import torch


# needed for prefix-tuning of bloom model
def bloom_model_postprocess_past_key_value(past_key_values):
    past_key_values = torch.cat(past_key_values)
    total_layers, batch_size, num_attention_heads, num_virtual_tokens, head_dim = past_key_values.shape
    keys = past_key_values[: total_layers // 2]
    keys = keys.transpose(2, 3).reshape(
        total_layers // 2, batch_size * num_attention_heads, head_dim, num_virtual_tokens
    )
    values = past_key_values[total_layers // 2 :]
    values = values.reshape(total_layers // 2, batch_size * num_attention_heads, num_virtual_tokens, head_dim)

    return tuple(zip(keys, values))


def prepare_model_for_int8_training(
    model, output_embedding_layer_name="lm_head", use_gradient_checkpointing=True, layer_norm_names=["layer_norm"]
):
    r"""
    This method wrapps the entire protocol for preparing a model before running a training. This includes:
        1- Cast the layernorm in fp32 2- making output embedding layer require grads 3- Add the upcasting of the lm
        head to fp32

    Args:
        model, (`transformers.PreTrainedModel`):
            The loaded model from `transformers`
    """
    loaded_in_8bit = getattr(model, "is_loaded_in_8bit", False)

    for name, param in model.named_parameters():
        # freeze base model's layers
        param.requires_grad = False

        if loaded_in_8bit:
            # cast layer norm in fp32 for stability for 8bit models
            if param.ndim == 1 and any(layer_norm_name in name for layer_norm_name in layer_norm_names):
                param.data = param.data.to(torch.float32)

    if loaded_in_8bit and use_gradient_checkpointing:
        # For backward compatibility
        if hasattr(model, "enable_input_require_grads"):
            model.enable_input_require_grads()
        else:

            def make_inputs_require_grad(module, input, output):
                output.requires_grad_(True)

            model.get_input_embeddings().register_forward_hook(make_inputs_require_grad)

        # enable gradient checkpointing for memory efficiency
        model.gradient_checkpointing_enable()

    if hasattr(model, output_embedding_layer_name):
        output_embedding_layer = getattr(model, output_embedding_layer_name)
        input_dtype = output_embedding_layer.weight.dtype

        class CastOutputToFloat(torch.nn.Sequential):
            r"""
            Manually cast to the expected dtype of the lm_head as sometimes there is a final layer norm that is casted
            in fp32

            """

            def forward(self, x):
                return super().forward(x.to(input_dtype)).to(torch.float32)

        setattr(model, output_embedding_layer_name, CastOutputToFloat(output_embedding_layer))

    return model


TRANSFORMERS_MODELS_TO_PREFIX_TUNING_POSTPROCESS_MAPPING = {
    "bloom": bloom_model_postprocess_past_key_value,
}


# copied from transformers.models.bart.modeling_bart
def shift_tokens_right(input_ids: torch.Tensor, pad_token_id: int, decoder_start_token_id: int):
    """
    Shift input ids one token to the right.

    Args:
        input_ids (`torch.LongTensor` of shape `(batch_size, sequence_length)`): input ids
        pad_token_id (`int`): The id of the `padding` token.
        decoder_start_token_id (`int`): The id of the `start` token.
    """
    shifted_input_ids = input_ids.new_zeros(input_ids.shape)
    shifted_input_ids[:, 1:] = input_ids[:, :-1].clone()
    shifted_input_ids[:, 0] = decoder_start_token_id

    if pad_token_id is None:
        raise ValueError("self.model.config.pad_token_id has to be defined.")
    # replace possible -100 values in labels by `pad_token_id`
    shifted_input_ids.masked_fill_(shifted_input_ids == -100, pad_token_id)

    return shifted_input_ids


def _set_trainable(model):
    if model.modules_to_save is not None:
        for name, param in model.named_parameters():
            if any(module_name in name for module_name in model.modules_to_save):
                param.requires_grad = True


def fsdp_auto_wrap_policy(model):
    import functools
    import os

    from accelerate import FullyShardedDataParallelPlugin
    from torch.distributed.fsdp.wrap import _or_policy, lambda_auto_wrap_policy, transformer_auto_wrap_policy

    from ..tuners import PrefixEncoder, PromptEmbedding, PromptEncoder

    def lambda_policy_fn(module):
        if (
            len(list(module.named_children())) == 0
            and getattr(module, "weight", None) is not None
            and module.weight.requires_grad
        ):
            return True
        return False

    lambda_policy = functools.partial(lambda_auto_wrap_policy, lambda_fn=lambda_policy_fn)
    transformer_wrap_policy = functools.partial(
        transformer_auto_wrap_policy,
        transformer_layer_cls=(
            PrefixEncoder,
            PromptEncoder,
            PromptEmbedding,
            FullyShardedDataParallelPlugin.get_module_class_from_name(
                model, os.environ.get("FSDP_TRANSFORMER_CLS_TO_WRAP", "")
            ),
        ),
    )

    auto_wrap_policy = functools.partial(_or_policy, policies=[lambda_policy, transformer_wrap_policy])
    return auto_wrap_policy


def transpose(weight, fan_in_fan_out):
    return weight.T if fan_in_fan_out else weight
