"""Scheduler registry and factory for instantiating learning rate schedulers."""

from typing import Dict, Callable, Optional
import torch.optim as optim
from torch.optim.lr_scheduler import LambdaLR
from taoTrain.config import TrainingConfig, SchedulerEnum


# Global registry for schedulers
_SCHEDULER_REGISTRY: Dict[str, Callable] = {}


def register_scheduler(name: str):
    """
    Decorator to register a custom scheduler factory function.
    
    Args:
        name: Name of the scheduler (e.g., 'linearWarmup', 'cosineWarmup', 'constant')
    """
    def decorator(fn: Callable) -> Callable:
        if name in _SCHEDULER_REGISTRY:
            raise ValueError(f"Scheduler '{name}' is already registered")
        _SCHEDULER_REGISTRY[name] = fn
        return fn
    return decorator


def get_registered_schedulers() -> Dict[str, Callable]:
    """Get all registered scheduler factory functions."""
    return _SCHEDULER_REGISTRY.copy()


def get_scheduler(
    optimizer: optim.Optimizer,
    config: TrainingConfig,
    num_training_steps: int,
) -> LambdaLR:
    """
    Create a learning rate scheduler instance from config.
    
    Args:
        optimizer: Optimizer to schedule learning rate for
        config: TrainingConfig with scheduler configuration
        num_training_steps: Total number of training steps
    
    Returns:
        Learning rate scheduler instance
    
    Raises:
        ValueError: If scheduler type is not registered
    """
    # Handle both enum and string values
    scheduler_type = config.scheduler.scheduler_type
    if isinstance(scheduler_type, str):
        scheduler_name = scheduler_type
    else:
        scheduler_name = scheduler_type.value
    
    if scheduler_name not in _SCHEDULER_REGISTRY:
        raise ValueError(
            f"Unknown scheduler: {scheduler_name}. "
            f"Available: {list(_SCHEDULER_REGISTRY.keys())}"
        )
    
    factory_fn = _SCHEDULER_REGISTRY[scheduler_name]
    return factory_fn(optimizer, config, num_training_steps)


def register_builtin_schedulers():
    """Register all built-in schedulers."""
    # Import here to trigger decorator registration (avoid circular imports)
    from . import linear_warmup  # noqa: F401
    from . import cosine_warmup  # noqa: F401
    from . import constant  # noqa: F401


# Auto-register built-in schedulers when module is imported
register_builtin_schedulers()