# Copyright (c) Facebook, Inc. and its affiliates.
import itertools
import logging
import numpy as np
import operator
import pickle
import torch.utils.data
from tabulate import tabulate
from termcolor import colored

from detectron2.config import configurable
from detectron2.structures import BoxMode
from detectron2.utils.comm import get_world_size
from detectron2.utils.env import seed_all_rng
from detectron2.utils.file_io import PathManager
from detectron2.utils.logger import _log_api_usage, log_first_n

from detectron2.data.catalog import DatasetCatalog, MetadataCatalog
from detectron2.data.common import AspectRatioGroupedDataset, DatasetFromList, MapDataset
from detectron2.data.dataset_mapper import DatasetMapper
from detectron2.data.detection_utils import check_metadata_consistency
from detectron2.data.samplers import InferenceSampler, RepeatFactorTrainingSampler, TrainingSampler


"""
This file contains the default logic to build a dataloader for training or testing.
"""

__all__ = [
    "build_detection_train_loader",
]


# TODO can allow dataset as an iterable or IterableDataset to make this function more general
@configurable(from_config=_train_loader_from_config)
def build_detection_train_loader(
    dataset, *, mapper, sampler=None, total_batch_size, aspect_ratio_grouping=True, num_workers=0
):
    """
    Build a dataloader for object detection with some default features.
    This interface is experimental.

    Args:
        dataset (list or torch.utils.data.Dataset): a list of dataset dicts,
            or a map-style pytorch dataset. They can be obtained by using
            :func:`DatasetCatalog.get` or :func:`get_detection_dataset_dicts`.
        mapper (callable): a callable which takes a sample (dict) from dataset and
            returns the format to be consumed by the model.
            When using cfg, the default choice is ``DatasetMapper(cfg, is_train=True)``.
        sampler (torch.utils.data.sampler.Sampler or None): a sampler that produces
            indices to be applied on ``dataset``. Default to :class:`TrainingSampler`,
            which coordinates an infinite random shuffle sequence across all workers.
        total_batch_size (int): total batch size across all workers. Batching
            simply puts data into a list.
        aspect_ratio_grouping (bool): whether to group images with similar
            aspect ratio for efficiency. When enabled, it requires each
            element in dataset be a dict with keys "width" and "height".
        num_workers (int): number of parallel data loading workers

    Returns:
        torch.utils.data.DataLoader:
            a dataloader. Each output from it is a ``list[mapped_element]`` of length
            ``total_batch_size / num_workers``, where ``mapped_element`` is produced
            by the ``mapper``.
    """
    if isinstance(dataset, list):
        dataset = DatasetFromList(dataset, copy=False)
    if mapper is not None:
        dataset = MapDataset(dataset, mapper)
    if sampler is None:
        sampler = TrainingSampler(len(dataset))
    assert isinstance(sampler, torch.utils.data.sampler.Sampler)
    return build_batch_data_loader(
        dataset,
        sampler,
        total_batch_size,
        aspect_ratio_grouping=aspect_ratio_grouping,
        num_workers=num_workers,
    )


def _train_loader_from_config(cfg, mapper=None, *, dataset=None, sampler=None):
    if dataset is None:
        dataset = get_detection_dataset_dicts(
            cfg.DATASETS.TRAIN,
            filter_empty=cfg.DATALOADER.FILTER_EMPTY_ANNOTATIONS,
            min_keypoints=cfg.MODEL.ROI_KEYPOINT_HEAD.MIN_KEYPOINTS_PER_IMAGE
            if cfg.MODEL.KEYPOINT_ON
            else 0,
            proposal_files=cfg.DATASETS.PROPOSAL_FILES_TRAIN if cfg.MODEL.LOAD_PROPOSALS else None,
        )
        _log_api_usage("dataset." + cfg.DATASETS.TRAIN[0])

    if mapper is None:
        mapper = DatasetMapper(cfg, True)

    if sampler is None:
        sampler_name = cfg.DATALOADER.SAMPLER_TRAIN
        logger = logging.getLogger(__name__)
        logger.info("Using training sampler {}".format(sampler_name))
        if sampler_name == "TrainingSampler":
            sampler = TrainingSampler(len(dataset))
        elif sampler_name == "RepeatFactorTrainingSampler":
            repeat_factors = RepeatFactorTrainingSampler.repeat_factors_from_category_frequency(
                dataset, cfg.DATALOADER.REPEAT_THRESHOLD
            )
            sampler = RepeatFactorTrainingSampler(repeat_factors)
        else:
            raise ValueError("Unknown training sampler: {}".format(sampler_name))

    return {
        "dataset": dataset,
        "sampler": sampler,
        "mapper": mapper,
        "total_batch_size": cfg.SOLVER.IMS_PER_BATCH,
        "aspect_ratio_grouping": cfg.DATALOADER.ASPECT_RATIO_GROUPING,
        "num_workers": cfg.DATALOADER.NUM_WORKERS,
    }
