# Copyright 2024 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

"""Provides helpers for defining and working with the fields of IR data classes.

Field specs
-----------
Various utilities are provided for working with `dataclasses.Field`s:
  - Classes:
    - `FieldSpec` - used to track data about an IR data field
    - `FieldContainer` - used to track the field container type
  - Functions that work with `FieldSpec`s:
    - `make_field_spec`, `build_default`
  - Functions for retrieving a set of `FieldSpec`s for a given class:
    - `field_specs`
  - Functions for retrieving fields and their values:
    - `fields_and_values`
  - Functions for copying and updating IR data classes
    - `copy`, `update`
  - Functions to help defining IR data fields
    - `oneof_field`, `list_field`, `str_field`
"""

import dataclasses
import enum
import sys
from typing import (
    Any,
    Callable,
    ClassVar,
    ForwardRef,
    Iterable,
    Mapping,
    MutableMapping,
    NamedTuple,
    Optional,
    Protocol,
    SupportsIndex,
    Tuple,
    TypeVar,
    Union,
    cast,
    get_args,
    get_origin,
)


class IrDataclassInstance(Protocol):
  """Type bound for an IR dataclass instance."""

  __dataclass_fields__: ClassVar[dict[str, dataclasses.Field[Any]]]
  IR_DATACLASS: ClassVar[object]
  field_specs: ClassVar["FilteredIrFieldSpecs"]


IrDataT = TypeVar("IrDataT", bound=IrDataclassInstance)

CopyValuesListT = TypeVar("CopyValuesListT", bound=type)

_IR_DATACLASSS_ATTR = "IR_DATACLASS"


def _is_ir_dataclass(obj):
  return hasattr(obj, _IR_DATACLASSS_ATTR)


class CopyValuesList(list[CopyValuesListT]):
  """A list that makes copies of any value that is inserted"""

  def __init__(
      self, value_type: CopyValuesListT, iterable: Optional[Iterable] = None
  ):
    if iterable:
      super().__init__(iterable)
    else:
      super().__init__()
    self.value_type = value_type

  def _copy(self, obj: Any):
    if _is_ir_dataclass(obj):
      return copy(obj)
    return self.value_type(obj)

  def extend(self, iterable: Iterable) -> None:
    return super().extend([self._copy(i) for i in iterable])

  def shallow_copy(self, iterable: Iterable) -> None:
    """Explicitly performs a shallow copy of the provided list"""
    return super().extend(iterable)

  def append(self, obj: Any) -> None:
    return super().append(self._copy(obj))

  def insert(self, index: SupportsIndex, obj: Any) -> None:
    return super().insert(index, self._copy(obj))


class TemporaryCopyValuesList(NamedTuple):
  """Class used to temporarily hold a CopyValuesList while copying and
  constructing an IR dataclass.
  """

  temp_list: CopyValuesList


class FieldContainer(enum.Enum):
  """Indicates a fields container type"""

  NONE = 0
  OPTIONAL = 1
  LIST = 2


class FieldSpec(NamedTuple):
  """Indicates the container and type of a field.

  `FieldSpec` objects are accessed millions of times during runs so we cache as
  many operations as possible.
    - `is_dataclass`: `dataclasses.is_dataclass(data_type)`
    - `is_sequence`: `container is FieldContainer.LIST`
    - `is_enum`: `issubclass(data_type, enum.Enum)`
    - `is_oneof`: `oneof is not None`

  Use `make_field_spec` to automatically fill in the cached operations.
  """

  name: str
  data_type: type
  container: FieldContainer
  oneof: Optional[str]
  is_dataclass: bool
  is_sequence: bool
  is_enum: bool
  is_oneof: bool


def make_field_spec(
    name: str, data_type: type, container: FieldContainer, oneof: Optional[str]
):
  """Builds a field spec with cached type queries."""
  return FieldSpec(
      name,
      data_type,
      container,
      oneof,
      is_dataclass=_is_ir_dataclass(data_type),
      is_sequence=container is FieldContainer.LIST,
      is_enum=issubclass(data_type, enum.Enum),
      is_oneof=oneof is not None,
  )


def build_default(field_spec: FieldSpec):
  """Builds a default instance of the given field"""
  if field_spec.is_sequence:
    return CopyValuesList(field_spec.data_type)
  if field_spec.is_enum:
    return field_spec.data_type(int())
  return field_spec.data_type()


class FilteredIrFieldSpecs:
  """Provides cached views of an IR dataclass' fields."""

  def __init__(self, specs: Mapping[str, FieldSpec]):
    self.all_field_specs = specs
    self.field_specs = tuple(specs.values())
    self.dataclass_field_specs = {
        k: v for k, v in specs.items() if v.is_dataclass
    }
    self.oneof_field_specs = {k: v for k, v in specs.items() if v.is_oneof}
    self.sequence_field_specs = tuple(
        v for v in specs.values() if v.is_sequence
    )
    self.oneof_mappings = tuple(
        (k, v.oneof) for k, v in self.oneof_field_specs.items() if v.oneof
    )


def all_ir_classes(mod):
  """Retrieves a list of all IR dataclass definitions in the given module."""
  return (
      v
      for v in mod.__dict__.values()
      if isinstance(type, v.__class__) and _is_ir_dataclass(v)
  )


class IrDataclassSpecs:
  """Maintains a cache of all IR dataclass specs."""

  spec_cache: MutableMapping[type, FilteredIrFieldSpecs] = {}

  @classmethod
  def get_mod_specs(cls, mod):
    """Gets the IR dataclass specs for the given module."""
    return {
        ir_class: FilteredIrFieldSpecs(_field_specs(ir_class))
        for ir_class in all_ir_classes(mod)
    }

  @classmethod
  def get_specs(cls, data_class):
    """Gets the field specs for the given class. The specs will be cached."""
    if data_class not in cls.spec_cache:
      mod = sys.modules[data_class.__module__]
      cls.spec_cache.update(cls.get_mod_specs(mod))
    return cls.spec_cache[data_class]


def cache_message_specs(mod, cls):
  """Adds a cached `field_specs` attribute to IR dataclasses in `mod`
  excluding the given base `cls`.

  This needs to be done after the dataclass decorators run and create the
  wrapped classes.
  """
  for data_class in all_ir_classes(mod):
    if data_class is not cls:
      data_class.field_specs = IrDataclassSpecs.get_specs(data_class)


def _field_specs(cls: type[IrDataT]) -> Mapping[str, FieldSpec]:
  """Gets the IR data field names and types for the given IR data class"""
  # Get the dataclass fields
  class_fields = dataclasses.fields(cast(Any, cls))

  # Pre-python 3.11 (maybe pre 3.10) `get_type_hints` will substitute
  # `builtins.Expression` for 'Expression' rather than `ir_data.Expression`.
  # Instead we manually subsitute the type by extracting the list of classes
  # from the class' module and manually substituting.
  mod_ns = {
      k: v
      for k, v in sys.modules[cls.__module__].__dict__.items()
      if isinstance(type, v.__class__)
  }

  # Now extract the concrete type out of optionals
  result: MutableMapping[str, FieldSpec] = {}
  for class_field in class_fields:
    if class_field.name.startswith("_"):
      continue
    container_type = FieldContainer.NONE
    type_hint = class_field.type
    oneof = class_field.metadata.get("oneof")

    # Check if this type is wrapped
    origin = get_origin(type_hint)
    # Get the wrapped types if there are any
    args = get_args(type_hint)
    if origin is not None:
      # Extract the type.
      type_hint = args[0]

      # Underneath the hood `typing.Optional` is just a `Union[T, None]` so we
      # have to check if it's a `Union` instead of just using `Optional`.
      if origin == Union:
        # Make sure this is an `Optional` and not another `Union` type.
        assert len(args) == 2 and args[1] == type(None)
        container_type = FieldContainer.OPTIONAL
      elif origin == list:
        container_type = FieldContainer.LIST
      else:
        raise TypeError(f"Field has invalid container type: {origin}")

    # Resolve any forward references.
    if isinstance(type_hint, str):
      type_hint = mod_ns[type_hint]
    if isinstance(type_hint, ForwardRef):
      type_hint = mod_ns[type_hint.__forward_arg__]

    result[class_field.name] = make_field_spec(
        class_field.name, type_hint, container_type, oneof
    )

  return result


def field_specs(obj: Union[IrDataT, type[IrDataT]]) -> Mapping[str, FieldSpec]:
  """Retrieves the fields specs for the the give data type.

  The results of this method are cached to reduce lookup overhead.
  """
  cls = obj if isinstance(obj, type) else type(obj)
  if cls is type(None):
    raise TypeError("field_specs called with invalid type: NoneType")
  return IrDataclassSpecs.get_specs(cls).all_field_specs


def fields_and_values(
    ir: IrDataT,
    value_filt: Optional[Callable[[Any], bool]] = None,
):
  """Retrieves the fields and their values for a given IR data class.

  Args:
    ir: The IR data class or a read-only wrapper of an IR data class.
    value_filt: Optional filter used to exclude values.
  """
  set_fields: list[Tuple[FieldSpec, Any]] = []
  specs: FilteredIrFieldSpecs = ir.field_specs
  for spec in specs.field_specs:
    value = getattr(ir, spec.name)
    if not value_filt or value_filt(value):
      set_fields.append((spec, value))
  return set_fields


# `copy` is one of the hottest paths of embossc. We've taken steps to
# optimize this path at the expense of code clarity and modularization.
#
# 1. `FilteredFieldSpecs` are cached on in the class definition for IR
#    dataclasses under the `ir_data.Message.field_specs` class attribute. We
#    just assume the passed in object has that attribute.
# 2. We cache a `field_specs` entry that is just the `values()` of the
#    `all_field_specs` dict.
# 3. Copied lists are wrapped in a `TemporaryCopyValuesList`. This is used to
#    signal to consumers that they can take ownership of the contained list
#    rather than copying it again. See `ir_data.Message()` and `udpate()` for
#    where this is used.
# 4. `FieldSpec` checks are cached including `is_dataclass` and `is_sequence`.
# 5. None checks are only done in `copy()`, `_copy_set_fields` only
#    references `_copy()` to avoid this step.
def _copy_set_fields(ir: IrDataT):
  values: MutableMapping[str, Any] = {}

  specs: FilteredIrFieldSpecs = ir.field_specs
  for spec in specs.field_specs:
    value = getattr(ir, spec.name)
    if value is not None:
      if spec.is_sequence:
        if spec.is_dataclass:
          copy_value = CopyValuesList(spec.data_type, (_copy(v) for v in value))
          value = TemporaryCopyValuesList(copy_value)
        else:
          copy_value = CopyValuesList(spec.data_type, value)
          value = TemporaryCopyValuesList(copy_value)
      elif spec.is_dataclass:
        value = _copy(value)
      values[spec.name] = value
  return values


def _copy(ir: IrDataT) -> IrDataT:
  return type(ir)(**_copy_set_fields(ir))  # type: ignore[misc]


def copy(ir: IrDataT) -> Optional[IrDataT]:
  """Creates a copy of the given IR data class"""
  if not ir:
    return None
  return _copy(ir)


def update(ir: IrDataT, template: IrDataT):
  """Updates `ir`s fields with all set fields in the template."""
  for k, v in _copy_set_fields(template).items():
    if isinstance(v, TemporaryCopyValuesList):
      v = v.temp_list
    setattr(ir, k, v)


class OneOfField:
  """Decorator for a "oneof" field.

  Tracks when the field is set and will unset othe fields in the associated
  oneof group.

  Note: Decorators only work if dataclass slots aren't used.
  """

  def __init__(self, oneof: str) -> None:
    super().__init__()
    self.oneof = oneof
    self.owner_type = None
    self.proxy_name: str = ""
    self.name: str = ""

  def __set_name__(self, owner, name):
    self.name = name
    self.proxy_name = f"_{name}"
    self.owner_type = owner
    # Add our empty proxy field to the class.
    setattr(owner, self.proxy_name, None)

  def __get__(self, obj, objtype=None):
    return getattr(obj, self.proxy_name)

  def __set__(self, obj, value):
    if value is self:
      # This will happen if the dataclass uses the default value, we just
      # default to None.
      value = None

    if value is not None:
      # Clear the others
      for name, oneof in IrDataclassSpecs.get_specs(
          self.owner_type
      ).oneof_mappings:
        if oneof == self.oneof and name != self.name:
          setattr(obj, name, None)

    setattr(obj, self.proxy_name, value)


def oneof_field(name: str):
  """Alternative for `datclasses.field` that sets up a oneof variable"""
  return dataclasses.field(  # pylint:disable=invalid-field-call
      default=OneOfField(name), metadata={"oneof": name}, init=True
  )


def str_field():
  """Helper used to define a defaulted str field"""
  return dataclasses.field(default_factory=str)  # pylint:disable=invalid-field-call


def list_field(cls_or_fn):
  """Helper used to define a defaulted list field.

  A lambda can be used to defer resolution of a field type that references its
  container type, for example:
  ```
  class Foo:
    subtypes: list['Foo'] = list_field(lambda: Foo)
    names: list[str] = list_field(str)
  ```

  Args:
    cls_or_fn: The class type or a function that resolves to the class type.
  """

  def list_factory(c):
    return CopyValuesList(c if isinstance(c, type) else c())

  return dataclasses.field(  # pylint:disable=invalid-field-call
      default_factory=lambda: list_factory(cls_or_fn)
  )