# Copyright (c) 2023, NVIDIA CORPORATION. All rights reserved.

"""Megatron Module"""

import torch
from torch.autograd import Variable
from torch.nn.parameter import Parameter

from megatron.core import parallel_state, tensor_parallel
from megatron.core.transformer.transformer_config import TransformerConfig

_FLOAT_TYPES = (torch.FloatTensor, torch.cuda.FloatTensor)
_HALF_TYPES = (torch.HalfTensor, torch.cuda.HalfTensor)
_BF16_TYPES = (torch.BFloat16Tensor, torch.cuda.BFloat16Tensor)


def param_is_not_shared(param):
    return not hasattr(param, 'shared') or not param.shared


class MegatronModule(torch.nn.Module):
    """Megatron specific extensions of torch Module with support
    for pipelining."""

    # def __init__(self, config: TransformerConfig, share_word_embeddings=True):
    def __init__(self, config: TransformerConfig):
        super().__init__()
        self.config = config

    def state_dict_for_save_checkpoint(self, prefix='', keep_vars=False):
        """Use this function to override the state dict for
           saving checkpoints.
        """

        return self.state_dict(prefix=prefix, keep_vars=keep_vars)

    def sharded_state_dict(self, prefix=''):
        """ Override sharded_state_dict when using distributed checkpointing.
            keep_vars must always be set to True so that optimizer states
            can be sharded.
        """
        return self.state_dict(prefix=prefix, keep_vars=True)


def conversion_helper(val, conversion):
    """Apply conversion to val. Recursively apply conversion if `val`
    #is a nested tuple/list structure."""
    if not isinstance(val, (tuple, list)):
        return conversion(val)
    rtn = [conversion_helper(v, conversion) for v in val]
    if isinstance(val, tuple):
        rtn = tuple(rtn)
    return rtn


def fp32_to_float16(val, float16_convertor):
    """Convert fp32 `val` to fp16/bf16"""

    def half_conversion(val):
        val_typecheck = val
        if isinstance(val_typecheck, (Parameter, Variable)):
            val_typecheck = val.data
        if isinstance(val_typecheck, _FLOAT_TYPES):
            val = float16_convertor(val)
        return val

    return conversion_helper(val, half_conversion)


def float16_to_fp32(val):
    """Convert fp16/bf16 `val` to fp32"""

    def float_conversion(val):
        val_typecheck = val
        if isinstance(val_typecheck, (Parameter, Variable)):
            val_typecheck = val.data
        if isinstance(val_typecheck, (_BF16_TYPES, _HALF_TYPES)):
            val = val.float()
        return val

    return conversion_helper(val, float_conversion)


class Float16Module(MegatronModule):
    def __init__(self, config: TransformerConfig, module: torch.nn.Module):
        super(Float16Module, self).__init__(config)
        self.config = config
        self.fp16 = config.fp16
        self.bf16 = config.bf16

        if self.fp16:
            self.add_module('module', module.half())

            def float16_convertor(val):
                return val.half()

        elif self.bf16:
            self.add_module('module', module.bfloat16())

            def float16_convertor(val):
                return val.bfloat16()

        else:
            raise Exception('Either config.fp16 or config.bf16 should be True.')

        self.float16_convertor = float16_convertor

    def set_input_tensor(self, input_tensor):
        return self.module.set_input_tensor(input_tensor)

    def forward(self, *inputs, **kwargs):
        if parallel_state.is_pipeline_first_stage():
            inputs = fp32_to_float16(inputs, self.float16_convertor)
        outputs = self.module(*inputs, **kwargs)
        if parallel_state.is_pipeline_last_stage():
            outputs = float16_to_fp32(outputs)
        return outputs

    def state_dict(self, destination=None, prefix='', keep_vars=False):
        return self.module.state_dict(destination=destination, prefix=prefix, keep_vars=keep_vars)

    def state_dict_for_save_checkpoint(self, prefix='', keep_vars=False):
        """ Retrieve state_dict from the module being wrapped."""
        return self.module.state_dict_for_save_checkpoint(prefix=prefix, keep_vars=keep_vars)

    def sharded_state_dict(self, prefix=''):
        """ Retrieve sharded_state_dict from the module being wrapped.
        """
        return self.module.sharded_state_dict(prefix=prefix)

    def load_state_dict(self, state_dict, strict=True):
        self.module.load_state_dict(state_dict, strict=strict)
