from pathlib import Path
import json
import copy
from typing import Iterable, Any
from contextlib import contextmanager

import torch


def save_args(basepath: Path, args, extra={}):
    info = {"args": vars(args)}
    info["args"].update(extra)
    with open(basepath.joinpath("args.json"), "w") as f:
        json.dump(info, f, indent=4)


class AverageMeter:
    avg: Any

    def __init__(self, name=None):
        self.name = name
        self.reset()

    def reset(self):
        self.sum = self.count = self.avg = 0

    def update(self, val, n=1):
        self.sum += val * n
        self.count += n
        self.avg = self.sum / self.count


# Adapted from torch-ema https://github.com/fadel/pytorch_ema/blob/master/torch_ema/ema.py#L14
class EMAModel:
    """
    Exponential Moving Average of models weights
    """

    def __init__(
        self,
        parameters: Iterable[torch.nn.Parameter],
        update_after_step: int = 0,
        inv_gamma: float = 1.0,
        power: float = 2 / 3,
        min_value: float = 0.0,
        max_value: float = 0.9999,
    ):
        """
        @crowsonkb's notes on EMA Warmup:
            If gamma=1 and power=1, implements a simple average. gamma=1, power=2/3 are good values for models you plan
            to train for a million or more steps (reaches decay factor 0.999 at 31.6K steps, 0.9999 at 1M steps),
            gamma=1, power=3/4 for models you plan to train for less (reaches decay factor 0.999 at 10K steps, 0.9999
            at 215.4k steps).
        Args:
            inv_gamma (float): Inverse multiplicative factor of EMA warmup. Default: 1.
            power (float): Exponential factor of EMA warmup. Default: 2/3.
            min_value (float): The minimum EMA decay rate. Default: 0.
        """
        parameters = list(parameters)
        self.shadow_params = [p.clone().detach() for p in parameters]

        self.collected_params = None

        self.update_after_step = update_after_step
        self.inv_gamma = inv_gamma
        self.power = power
        self.min_value = min_value
        self.max_value = max_value

        self.decay = 0.0
        self.optimization_step = 0

    def get_decay(self, optimization_step: int):
        """
        Compute the decay factor for the exponential moving average.
        """
        step = max(0, optimization_step - self.update_after_step - 1)
        value = 1 - (1 + step / self.inv_gamma) ** -self.power

        if step <= 0:
            return 0.0

        return max(self.min_value, min(value, self.max_value))

    @torch.no_grad()
    def step(self, parameters):
        parameters = list(parameters)

        self.optimization_step += 1

        # Compute the decay factor for the exponential moving average.
        self.decay = self.get_decay(self.optimization_step)

        for s_param, param in zip(self.shadow_params, parameters):
            if param.requires_grad:
                s_param.mul_(self.decay)
                s_param.add_(param.data, alpha=1 - self.decay)
            else:
                s_param.copy_(param)

        torch.cuda.empty_cache()

    def copy_to(self, parameters: Iterable[torch.nn.Parameter]) -> None:
        """
        Copy current averaged parameters into given collection of parameters.
        Args:
            parameters: Iterable of `torch.nn.Parameter`; the parameters to be
                updated with the stored moving averages. If `None`, the
                parameters with which this `ExponentialMovingAverage` was
                initialized will be used.
        """
        parameters = list(parameters)
        for s_param, param in zip(self.shadow_params, parameters):
            param.data.copy_(s_param.data)

    def to(self, device=None, dtype=None) -> None:
        r"""Move internal buffers of the ExponentialMovingAverage to `device`.
        Args:
            device: like `device` argument to `torch.Tensor.to`
        """
        # .to() on the tensors handles None correctly
        self.shadow_params = [
            p.to(device=device, dtype=dtype) if p.is_floating_point() else p.to(device=device)
            for p in self.shadow_params
        ]

    def state_dict(self) -> dict:
        r"""
        Returns the state of the ExponentialMovingAverage as a dict.
        This method is used by accelerate during checkpointing to save the ema state dict.
        """
        # Following PyTorch conventions, references to tensors are returned:
        # "returns a reference to the state and not its copy!" -
        # https://pytorch.org/tutorials/beginner/saving_loading_models.html#what-is-a-state-dict
        return {
            "decay": self.decay,
            "optimization_step": self.optimization_step,
            "shadow_params": self.shadow_params,
            "collected_params": self.collected_params,
        }

    def load_state_dict(self, state_dict: dict) -> None:
        r"""
        Loads the ExponentialMovingAverage state.
        This method is used by accelerate during checkpointing to save the ema state dict.
        Args:
            state_dict (dict): EMA state. Should be an object returned
                from a call to :meth:`state_dict`.
        """
        # deepcopy, to be consistent with module API
        state_dict = copy.deepcopy(state_dict)

        self.decay = state_dict["decay"]
        if self.decay < 0.0 or self.decay > 1.0:
            raise ValueError("Decay must be between 0 and 1")

        self.optimization_step = state_dict["optimization_step"]
        if not isinstance(self.optimization_step, int):
            raise ValueError("Invalid optimization_step")

        self.shadow_params = state_dict["shadow_params"]
        if not isinstance(self.shadow_params, list):
            raise ValueError("shadow_params must be a list")
        if not all(isinstance(p, torch.Tensor) for p in self.shadow_params):
            raise ValueError("shadow_params must all be Tensors")

        self.collected_params = state_dict["collected_params"]
        if self.collected_params is not None:
            if not isinstance(self.collected_params, list):
                raise ValueError("collected_params must be a list")
            if not all(isinstance(p, torch.Tensor) for p in self.collected_params):
                raise ValueError("collected_params must all be Tensors")
            if len(self.collected_params) != len(self.shadow_params):
                raise ValueError("collected_params and shadow_params must have the same length")

    @contextmanager
    def apply_temporary(self, parameters: Iterable[torch.nn.Parameter]):
        parameters = list(parameters)
        original_params = [p.clone() for p in parameters]
        self.copy_to(parameters)

        try:
            yield
        finally:
            for o_param, param in zip(original_params, parameters):
                param.data.copy_(o_param.data)
            del original_params