import types
from ..fp16_utils import master_params_to_model_params
from ..multi_tensor_apply import multi_tensor_applier
from ._amp_state import maybe_print
import torch


class AmpOptimizerState(object):
    def __init__(self):
        pass


def lazy_init_with_master_weights(self):
        stash = self._amp_stash
        stash.fp16_groups = []
        stash.fp32_from_fp16_groups = []
        stash.fp32_from_fp32_groups = []
        for i, param_group in enumerate(self.param_groups):
            # maybe_print("FP16_Optimizer processing param group {}:".format(i))
            fp16_params_this_group = []
            fp32_params_this_group = []
            fp32_from_fp16_params_this_group = []
            for i, param in enumerate(param_group['params']):
                if param.requires_grad:
                    if param.type() == 'torch.cuda.HalfTensor':
                        # maybe_print("FP16_Optimizer received torch.cuda.HalfTensor with {}"
                        #             .format(param.size()))
                        fp16_params_this_group.append(param)
                        master_param = param.detach().clone().float()
                        master_param.requires_grad = True
                        param_group['params'][i] = master_param
                        fp32_from_fp16_params_this_group.append(master_param)
                        # Reset existing state dict key to the new master param.
                        # We still need to recast per-param state tensors, if any, to FP32.
                        if param in self.state:
                           self.state[master_param] = self.state.pop(param)
                    elif param.type() == 'torch.cuda.FloatTensor':
                        # maybe_print("FP16_Optimizer received torch.cuda.FloatTensor with {}"
                        #             .format(param.size()))
                        fp32_params_this_group.append(param)
                        param_group['params'][i] = param
                    else:
                        raise TypeError("Optimizer's parameters must be either "
                                        "torch.cuda.FloatTensor or torch.cuda.HalfTensor. "
                                        "Received {}".format(param.type()))

            stash.fp16_groups.append(fp16_params_this_group)
            stash.fp32_from_fp16_groups.append(fp32_from_fp16_params_this_group)
            stash.fp32_from_fp32_groups.append(fp32_params_this_group)

        stash.all_fp16_params = []
        for group in stash.fp16_groups:
            stash.all_fp16_params += group

        stash.all_fp32_from_fp16_params = []
        for group in stash.fp32_from_fp16_groups:
            stash.all_fp32_from_fp16_params += group

        stash.all_fp32_from_fp32_params = []
        for group in stash.fp32_from_fp32_groups:
            stash.all_fp32_from_fp32_params += group

        # stash.all_fp32_from_fp16_grad_stash = [None for _ in stash.all_fp32_from_fp16_params]
        stash.all_fp32_from_fp32_grad_stash = [None for _ in stash.all_fp32_from_fp32_params]

        for param in stash.all_fp32_from_fp16_params:
            param.grad = None

        for param in stash.all_fp32_from_fp32_params:
            param.grad = None

        # Leverage state_dict() and load_state_dict() to recast preexisting per-param state tensors
        self.load_state_dict(self.state_dict())


def prepare_backward_with_master_weights(self):
    stash = self._amp_stash

    if not stash.lazy_init_called:
        self._lazy_init_maybe_master_weights()
        stash.lazy_init_called = True

    for i, param in enumerate(stash.all_fp16_params):
        # Set up to leverage grad copy elision:
        param.grad = None

    # for i, param in enumerate(stash.all_fp32_from_fp16_params):
    #     stash.all_fp32_from_fp16_grad_stash[i] = param.grad

    for i, param in enumerate(stash.all_fp32_from_fp32_params):
        stash.all_fp32_from_fp32_grad_stash[i] = param.grad
        # Set up to leverage grad copy elision:
        param.grad = None


def post_backward_with_master_weights(self, scaler):
    stash = self._amp_stash

    # This is a lot of python overhead...
    fp16_grads_needing_unscale = []
    new_fp32_grads = []
    fp16_grads_needing_unscale_with_stash = []
    preexisting_fp32_grads = []
    for fp16_param, fp32_param in zip(stash.all_fp16_params,
                                      stash.all_fp32_from_fp16_params):
        if fp16_param.grad is None and fp32_param.grad is not None:
            continue
        elif fp16_param.grad is not None and fp32_param.grad is None:
            fp32_param.grad = torch.empty_like(fp32_param) 
            fp16_grads_needing_unscale.append(fp16_param.grad)
            new_fp32_grads.append(fp32_param.grad)
        elif fp16_param.grad is not None and fp32_param.grad is not None:
            fp16_grads_needing_unscale_with_stash.append(fp16_param.grad)
            preexisting_fp32_grads.append(fp32_param.grad)
        else: # fp16_param.grad is None and fp32_param.grad is None:
            continue

    if len(fp16_grads_needing_unscale) > 0:
        scaler.unscale(
            fp16_grads_needing_unscale,
            new_fp32_grads,
            scaler.loss_scale(),
            models_are_masters=False)

    if len(fp16_grads_needing_unscale_with_stash) > 0:
        scaler.unscale_with_stashed(
            fp16_grads_needing_unscale_with_stash,
            preexisting_fp32_grads,
            preexisting_fp32_grads)

    # fp32 params can be treated as they would be in the "no_master_weights" case.
    grads_needing_unscale = []
    grads_needing_unscale_with_stash = []
    stashed = []
    for param, stashed_grad in zip(stash.all_fp32_from_fp32_params,
                                   stash.all_fp32_from_fp32_grad_stash):
        if param.grad is None and stashed_grad is not None:
            param.grad = stashed_grad
        elif param.grad is not None and stashed_grad is None:
            grads_needing_unscale.append(param.grad)
        elif param.grad is not None and stashed_grad is not None:
            grads_needing_unscale_with_stash.append(param.grad)
            stashed.append(stashed_grad)
        else: # param.grad is None and stashed_grad is None:
            continue

    if len(grads_needing_unscale) > 0:
        scaler.unscale(
            grads_needing_unscale,
            grads_needing_unscale,
            scaler.loss_scale(),
            models_are_masters=True)

    if len(grads_needing_unscale_with_stash) > 0:
        scaler.unscale_with_stashed(
            grads_needing_unscale_with_stash,
            stashed,
            grads_needing_unscale_with_stash)

    # Clear the stash.
    for i in range(len(stash.all_fp32_from_fp32_grad_stash)):
        stash.all_fp32_from_fp32_grad_stash[i] = None


def lazy_init_no_master_weights(self):
    stash = self._amp_stash
    stash.all_fp16_params = []
    stash.all_fp32_params = []
    for i, param_group in enumerate(self.param_groups):
        for i, param in enumerate(param_group['params']):
            if param.type() == 'torch.cuda.HalfTensor':
                stash.all_fp16_params.append(param)
            elif param.type() == 'torch.cuda.FloatTensor':
                stash.all_fp32_params.append(param)
            else:
                raise TypeError("Optimizer's parameters must be either "
                                "torch.cuda.FloatTensor or torch.cuda.HalfTensor. "
                                "Received {}".format(param.type()))
    
    stash.all_fp16_grad_stash = [None for _ in stash.all_fp16_params]
    stash.all_fp32_grad_stash = [None for _ in stash.all_fp32_params]


def prepare_backward_no_master_weights(self):
    stash = self._amp_stash

    if not stash.lazy_init_called:
        self._lazy_init_maybe_master_weights()
        stash.lazy_init_called = True

    for i, param in enumerate(stash.all_fp16_params):
        stash.all_fp16_grad_stash[i] = param.grad
        # Set up to leverage grad copy elision:
        param.grad = None

    for i, param in enumerate(stash.all_fp32_params):
        stash.all_fp32_grad_stash[i] = param.grad
        # Set up to leverage grad copy elision:
        param.grad = None


def post_backward_no_master_weights(self, scaler):
    stash = self._amp_stash

    split_types = ((stash.all_fp16_params, stash.all_fp16_grad_stash),
             (stash.all_fp32_params, stash.all_fp32_grad_stash))

    for params, stashed_grads in split_types:
        # This is a lot of python overhead...
        grads_needing_unscale = []
        grads_needing_unscale_with_stash = []
        stashed = []
        for param, stashed_grad in zip(params, stashed_grads):
            if param.grad is None and stashed_grad is not None:
                param.grad = stashed_grad
            elif param.grad is not None and stashed_grad is None:
                grads_needing_unscale.append(param.grad)
            elif param.grad is not None and stashed_grad is not None:
                grads_needing_unscale_with_stash.append(param.grad)
                stashed.append(stashed_grad)
            else: # param.grad is None and stashed_grad is None
                continue

        if len(grads_needing_unscale) > 0:
            scaler.unscale(
                grads_needing_unscale,
                grads_needing_unscale,
                scaler.loss_scale(),
                models_are_masters=True)

        if len(grads_needing_unscale_with_stash) > 0:
            scaler.unscale_with_stashed(
                grads_needing_unscale_with_stash,
                stashed,
                grads_needing_unscale_with_stash)

        # Clear the stash.
        for i in range(len(stashed_grads)):
            stashed_grads[i] = None


def _master_params_to_model_params(self):
    stash = self._amp_stash
    if multi_tensor_applier.available:
        if len(stash.all_fp16_params) > 0:
            multi_tensor_applier(
                stash.multi_tensor_scale,
                stash.dummy_overflow_buf,
                [stash.all_fp32_from_fp16_params, stash.all_fp16_params],
                1.0)
    else:
        for fp16_group, fp32_from_fp16_group in zip(stash.fp16_groups, stash.fp32_from_fp16_groups):
            master_params_to_model_params(fp16_group, fp32_from_fp16_group)


def _process_optimizer(optimizer, properties):
    if hasattr(optimizer, "_amp_stash"):
        raise RuntimeError("A given optimizer should only be passed through amp.initialize once.")
    else:
        optimizer._amp_stash = AmpOptimizerState()

    optimizer._amp_stash.lazy_init_called = False
    optimizer._amp_stash.already_patched = False

    for name in ("_lazy_init_maybe_master_weights",
                 "_master_params_to_model_params",
                 "_prepare_amp_backward",
                 "_post_amp_backward"):
        if hasattr(optimizer, name):
            raise RuntimeError("Incoming optimizer already has {} defined.".format(name))

    # TODO:  Centralize exposure and import error checking for the C backend.
    if multi_tensor_applier.available:
        import amp_C
        optimizer._amp_stash.multi_tensor_scale = amp_C.multi_tensor_scale
        optimizer._amp_stash.dummy_overflow_buf = torch.cuda.IntTensor([0]);

    if properties.master_weights:
        optimizer._lazy_init_maybe_master_weights = types.MethodType(
            lazy_init_with_master_weights, optimizer)

        optimizer._master_params_to_model_params = types.MethodType(
            _master_params_to_model_params, optimizer)

        old_step = optimizer.step
        def new_step(self):
            retval = old_step()
            self._master_params_to_model_params()
            # Clear the master grads that wouldn't be zeroed by model.zero_grad()
            for param in self._amp_stash.all_fp32_from_fp16_params:
                param.grad = None
            return retval
        optimizer.step = types.MethodType(new_step, optimizer)

        old_zero_grad = optimizer.zero_grad
        def new_zero_grad(self):
            stash = self._amp_stash
            if not stash.lazy_init_called:
                self._lazy_init_maybe_master_weights()
                stash.lazy_init_called = True
            # Zero the model grads.
            for param in stash.all_fp16_params:
                if param.grad is not None:
                    param.grad.detach_()
                    param.grad.zero_()
            for param in stash.all_fp32_from_fp32_params:
                if param.grad is not None:
                    param.grad.detach_()
                    param.grad.zero_()
            # Clear the master grads that are independent of model grads
            for param in self._amp_stash.all_fp32_from_fp16_params:
                param.grad = None
        optimizer.zero_grad = types.MethodType(new_zero_grad, optimizer)

        optimizer._prepare_amp_backward = types.MethodType(
            prepare_backward_with_master_weights, optimizer)

        optimizer._post_amp_backward = types.MethodType(
            post_backward_with_master_weights, optimizer)
    else:
        optimizer._lazy_init_maybe_master_weights = types.MethodType(
            lazy_init_no_master_weights, optimizer)

        optimizer._prepare_amp_backward = types.MethodType(
            prepare_backward_no_master_weights, optimizer)

        optimizer._post_amp_backward = types.MethodType(
            post_backward_no_master_weights, optimizer)

    return optimizer
