = []
            continue

        model_name = type(instances[0]).__name__
        loaded: list[DeclarativeBase] = []

        async with get_transaction(session):
            for instance in instances:
                if strategy == LoadStrategy.INSERT:
                    session.add(instance)
                    loaded.append(instance)

                elif strategy == LoadStrategy.MERGE:
                    merged = await session.merge(instance)
                    loaded.append(merged)

                elif strategy == LoadStrategy.SKIP_EXISTING:
                    pk = _get_primary_key(instance)
                    if pk is not None:
                        existing = await session.get(type(instance), pk)
                        if existing is None:
                            session.add(instance)
                            loaded.append(instance)
                    else:
                        session.add(instance)
                        loaded.append(instance)

        results[name] = loaded
        logger.info(f"Loaded fixture '{name}': {len(loaded)} {model_name}(s)")

    return results


def _get_primary_key(instance: DeclarativeBase) -> Any | None:
    """Get the primary key value of a model instance."""
    mapper = instance.__class__.__mapper__
    pk_cols = mapper.primary_key

    if len(pk_cols) == 1:
        return getattr(instance, pk_cols[0].name, None)

    pk_values = tuple(getattr(instance, col.name, None) for col in pk_cols)
    if all(v is not None for v in pk_values):
        return pk_values
    return None