# -*- coding: utf-8 -*-
# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

import datetime
import itertools
import logging
import os
import tempfile
import time
from collections import Counter
import torch
from fvcore.common.checkpoint import PeriodicCheckpointer as _PeriodicCheckpointer
from fvcore.common.file_io import PathManager
from fvcore.common.timer import Timer
from fvcore.nn.precise_bn import get_bn_modules, update_bn_stats

import detectron2.utils.comm as comm
from detectron2.evaluation.testing import flatten_results_dict
from detectron2.utils.events import EventStorage, EventWriter

from .train_loop import HookBase

__all__ = [
    "CallbackHook",
    "IterationTimer",
    "PeriodicWriter",
    "PeriodicCheckpointer",
    "LRScheduler",
    "AutogradProfiler",
    "EvalHook",
    "PreciseBN",
]


"""
Implement some common hooks.
"""


class CallbackHook(HookBase):
    """
    Create a hook using callback functions provided by the user.
    """

    def __init__(self, *, before_train=None, after_train=None, before_step=None, after_step=None):
        """
        Each argument is a function that takes one argument: the trainer.
        """
        self._before_train = before_train
        self._before_step = before_step
        self._after_step = after_step
        self._after_train = after_train

    def before_train(self):
        if self._before_train:
            self._before_train(self.trainer)

    def after_train(self):
        if self._after_train:
            self._after_train(self.trainer)
        # The functions may be closures that hold reference to the trainer
        # Therefore, delete them to avoid circular reference.
        del self._before_train, self._after_train
        del self._before_step, self._after_step

    def before_step(self):
        if self._before_step:
            self._before_step(self.trainer)

    def after_step(self):
        if self._after_step:
            self._after_step(self.trainer)


class IterationTimer(HookBase):
    """
    Track the time spent for each iteration (each run_step call in the trainer).
    Print a summary in the end of training.

    This hook uses the time between the call to its :meth:`before_step`
    and :meth:`after_step` methods.
    Under the convention that :meth:`before_step` of all hooks should only
    take negligible amount of time, the :class:`IterationTimer` hook should be
    placed at the beginning of the list of hooks to obtain accurate timing.
    """

    def __init__(self, warmup_iter=3):
        """
        Args:
            warmup_iter (int): the number of iterations at the beginning to exclude
                from timing.
        """
        self._warmup_iter = warmup_iter
        self._step_timer = Timer()
        self._start_time = time.perf_counter()
        self._total_timer = Timer()

    def before_train(self):
        self._start_time = time.perf_counter()
        self._total_timer.reset()
        self._total_timer.pause()

    def after_train(self):
        logger = logging.getLogger(__name__)
        total_time = time.perf_counter() - self._start_time
        total_time_minus_hooks = self._total_timer.seconds()
        hook_time = total_time - total_time_minus_hooks

        num_iter = self.trainer.iter + 1 - self.trainer.start_iter - self._warmup_iter

        if num_iter > 0 and total_time_minus_hooks > 0:
            # Speed is meaningful only after warmup
            # NOTE this format is parsed by grep in some scripts
            logger.info(
                "Overall training speed: {} iterations in {} ({:.4f} s / it)".format(
                    num_iter,
                    str(datetime.timedelta(seconds=int(total_time_minus_hooks))),
                    total_time_minus_hooks / num_iter,
                )
            )

        logger.info(
            "Total training time: {} ({} on hooks)".format(
                str(datetime.timedelta(seconds=int(total_time))),
                str(datetime.timedelta(seconds=int(hook_time))),
            )
        )

    def before_step(self):
        self._step_timer.reset()
        self._total_timer.resume()

    def after_step(self):
        # +1 because we're in after_step
        iter_done = self.trainer.iter - self.trainer.start_iter + 1
        if iter_done >= self._warmup_iter:
            sec = self._step_timer.seconds()
            self.trainer.storage.put_scalars(time=sec)
        else:
            self._start_time = time.perf_counter()
            self._total_timer.reset()

        self._total_timer.pause()


class PeriodicWriter(HookBase):
    """
    Write events to EventStorage periodically.

    It is executed every ``period`` iterations and after the last iteration.
    """

    def __init__(self, writers, period=20):
        """
        Args:
            writers (list[EventWriter]): a list of EventWriter objects
            period (int):
        """
        self._writers = writers
        for w in writers:
            assert isinstance(w, EventWriter), w
        self._period = period

    def after_step(self):
        if (self.trainer.iter + 1) % self._period == 0 or (
            self.trainer.iter == self.trainer.max_iter - 1
        ):
            for writer in self._writers:
                writer.write()

    def after_train(self):
        for writer in self._writers:
            writer.close()


class PeriodicCheckpointer(_PeriodicCheckpointer, HookBase):
    """
    Same as :class:`detectron2.checkpoint.PeriodicCheckpointer`, but as a hook.

    Note that when used as a hook,
    it is unable to save additional data other than what's defined
    by the given `checkpointer`.

    It is executed every ``period`` iterations and after the last iteration.
    """

    def before_train(self):
        self.max_iter = self.trainer.max_iter

    def after_step(self):
        # No way to use **kwargs
        self.step(self.trainer.iter)


class LRScheduler(HookBase):
    """
    A hook which executes a torch builtin LR scheduler and summarizes the LR.
    It is executed after every iteration.
    """

    def __init__(self, optimizer, scheduler):
        """
        Args:
            optimizer (torch.optim.Optimizer):
            scheduler (torch.optim._LRScheduler)
        """
        self._optimizer = optimizer
        self._scheduler = scheduler

        # NOTE: some heuristics on what LR to summarize
        # summarize the param group with most parameters
        largest_group = max(len(g["params"]) for g in optimizer.param_groups)

        if largest_group == 1:
            # If all groups have one parameter,
            # then find the most common initial LR, and use it for summary
            lr_count = Counter([g["lr"] for g in optimizer.param_groups])
            lr = lr_count.most_common()[0][0]
            for i, g in enumerate(optimizer.param_groups):
                if g["lr"] == lr:
                    self._best_param_group_id = i
                    break
        else:
            for i, g in enumerate(optimizer.param_groups):
                if len(g["params"]) == largest_group:
                    self._best_param_group_id = i
                    break

    def after_step(self):
        lr = self._optimizer.param_groups[self._best_param_group_id]["lr"]
        self.trainer.storage.put_scalar("lr", lr, smoothing_hint=False)
        self._scheduler.step()


class AutogradProfiler(HookBase):
    """
    A hook which runs `torch.autograd.profiler.profile`.

    Examples:

    .. code-block:: python

        hooks.AutogradProfiler(
             lambda trainer: trainer.iter > 10 and trainer.iter < 20, self.cfg.OUTPUT_DIR
        )

    The above example will run the profiler for iteration 10~20 and dump
    results to ``OUTPUT_DIR``. We did not profile the first few iterations
    because they are typically slower than the rest.
    The result files can be loaded in the ``chrome://tracing`` page in chrome browser.

    Note:
        When used together with NCCL on older version of GPUs,
        autograd profiler may cause deadlock because it unnecessarily allocates
        memory on every device it sees. The memory management calls, if
        interleaved with NCCL calls, lead to deadlock on GPUs that do not
        support `cudaLaunchCooperativeKernelMultiDevice`.
    """

    def __init__(self, enable_predicate, output_dir, *, use_cuda=True):
        """
        Args:
            enable_predicate (callable[trainer -> bool]): a function which takes a trainer,
                and returns whether to enable the profiler.
                It will be called once every step, and can be used to select which steps to profile.
            output_dir (str): the output directory to dump tracing files.
            use_cuda (bool): same as in `torch.autograd.profiler.profile`.
        """
        self._enable_predicate = enable_predicate
        self._use_cuda = use_cuda
        self._output_dir = output_dir

    def before_step(self):
        if self._enable_predicate(self.trainer):
            self._profiler = torch.autograd.profiler.profile(use_cuda=self._use_cuda)
            self._profiler.__enter__()
        else:
            self._profiler = None

    def after_step(self):
        if self._profiler is None:
            return
        self._profiler.__exit__(None, None, None)
        PathManager.mkdirs(self._output_dir)
        out_file = os.path.join(
            self._output_dir, "profiler-trace-iter{}.json".format(self.trainer.iter)
        )
        if "://" not in out_file:
            self._profiler.export_chrome_trace(out_file)
        else:
            # Support non-posix filesystems
            with tempfile.TemporaryDirectory(prefix="detectron2_profiler") as d:
                tmp_file = os.path.join(d, "tmp.json")
                self._profiler.export_chrome_trace(tmp_file)
                with open(tmp_file) as f:
                    content = f.read()
            with PathManager.open(out_file, "w") as f:
                f.write(content)


class EvalHook(HookBase):
    """
    Run an evaluation function periodically, and at the end of training.

    It is executed every ``eval_period`` iterations and after the last iteration.
    """

    def __init__(self, eval_period, eval_function):
        """
        Args:
            eval_period (int): the period to run `eval_function`.
            eval_function (callable): a function which takes no arguments, and
                returns a nested dict of evaluation metrics.

        Note:
            This hook must be enabled in all or none workers.
            If you would like only certain workers to perform evaluation,
            give other workers a no-op function (`eval_function=lambda: None`).
        """
        self._period = eval_period
        self._func = eval_function

    def _do_eval(self):
        results = self._func()

        if results:
            assert isinstance(
                results, dict
            ), "Eval function must return a dict. Got {} instead.".format(results)

            flattened_results = flatten_results_dict(results)
            for k, v in flattened_results.items():
                try:
                    v = float(v)
                except Exception:
                    raise ValueError(
                        "[EvalHook] eval_function should return a nested dict of float. "
                        "Got '{}: {}' instead.".format(k, v)
                    )
            self.trainer.storage.put_scalars(**flattened_results, smoothing_hint=False)

        # Evaluation may take different time among workers.
        # A barrier make them start the next iteration together.
        comm.synchronize()

    def after_step(self):
        next_iter = self.trainer.iter + 1
        is_final = next_iter == self.trainer.max_iter
        if is_final or (self._period > 0 and next_iter % self._period == 0):
            self._do_eval()

    def after_train(self):
        # func is likely a closure that holds reference to the trainer
        # therefore we clean it to avoid circular reference in the end
        del self._func


class PreciseBN(HookBase):
    """
    The standard implementation of BatchNorm uses EMA in inference, which is
    sometimes suboptimal.
    This class computes the true average of statistics rather than the moving average,
    and put true averages to every BN layer in the given model.

    It is executed every ``period`` iterations and after the last iteration.
    """

    def __init__(self, period, model, data_loader, num_iter):
        """
        Args:
            period (int): the period this hook is run, or 0 to not run during training.
                The hook will always run in the end of training.
            model (nn.Module): a module whose all BN layers in training mode will be
                updated by precise BN.
                Note that user is responsible for ensuring the BN layers to be
                updated are in training mode when this hook is triggered.
            data_loader (iterable): it will produce data to be run by `model(data)`.
            num_iter (int): number of iterations used to compute the precise
                statistics.
        """
        self._logger = logging.getLogger(__name__)
        if len(get_bn_modules(model)) == 0:
            self._logger.info(
                "PreciseBN is disabled because model does not contain BN layers in training mode."
            )
            self._disabled = True
            return

        self._model = model
        self._data_loader = data_loader
        self._num_iter = num_iter
        self._period = period
        self._disabled = False

        self._data_iter = None

    def after_step(self):
        next_iter = self.trainer.iter + 1
        is_final = next_iter == self.trainer.max_iter
        if is_final or (self._period > 0 and next_iter % self._period == 0):
            self.update_stats()

    def update_stats(self):
        """
        Update the model with precise statistics. Users can manually call this method.
        """
        if self._disabled:
            return

        if self._data_iter is None:
            self._data_iter = iter(self._data_loader)

        def data_loader():
            for num_iter in itertools.count(1):
                if num_iter % 100 == 0:
                    self._logger.info(
                        "Running precise-BN ... {}/{} iterations.".format(num_iter, self._num_iter)
                    )
                # This way we can reuse the same iterator
                yield next(self._data_iter)

        with EventStorage():  # capture events in a new storage to discard them
            self._logger.info(
                "Running precise-BN for {} iterations...  ".format(self._num_iter)
                + "Note that this could produce different statistics every time."
            )
            update_bn_stats(self._model, data_loader(), self._num_iter)
