from keras_core.api_export import keras_core_export


@keras_core_export(
    ["keras_core.Initializer", "keras_core.initializers.Initializer"]
)
class Initializer:
    """Initializer base class: all Keras initializers inherit from this class.

    Initializers should implement a `__call__()` method with the following
    signature:

    ```python
    def __call__(self, shape, dtype=None, **kwargs):
        # returns a tensor of shape `shape` and dtype `dtype`
        # containing values drawn from a distribution of your choice.
    ```

    Optionally, you an also implement the method `get_config()` and the class
    method `from_config` in order to support serialization -- just like with
    any Keras object.

    Here's a simple example: a random normal initializer.

    ```python
    class ExampleRandomNormal(Initializer):
        def __init__(self, mean, stddev):
            self.mean = mean
            self.stddev = stddev

        def __call__(self, shape, dtype=None, **kwargs):
            return keras_core.random.normal(
                shape, mean=self.mean, stddev=self.stddev, dtype=dtype
            )

        def get_config(self):  # To support serialization
            return {"mean": self.mean, "stddev": self.stddev}
    ```

    Note that we don't have to implement `from_config()` in the example above
    since the constructor arguments of the class the keys in the config returned
    by `get_config()` are the same. In this case, the default `from_config()`
    works fine.
    """

    def __call__(self, shape, dtype=None):
        """Returns a tensor object initialized as specified by the initializer.

        Args:
            shape: Shape of the tensor.
            dtype: Optional dtype of the tensor.
        """
        raise NotImplementedError(
            "Initializer subclasses must implement the `__call__()` method."
        )

    def get_config(self):
        """Returns the initializer's configuration as a JSON-serializable dict.

        Returns:
            A JSON-serializable Python dict.
        """
        return {}

    @classmethod
    def from_config(cls, config):
        """Instantiates an initializer from a configuration dictionary.

        Example:

        ```python
        initializer = RandomUniform(-1, 1)
        config = initializer.get_config()
        initializer = RandomUniform.from_config(config)
        ```

        Args:
            config: A Python dictionary, the output of `get_config()`.

        Returns:
            An `Initializer` instance.
        """
        return cls(**config)