"""Better brain parcellations for Region of Interest analysis."""

import collections.abc
import numbers
from copy import deepcopy

import numpy as np
from scipy.ndimage import label
from scipy.stats import scoreatpercentile

from nilearn import masking
from nilearn._utils.docs import fill_doc
from nilearn._utils.helpers import rename_parameters
from nilearn._utils.ndimage import peak_local_max
from nilearn._utils.niimg import safe_get_data
from nilearn._utils.niimg_conversions import (
    check_niimg,
    check_niimg_3d,
    check_niimg_4d,
    check_same_fov,
)
from nilearn._utils.param_validation import check_params
from nilearn._utils.segmentation import random_walker
from nilearn.image.image import (
    concat_imgs,
    new_img_like,
    smooth_array,
    threshold_img,
)
from nilearn.image.resampling import resample_img
from nilearn.maskers import NiftiMapsMasker


def _threshold_maps_ratio(maps_img, threshold):
    """Automatic thresholding of atlas maps image.

    Considers the given threshold as a ratio to the total number of voxels
    in the brain volume. This gives a certain number within the data
    voxel size which means that nonzero voxels which fall above than this
    size will be kept across all the maps.

    Parameters
    ----------
    maps_img : Niimg-like object
        An image of brain atlas maps.

    threshold : float
        If float, value is used as a ratio to n_voxels
        to get a certain threshold size in number to threshold the image.
        The value should be positive and
        within the range of number of maps (i.e. n_maps in 4th dimension).

    Returns
    -------
    threshold_maps_img : Nifti1Image
        Gives us thresholded image.

    """
    maps = check_niimg(maps_img)
    n_maps = maps.shape[-1]
    if (
        not isinstance(threshold, numbers.Real)
        or threshold <= 0
        or threshold > n_maps
    ):
        raise ValueError(
            "threshold given as ratio to the number of voxels must "
            "be Real number and should be positive and between 0 and "
            f"total number of maps i.e. n_maps={n_maps}. "
            f"You provided {threshold}"
        )
    else:
        ratio = threshold

    # Get a copy of the data
    maps_data = safe_get_data(maps, ensure_finite=True, copy_data=True)

    abs_maps = np.abs(maps_data)
    # thresholding
    cutoff_threshold = scoreatpercentile(
        abs_maps, 100.0 - (100.0 / n_maps) * ratio
    )
    maps_data[abs_maps < cutoff_threshold] = 0.0

    threshold_maps_img = new_img_like(maps, maps_data)

    return threshold_maps_img


def _remove_small_regions(input_data, affine, min_size):
    """Remove small regions in volume from input_data of specified min_size.

    min_size should be specified in mm^3 (region size in volume).

    Parameters
    ----------
    input_data : numpy.ndarray
        Values inside the regions defined by labels contained in input_data
        are summed together to get the size and compare with given min_size.
        For example, see scipy.ndimage.label.

    affine : numpy.ndarray
        Affine of input_data is used to convert size in voxels to size in
        volume of region in mm^3.

    min_size : float in mm^3
        Size of regions in input_data which falls below the specified min_size
        of volume in mm^3 will be discarded.

    Returns
    -------
    out : numpy.ndarray
        Data returned will have regions removed specified by min_size
        Otherwise, if criterion is not met then same input data will be
        returned.

    """
    # with return_counts argument is introduced from numpy 1.9.0.
    # _, region_sizes = np.unique(input_data, return_counts=True)

    # For now, to count the region sizes, we use return_inverse from
    # np.unique and then use np.bincount to count the region sizes.

    _, region_indices = np.unique(input_data, return_inverse=True)
    region_sizes = np.bincount(region_indices.ravel())
    size_in_vox = min_size / np.abs(np.linalg.det(affine[:3, :3]))
    labels_kept = region_sizes > size_in_vox
    if not np.all(labels_kept):
        # Put to zero the indices not kept
        rejected_labels_mask = np.isin(
            input_data, np.where(np.logical_not(labels_kept))[0]
        ).reshape(input_data.shape)
        # Avoid modifying the input:
        input_data = input_data.copy()
        input_data[rejected_labels_mask] = 0
        # Reorder the indices to avoid gaps
        input_data = np.searchsorted(np.unique(input_data), input_data)
    return input_data


@fill_doc
def connected_regions(
    maps_img,
    min_region_size=1350,
    extract_type="local_regions",
    smoothing_fwhm=6,
    mask_img=None,
):
    """Extract brain connected regions into separate regions.

    .. note::
        The region size should be defined in mm^3.
        See the documentation for more details.

    .. versionadded:: 0.2

    Parameters
    ----------
    maps_img : Niimg-like object
        An image of brain activation or atlas maps to be extracted into set of
        separate brain regions.

    min_region_size : :obj:`float`, default=1350
        Minimum volume in mm3 for a region to be kept.
        For example, if the :term:`voxel` size is 3x3x3 mm
        then the volume of the :term:`voxel` is 27mm^3.
        Default=1350mm^3, which means
        we take minimum size of 1350 / 27 = 50 voxels.
    %(extract_type)s
    %(smoothing_fwhm)s
        Use this parameter to smooth an image to extract most sparser regions.

        .. note::

            This parameter is passed to `nilearn.image.image.smooth_array`.
            It will be used only if ``extract_type='local_regions'``.

        Default=6.

    mask_img : Niimg-like object, default=None
        If given, mask image is applied to input data.
        If None, no masking is applied.

    Returns
    -------
    regions_extracted_img : :class:`nibabel.nifti1.Nifti1Image`
        Gives the image in 4D of extracted brain regions.
        Each 3D image consists of only one separated region.

    index_of_each_map : :class:`numpy.ndarray`
        An array of list of indices where each index denotes the identity
        of each extracted region to their family of brain maps.

    See Also
    --------
    nilearn.regions.connected_label_regions : A function can be used for
        extraction of regions on labels based atlas images.

    nilearn.regions.RegionExtractor : A class can be used for both
        region extraction on continuous type atlas images and
        also time series signals extraction from regions extracted.
    """
    all_regions_imgs = []
    index_of_each_map = []
    maps_img = check_niimg(maps_img, atleast_4d=True)
    maps = safe_get_data(maps_img, copy_data=True)
    affine = maps_img.affine
    min_region_size = min_region_size / np.abs(np.linalg.det(affine[:3, :3]))

    allowed_extract_types = ["connected_components", "local_regions"]
    if extract_type not in allowed_extract_types:
        message = (
            "'extract_type' should be given "
            f"either of these {allowed_extract_types} "
            f"You provided extract_type='{extract_type}'"
        )
        raise ValueError(message)

    if mask_img is not None:
        if not check_same_fov(maps_img, mask_img):
            # TODO (nilearn >= 0.13.0) force_resample=True
            mask_img = resample_img(
                mask_img,
                target_affine=maps_img.affine,
                target_shape=maps_img.shape[:3],
                interpolation="nearest",
                copy_header=True,
                force_resample=False,
            )
        mask_data, _ = masking.load_mask_img(mask_img)
        # Set as 0 to the values which are outside of the mask
        maps[mask_data == 0.0] = 0.0

    for index in range(maps.shape[-1]):
        regions = []
        map_3d = maps[..., index]
        # Mark the seeds using random walker
        if extract_type == "local_regions":
            smooth_map = smooth_array(
                map_3d, affine=affine, fwhm=smoothing_fwhm
            )
            seeds = peak_local_max(smooth_map)
            seeds_label, _ = label(seeds)
            # Assign -1 to values which are 0. to indicate to ignore
            seeds_label[map_3d == 0.0] = -1
            rw_maps = random_walker(map_3d, seeds_label)
            # Now simply replace "-1" with "0" for regions separation
            rw_maps[rw_maps == -1] = 0.0
            label_maps = rw_maps
        else:
            # Connected component extraction
            label_maps, n_labels = label(map_3d)

        # Takes the size of each labelized region data
        labels_size = np.bincount(label_maps.ravel())
        # set background labels sitting in zero index to zero
        labels_size[0] = 0.0
        for label_id, label_size in enumerate(labels_size):
            if label_size > min_region_size:
                region_data = (label_maps == label_id) * map_3d
                region_img = new_img_like(maps_img, region_data)
                regions.append(region_img)

        index_of_each_map.extend([index] * len(regions))
        all_regions_imgs.extend(regions)

    regions_extracted_img = concat_imgs(all_regions_imgs)

    return regions_extracted_img, index_of_each_map


@fill_doc
class RegionExtractor(NiftiMapsMasker):
    """Class for brain region extraction.

    Region Extraction is a post processing technique which
    is implemented to automatically segment each brain atlas maps
    into different set of separated brain activated region.
    Particularly, to show that each decomposed brain maps can be
    used to focus on a target specific Regions of Interest analysis.

    See :footcite:t:`Abraham2014`.

    .. versionadded:: 0.2

    Parameters
    ----------
    maps_img : 4D Niimg-like object or None, default=None
        Image containing a set of whole brain atlas maps or statistically
        decomposed brain maps.

    mask_img : Niimg-like object or None, optional
        Mask to be applied to input data, passed to NiftiMapsMasker.
        If None, no masking is applied.

    min_region_size : :obj:`float`, default=1350
        Minimum volume in mm3 for a region to be kept.
        For example, if the voxel size is 3x3x3 mm
        then the volume of the voxel is 27mm^3.
        The default of 1350mm^3 means
        we take minimum size of 1350 / 27 = 50 voxels.

    threshold : number, default=1.0
        A value used either in ratio_n_voxels or img_value or percentile
        `thresholding_strategy` based upon the choice of selection.

    thresholding_strategy : :obj:`str` \
                            {'ratio_n_voxels', 'img_value', 'percentile'}, \
                            default='ratio_n_voxels'
        If default 'ratio_n_voxels', we apply thresholding that will keep
        the more intense nonzero brain voxels (denoted as n_voxels)
        across all maps (n_voxels being the number of voxels in the brain
        volume). A float value given in `threshold` parameter indicates
        the ratio of voxels to keep meaning (if float=2. then maps will
        together have 2. x n_voxels non-zero voxels). If set to
        'percentile', images are thresholded based on the score obtained
        with the given percentile on the data and the voxel intensities
        which are survived above this obtained score will be kept. If set
        to 'img_value', we apply thresholding based on the non-zero voxel
        intensities across all maps. A value given in `threshold`
        parameter indicates that we keep only those voxels which have
        intensities more than this value.

    two_sided : :obj:`bool`, default=False
        Whether the thresholding should yield both positive and negative
        part of the maps.

        .. versionadded:: 0.11.1

    %(extractor)s

    %(smoothing_fwhm)s
        Use this parameter to smooth an image
        to extract most sparser regions.

        .. note::

            This parameter is passed to
            :func:`nilearn.regions.connected_regions`.
            It will be used only if ``extractor='local_regions'``.

        .. note::

            Please set this parameter according to maps resolution,
            otherwise extraction will fail.

        Default=6mm.

    %(standardize_false)s

        .. note::
            Recommended to set to True if signals are not already standardized.
            Passed to :class:`~nilearn.maskers.NiftiMapsMasker`.

    %(standardize_confounds)s

    high_variance_confounds : :obj:`bool`, default=False
        If True, high variance confounds are computed on provided image with
        :func:`nilearn.image.high_variance_confounds` and default parameters
        and regressed out.

    %(detrend)s

        .. note::
            Passed to :func:`nilearn.signal.clean`.

        Default=False.

    %(low_pass)s

        .. note::
            Passed to :func:`nilearn.signal.clean`.

    %(high_pass)s

        .. note::
            Passed to :func:`nilearn.signal.clean`.

    %(t_r)s

        .. note::
            Passed to :func:`nilearn.signal.clean`.

    %(dtype)s

    resampling_target : {"data", "mask", "maps", None}, default="data"
        Defines which image gives the final shape/size.

        - ``"data"`` means that the atlas is resampled
          to the shape of the data if needed
        - ``"mask"`` means that the ``maps_img`` and images provided
          to ``fit()`` are
          resampled to the shape and affine of ``mask_img``
        - ``"maps"`` means the ``mask_img`` and images provided
          to ``fit()`` are
          resampled to the shape and affine of ``maps_img``
        - ``None`` means no resampling: if shapes and affines do not match,
          a :obj:`ValueError` is raised.

    %(keep_masked_maps)s

    %(memory)s

    %(memory_level)s

    %(verbose0)s

    reports : :obj:`bool`, default=True
        If set to True, data is saved in order to produce a report.

    %(cmap)s
        default="CMRmap_r"
        Only relevant for the report figures.

    allow_overlap : True
        If False, an error is raised if the maps overlaps
        (ie at least two maps have a non-zero value for the same voxel).

    %(clean_args)s
        .. versionadded:: 0.12.1

    Attributes
    ----------
    %(clean_args_)s

    %(masker_kwargs_)s

    index_ : :class:`numpy.ndarray`
        Array of list of indices where each index value is assigned to
        each separate region of its corresponding family of brain maps.

    maps_img_ : :obj:`nibabel.nifti1.Nifti1Image`
        The maps mask of the data.

    %(nifti_mask_img_)s

    memory_ : joblib memory cache

    n_elements_ : :obj:`int`
        The number of overlapping maps in the mask.
        This is equivalent to the number of volumes in the mask image.

        .. versionadded:: 0.9.2

    regions_img_ : :class:`nibabel.nifti1.Nifti1Image`
        List of separated regions with each region lying on an
        original volume concatenated into a 4D image.

    References
    ----------
    .. footbibliography::

    See Also
    --------
    nilearn.regions.connected_label_regions : A function can be readily
        used for extraction of regions on labels based atlas images.

    """

    def __init__(
        self,
        maps_img=None,
        mask_img=None,
        min_region_size=1350,
        threshold=1.0,
        thresholding_strategy="ratio_n_voxels",
        two_sided=False,
        extractor="local_regions",
        smoothing_fwhm=6,
        standardize=False,
        standardize_confounds=True,
        high_variance_confounds=False,
        detrend=False,
        low_pass=None,
        high_pass=None,
        t_r=None,
        dtype=None,
        resampling_target="data",
        keep_masked_maps=True,
        memory=None,
        memory_level=0,
        verbose=0,
        reports=True,
        cmap="CMRmap_r",
        allow_overlap=True,
        clean_args=None,
    ):
        super().__init__(
            maps_img=maps_img,
            mask_img=mask_img,
            smoothing_fwhm=smoothing_fwhm,
            standardize=standardize,
            standardize_confounds=standardize_confounds,
            high_variance_confounds=high_variance_confounds,
            detrend=detrend,
            low_pass=low_pass,
            high_pass=high_pass,
            t_r=t_r,
            dtype=dtype,
            resampling_target=resampling_target,
            keep_masked_maps=keep_masked_maps,
            memory=memory,
            memory_level=memory_level,
            verbose=verbose,
            reports=reports,
            cmap=cmap,
            clean_args=clean_args,
            allow_overlap=allow_overlap,
        )
        self.maps_img = maps_img
        self.min_region_size = min_region_size
        self.thresholding_strategy = thresholding_strategy
        self.threshold = threshold
        self.two_sided = two_sided
        self.extractor = extractor
        self.smoothing_fwhm = smoothing_fwhm

    # TODO (nilearn >= 0.13.0)
    @fill_doc
    @rename_parameters(replacement_params={"X": "imgs"}, end_version="0.13.0")
    def fit(self, imgs=None, y=None):
        """Prepare signal extraction from regions.

        Parameters
        ----------
        imgs : :obj:`list` of Niimg-like objects or None, default=None
            See :ref:`extracting_data`.
            Image data passed to the reporter.

        %(y_dummy)s
        """
        del y
        check_params(self.__dict__)
        maps_img = deepcopy(self.maps_img)
        maps_img = check_niimg_4d(maps_img)

        self.mask_img_ = self._load_mask(imgs)

        if imgs is not None:
            check_niimg(imgs)

        list_of_strategies = ["ratio_n_voxels", "img_value", "percentile"]
        if self.thresholding_strategy not in list_of_strategies:
            message = (
                "'thresholding_strategy' should be "
                f"either of these {list_of_strategies}"
            )
            raise ValueError(message)

        if self.threshold is None or isinstance(self.threshold, str):
            raise ValueError(
                "The given input to threshold is not valid. "
                "Please submit a valid number specific to either of "
                f"the strategy in {list_of_strategies}"
            )
        elif isinstance(self.threshold, numbers.Number):
            # foreground extraction
            if self.thresholding_strategy == "ratio_n_voxels":
                threshold_maps = _threshold_maps_ratio(
                    maps_img, self.threshold
                )
            else:
                if self.thresholding_strategy == "percentile":
                    self.threshold = f"{self.threshold}%"
                threshold_maps = threshold_img(
                    maps_img,
                    mask_img=self.mask_img_,
                    copy=True,
                    threshold=self.threshold,
                    two_sided=self.two_sided,
                    copy_header=True,
                )

        # connected component extraction
        self.regions_img_, self.index_ = connected_regions(
            threshold_maps,
            self.min_region_size,
            self.extractor,
            self.smoothing_fwhm,
            mask_img=self.mask_img_,
        )

        self._fit_cache()

        self._maps_img = self.regions_img_
        super().fit(imgs)

        return self


def connected_label_regions(
    labels_img, min_size=None, connect_diag=True, labels=None
):
    """Extract connected regions from a brain atlas image \
    defined by labels (integers).

    For each label in a :term:`parcellation`, separates out connected
    components and assigns to each separated region a unique label.

    Parameters
    ----------
    labels_img : Nifti-like image
        A 3D image which contains regions denoted as labels. Each region
        is assigned with integers.

    min_size : :obj:`float`, default=None
        Minimum region size (in mm^3) in volume required
        to keep after extraction.
        Removes small or spurious regions.

    connect_diag : :obj:`bool`, default=True
        If 'connect_diag' is True, two voxels are considered in the same region
        if they are connected along the diagonal (26-connectivity). If it is
        False, two voxels are considered connected only if they are within the
        same x, y, or z direction.

    labels : 1D :class:`numpy.ndarray` or :obj:`list` of :obj:`str`, \
        default=None
        Each string in a list or array denote the name of the brain atlas
        regions given in labels_img input. If provided, same names will be
        re-assigned corresponding to each connected component based extraction
        of regions relabelling. The total number of names should match with the
        number of labels assigned in the image.

    Notes
    -----
    The order of the names given in labels should be appropriately matched with
    the unique labels (integers) assigned to each region given in labels_img
    (also excluding 'Background' label).

    Returns
    -------
    new_labels_img : :class:`nibabel.nifti1.Nifti1Image`
        A new image comprising of regions extracted on an input labels_img.

    new_labels : :obj:`list`, optional
        If labels are provided, new labels assigned to region extracted will
        be returned. Otherwise, only new labels image will be returned.

    See Also
    --------
    nilearn.datasets.fetch_atlas_harvard_oxford : For an example of atlas with
        labels.

    nilearn.regions.RegionExtractor : A class can be used for region extraction
        on continuous type atlas images.

    nilearn.regions.connected_regions : A function used for region extraction
        on continuous type atlas images.

    """
    labels_img = check_niimg_3d(labels_img)
    labels_data = safe_get_data(labels_img, ensure_finite=True)
    affine = labels_img.affine

    check_unique_labels = np.unique(labels_data)

    if min_size is not None and not isinstance(min_size, numbers.Number):
        raise ValueError(
            "Expected 'min_size' to be specified as integer. "
            f"You provided {min_size}"
        )
    if not isinstance(connect_diag, bool):
        raise ValueError(
            "'connect_diag' must be specified as True or False. "
            f"You provided {connect_diag}"
        )
    if np.any(check_unique_labels < 0):
        raise ValueError(
            "The 'labels_img' you provided has unknown/negative "
            f"integers as labels {check_unique_labels} assigned to regions. "
            "All regions in an image should have positive "
            "integers assigned as labels."
        )

    unique_labels = set(check_unique_labels)
    # check for background label indicated as 0
    if np.any(check_unique_labels == 0):
        unique_labels.remove(0)

    if labels is not None:
        if not isinstance(labels, collections.abc.Iterable) or isinstance(
            labels, str
        ):
            labels = [labels]
        if len(unique_labels) != len(labels):
            raise ValueError(
                f"The number of labels: {len(labels)} provided as input "
                f"in labels={labels} does not match with the number "
                f"of unique labels in labels_img: {len(unique_labels)}. "
                "Please provide appropriate match with unique "
                "number of labels in labels_img."
            )
        new_names = []

    this_labels = [None] * len(unique_labels) if labels is None else labels

    new_labels_data = np.zeros(labels_data.shape, dtype=np.int32)
    current_max_label = 0
    for label_id, name in zip(unique_labels, this_labels):
        this_label_mask = labels_data == label_id
        # Extract regions assigned to each label id
        if connect_diag:
            structure = np.ones((3, 3, 3), dtype=np.int32)
            regions, this_n_labels = label(
                this_label_mask.astype(np.int32), structure=structure
            )
        else:
            regions, this_n_labels = label(this_label_mask.astype(np.int32))

        if min_size is not None:
            regions = _remove_small_regions(regions, affine, min_size=min_size)
            this_n_labels = regions.max()

        cur_regions = regions[regions != 0] + current_max_label
        new_labels_data[regions != 0] = cur_regions
        current_max_label += this_n_labels
        if name is not None:
            new_names.extend([name] * this_n_labels)

    new_labels_img = new_img_like(labels_img, new_labels_data, affine=affine)

    return (
        (new_labels_img, new_names) if labels is not None else new_labels_img
    )
