"""Config for the protein folding model and experiment."""

from collections.abc import Mapping
import copy
import dataclasses
import types
import typing
from typing import Any, ClassVar, TypeVar


_T = TypeVar('_T')
_ConfigT = TypeVar('_ConfigT', bound='BaseConfig')


def _strip_optional(t: type[Any]) -> type[Any]:
  """Transforms type annotations of the form `T | None` to `T`."""
  if typing.get_origin(t) in (typing.Union, types.UnionType):
    args = set(typing.get_args(t)) - {types.NoneType}
    if len(args) == 1:
      return args.pop()
  return t


_NO_UPDATE = object()


class _Autocreate:

  def __init__(self, **defaults: Any):
    self.defaults = defaults


def autocreate(**defaults: Any) -> Any:
  """Marks a field as having a default factory derived from its type."""
  return _Autocreate(**defaults)


def _clone_field(
    field: dataclasses.Field[_T], new_default: _T
) -> dataclasses.Field[_T]:
  if new_default is _NO_UPDATE:
    return copy.copy(field)
  return dataclasses.field(
      default=new_default,
      init=True,
      kw_only=True,
      repr=field.repr,
      hash=field.hash,
      compare=field.compare,
      metadata=field.metadata,
  )


@typing.dataclass_transform()
class ConfigMeta(type):
  """Metaclass that synthesizes a __post_init__ that coerces dicts to Config subclass instances."""

  def __new__(mcs, name, bases, classdict):
    cls = super().__new__(mcs, name, bases, classdict)

    def _coercable_fields(self) -> Mapping[str, tuple[ConfigMeta, Any]]:
      type_hints = typing.get_type_hints(self.__class__)
      fields = dataclasses.fields(self.__class__)
      field_to_type_and_default = {
          field.name: (_strip_optional(type_hints[field.name]), field.default)
          for field in fields
      }
      coercable_fields = {
          f: t
          for f, t in field_to_type_and_default.items()
          if issubclass(type(t[0]), ConfigMeta)
      }
      return coercable_fields

    cls._coercable_fields = property(_coercable_fields)

    old_post_init = getattr(cls, '__post_init__', None)

    def _post_init(self) -> None:
      # Use get_type_hints instead of Field.type to ensure that forward
      # references are resolved.
      for field_name, (
          field_type,
          field_default,
      ) in self._coercable_fields.items():  # pylint: disable=protected-access
        field_value = getattr(self, field_name)
        if field_value is None:
          continue
        try:
          match field_value:
            case _Autocreate():
              # Construct from field defaults.
              setattr(self, field_name, field_type(**field_value.defaults))
            case Mapping():
              # Field value is not yet a `Config` instance; Assume we can create
              # one by splatting keys and values.
              args = {}
              # Apply default args first, if present.
              if isinstance(field_default, _Autocreate):
                args.update(field_default.defaults)
              args.update(field_value)
              setattr(self, field_name, field_type(**args))
            case _:
              pass
        except TypeError as e:
          raise TypeError(
              f'Failure while coercing field {field_name!r} of'
              f' {self.__class__.__qualname__}'
          ) from e
      if old_post_init:
        old_post_init(self)

    cls.__post_init__ = _post_init

    return dataclasses.dataclass(kw_only=True)(cls)


class BaseConfig(metaclass=ConfigMeta):
  """Config base class.

  Subclassing Config automatically makes the subclass a kw_only dataclass with
  a `__post_init__` that coerces Config-subclass field values from mappings to
  instances of the right type.
  """
  # Provided by dataclasses.make_dataclass
  __dataclass_fields__: ClassVar[dict[str, dataclasses.Field[Any]]]

  # Overridden by metaclass
  @property
  def _coercable_fields(self) -> Mapping[str, tuple[type['BaseConfig'], Any]]:
    return {}

  def as_dict(self) -> Mapping[str, Any]:
    result = dataclasses.asdict(self)
    for field_name in self._coercable_fields:
      field_value = getattr(self, field_name, None)
      if isinstance(field_value, BaseConfig):
        result[field_name] = field_value.as_dict()
    return result