# -*- coding: utf-8 -*-
# emacs: -*- mode: python; py-indent-offset: 4; indent-tabs-mode: nil -*-
# vi: set ft=python sts=4 ts=4 sw=4 et:
"""
The maths module provides higher-level interfaces to some of the operations
that can be performed with the fslmaths command-line program.
"""
import os
import numpy as np

from ..base import TraitedSpec, File, traits, InputMultiPath, isdefined
from .base import FSLCommand, FSLCommandInputSpec


class MathsInput(FSLCommandInputSpec):

    in_file = File(
        position=2, argstr="%s", exists=True, mandatory=True, desc="image to operate on"
    )
    out_file = File(
        genfile=True, position=-2, argstr="%s", desc="image to write", hash_files=False
    )
    _dtypes = ["float", "char", "int", "short", "double", "input"]
    internal_datatype = traits.Enum(
        *_dtypes,
        position=1,
        argstr="-dt %s",
        desc=("datatype to use for calculations " "(default is float)")
    )
    output_datatype = traits.Enum(
        *_dtypes,
        position=-1,
        argstr="-odt %s",
        desc=("datatype to use for output (default " "uses input type)")
    )

    nan2zeros = traits.Bool(
        position=3, argstr="-nan", desc="change NaNs to zeros before doing anything"
    )


class MathsOutput(TraitedSpec):

    out_file = File(exists=True, desc="image written after calculations")


class MathsCommand(FSLCommand):

    _cmd = "fslmaths"
    input_spec = MathsInput
    output_spec = MathsOutput
    _suffix = "_maths"

    def _list_outputs(self):
        outputs = self.output_spec().get()
        outputs["out_file"] = self.inputs.out_file
        if not isdefined(self.inputs.out_file):
            outputs["out_file"] = self._gen_fname(
                self.inputs.in_file, suffix=self._suffix
            )
        outputs["out_file"] = os.path.abspath(outputs["out_file"])
        return outputs

    def _gen_filename(self, name):
        if name == "out_file":
            return self._list_outputs()["out_file"]
        return None


class ChangeDataTypeInput(MathsInput):

    _dtypes = ["float", "char", "int", "short", "double", "input"]
    output_datatype = traits.Enum(
        *_dtypes, position=-1, argstr="-odt %s", mandatory=True, desc="output data type"
    )


class ChangeDataType(MathsCommand):
    """Use fslmaths to change the datatype of an image."""

    input_spec = ChangeDataTypeInput
    _suffix = "_chdt"


class ThresholdInputSpec(MathsInput):

    thresh = traits.Float(
        mandatory=True, position=4, argstr="%s", desc="threshold value"
    )
    direction = traits.Enum(
        "below",
        "above",
        usedefault=True,
        desc="zero-out either below or above thresh value",
    )
    use_robust_range = traits.Bool(
        desc="interpret thresh as percentage (0-100) of robust range"
    )
    use_nonzero_voxels = traits.Bool(
        desc="use nonzero voxels to calculate robust range",
        requires=["use_robust_range"],
    )


class Threshold(MathsCommand):
    """Use fslmaths to apply a threshold to an image in a variety of ways."""

    input_spec = ThresholdInputSpec
    _suffix = "_thresh"

    def _format_arg(self, name, spec, value):
        if name == "thresh":
            arg = "-"
            _si = self.inputs
            if self.inputs.direction == "above":
                arg += "u"
            arg += "thr"
            if isdefined(_si.use_robust_range) and _si.use_robust_range:
                if isdefined(_si.use_nonzero_voxels) and _si.use_nonzero_voxels:
                    arg += "P"
                else:
                    arg += "p"
            arg += " %.10f" % value
            return arg
        return super(Threshold, self)._format_arg(name, spec, value)


class StdImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sstd",
        position=4,
        desc="dimension to standard deviate across",
    )


class StdImage(MathsCommand):
    """Use fslmaths to generate a standard deviation in an image across a given
    dimension.
    """

    input_spec = StdImageInput
    _suffix = "_std"


class MeanImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smean",
        position=4,
        desc="dimension to mean across",
    )


class MeanImage(MathsCommand):
    """Use fslmaths to generate a mean image across a given dimension."""

    input_spec = MeanImageInput
    _suffix = "_mean"


class MaxImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smax",
        position=4,
        desc="dimension to max across",
    )


class MaxImage(MathsCommand):
    """Use fslmaths to generate a max image across a given dimension.

    Examples
    --------
    >>> from nipype.interfaces.fsl.maths import MaxImage
    >>> maxer = MaxImage()
    >>> maxer.inputs.in_file = "functional.nii"  # doctest: +SKIP
    >>> maxer.dimension = "T"
    >>> maxer.cmdline  # doctest: +SKIP
    'fslmaths functional.nii -Tmax functional_max.nii'

    """

    input_spec = MaxImageInput
    _suffix = "_max"


class PercentileImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sperc",
        position=4,
        desc="dimension to percentile across",
    )
    perc = traits.Range(
        low=0,
        high=100,
        argstr="%f",
        position=5,
        desc=("nth percentile (0-100) of FULL RANGE " "across dimension"),
    )


class PercentileImage(MathsCommand):
    """Use fslmaths to generate a percentile image across a given dimension.

    Examples
    --------
    >>> from nipype.interfaces.fsl.maths import MaxImage
    >>> percer = PercentileImage()
    >>> percer.inputs.in_file = "functional.nii"  # doctest: +SKIP
    >>> percer.dimension = "T"
    >>> percer.perc = 90
    >>> percer.cmdline  # doctest: +SKIP
    'fslmaths functional.nii -Tperc 90 functional_perc.nii'

    """

    input_spec = PercentileImageInput
    _suffix = "_perc"


class MaxnImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smaxn",
        position=4,
        desc="dimension to index max across",
    )


class MaxnImage(MathsCommand):
    """Use fslmaths to generate an image of index of max across
    a given dimension.

    """

    input_spec = MaxnImageInput
    _suffix = "_maxn"


class MinImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smin",
        position=4,
        desc="dimension to min across",
    )


class MinImage(MathsCommand):
    """Use fslmaths to generate a minimum image across a given dimension."""

    input_spec = MinImageInput
    _suffix = "_min"


class MedianImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smedian",
        position=4,
        desc="dimension to median across",
    )


class MedianImage(MathsCommand):
    """Use fslmaths to generate a median image across a given dimension."""

    input_spec = MedianImageInput
    _suffix = "_median"


class AR1ImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sar1",
        position=4,
        desc=("dimension to find AR(1) coefficient" "across"),
    )


class AR1Image(MathsCommand):
    """Use fslmaths to generate an AR1 coefficient image across a
    given dimension. (Should use -odt float and probably demean first)

    """

    input_spec = AR1ImageInput
    _suffix = "_ar1"


class IsotropicSmoothInput(MathsInput):

    fwhm = traits.Float(
        mandatory=True,
        xor=["sigma"],
        position=4,
        argstr="-s %.5f",
        desc="fwhm of smoothing kernel [mm]",
    )
    sigma = traits.Float(
        mandatory=True,
        xor=["fwhm"],
        position=4,
        argstr="-s %.5f",
        desc="sigma of smoothing kernel [mm]",
    )


class IsotropicSmooth(MathsCommand):
    """Use fslmaths to spatially smooth an image with a gaussian kernel."""

    input_spec = IsotropicSmoothInput
    _suffix = "_smooth"

    def _format_arg(self, name, spec, value):
        if name == "fwhm":
            sigma = float(value) / np.sqrt(8 * np.log(2))
            return spec.argstr % sigma
        return super(IsotropicSmooth, self)._format_arg(name, spec, value)


class ApplyMaskInput(MathsInput):

    mask_file = File(
        exists=True,
        mandatory=True,
        argstr="-mas %s",
        position=4,
        desc="binary image defining mask space",
    )


class ApplyMask(MathsCommand):
    """Use fslmaths to apply a binary mask to another image."""

    input_spec = ApplyMaskInput
    _suffix = "_masked"


class KernelInput(MathsInput):

    kernel_shape = traits.Enum(
        "3D",
        "2D",
        "box",
        "boxv",
        "gauss",
        "sphere",
        "file",
        argstr="-kernel %s",
        position=4,
        desc="kernel shape to use",
    )
    kernel_size = traits.Float(
        argstr="%.4f",
        position=5,
        xor=["kernel_file"],
        desc=(
            "kernel size - voxels for box/boxv, mm " "for sphere, mm sigma for gauss"
        ),
    )
    kernel_file = File(
        exists=True,
        argstr="%s",
        position=5,
        xor=["kernel_size"],
        desc="use external file for kernel",
    )


class DilateInput(KernelInput):

    operation = traits.Enum(
        "mean",
        "modal",
        "max",
        argstr="-dil%s",
        position=6,
        mandatory=True,
        desc="filtering operation to perfoem in dilation",
    )


class DilateImage(MathsCommand):
    """Use fslmaths to perform a spatial dilation of an image."""

    input_spec = DilateInput
    _suffix = "_dil"

    def _format_arg(self, name, spec, value):
        if name == "operation":
            return spec.argstr % dict(mean="M", modal="D", max="F")[value]
        return super(DilateImage, self)._format_arg(name, spec, value)


class ErodeInput(KernelInput):

    minimum_filter = traits.Bool(
        argstr="%s",
        position=6,
        usedefault=True,
        default_value=False,
        desc=("if true, minimum filter rather than " "erosion by zeroing-out"),
    )


class ErodeImage(MathsCommand):
    """Use fslmaths to perform a spatial erosion of an image."""

    input_spec = ErodeInput
    _suffix = "_ero"

    def _format_arg(self, name, spec, value):
        if name == "minimum_filter":
            if value:
                return "-eroF"
            return "-ero"
        return super(ErodeImage, self)._format_arg(name, spec, value)


class SpatialFilterInput(KernelInput):

    operation = traits.Enum(
        "mean",
        "median",
        "meanu",
        argstr="-f%s",
        position=6,
        mandatory=True,
        desc="operation to filter with",
    )


class SpatialFilter(MathsCommand):
    """Use fslmaths to spatially filter an image."""

    input_spec = SpatialFilterInput
    _suffix = "_filt"


class UnaryMathsInput(MathsInput):

    operation = traits.Enum(
        "exp",
        "log",
        "sin",
        "cos",
        "tan",
        "asin",
        "acos",
        "atan",
        "sqr",
        "sqrt",
        "recip",
        "abs",
        "bin",
        "binv",
        "fillh",
        "fillh26",
        "index",
        "edge",
        "nan",
        "nanm",
        "rand",
        "randn",
        "range",
        argstr="-%s",
        position=4,
        mandatory=True,
        desc="operation to perform",
    )


class UnaryMaths(MathsCommand):
    """Use fslmaths to perorm a variety of mathematical operations on an image."""

    input_spec = UnaryMathsInput

    def _list_outputs(self):
        self._suffix = "_" + self.inputs.operation
        return super(UnaryMaths, self)._list_outputs()


class BinaryMathsInput(MathsInput):

    operation = traits.Enum(
        "add",
        "sub",
        "mul",
        "div",
        "rem",
        "max",
        "min",
        mandatory=True,
        argstr="-%s",
        position=4,
        desc="operation to perform",
    )
    operand_file = File(
        exists=True,
        argstr="%s",
        mandatory=True,
        position=5,
        xor=["operand_value"],
        desc="second image to perform operation with",
    )
    operand_value = traits.Float(
        argstr="%.8f",
        mandatory=True,
        position=5,
        xor=["operand_file"],
        desc="value to perform operation with",
    )


class BinaryMaths(MathsCommand):
    """Use fslmaths to perform mathematical operations using a second image or
    a numeric value.

    """

    input_spec = BinaryMathsInput


class MultiImageMathsInput(MathsInput):

    op_string = traits.String(
        position=4,
        argstr="%s",
        mandatory=True,
        desc=("python formatted string of operations " "to perform"),
    )
    operand_files = InputMultiPath(
        File(exists=True),
        mandatory=True,
        desc=("list of file names to plug into op " "string"),
    )


class MultiImageMaths(MathsCommand):
    """Use fslmaths to perform a sequence of mathematical operations.

    Examples
    --------
    >>> from nipype.interfaces.fsl import MultiImageMaths
    >>> maths = MultiImageMaths()
    >>> maths.inputs.in_file = "functional.nii"
    >>> maths.inputs.op_string = "-add %s -mul -1 -div %s"
    >>> maths.inputs.operand_files = ["functional2.nii", "functional3.nii"]
    >>> maths.inputs.out_file = "functional4.nii"
    >>> maths.cmdline
    'fslmaths functional.nii -add functional2.nii -mul -1 -div functional3.nii functional4.nii'

    """

    input_spec = MultiImageMathsInput

    def _format_arg(self, name, spec, value):
        if name == "op_string":
            return value % tuple(self.inputs.operand_files)
        return super(MultiImageMaths, self)._format_arg(name, spec, value)


class TemporalFilterInput(MathsInput):

    lowpass_sigma = traits.Float(
        -1,
        argstr="%.6f",
        position=5,
        usedefault=True,
        desc="lowpass filter sigma (in volumes)",
    )
    highpass_sigma = traits.Float(
        -1,
        argstr="-bptf %.6f",
        position=4,
        usedefault=True,
        desc="highpass filter sigma (in volumes)",
    )


class TemporalFilter(MathsCommand):
    """Use fslmaths to apply a low, high, or bandpass temporal filter to a
    timeseries.

    """

    input_spec = TemporalFilterInput
    _suffix = "_filt"

nipype/interfaces/fsl/maths.py
# -*- coding: utf-8 -*-
# emacs: -*- mode: python; py-indent-offset: 4; indent-tabs-mode: nil -*-
# vi: set ft=python sts=4 ts=4 sw=4 et:
"""
The maths module provides higher-level interfaces to some of the operations
that can be performed with the fslmaths command-line program.
"""
import os
import numpy as np

from ..base import TraitedSpec, File, traits, InputMultiPath, isdefined
from .base import FSLCommand, FSLCommandInputSpec


class MathsInput(FSLCommandInputSpec):

    in_file = File(
        position=2, argstr="%s", exists=True, mandatory=True, desc="image to operate on"
    )
    out_file = File(
        genfile=True, position=-2, argstr="%s", desc="image to write", hash_files=False
    )
    _dtypes = ["float", "char", "int", "short", "double", "input"]
    internal_datatype = traits.Enum(
        *_dtypes,
        position=1,
        argstr="-dt %s",
        desc=("datatype to use for calculations " "(default is float)")
    )
    output_datatype = traits.Enum(
        *_dtypes,
        position=-1,
        argstr="-odt %s",
        desc=("datatype to use for output (default " "uses input type)")
    )

    nan2zeros = traits.Bool(
        position=3, argstr="-nan", desc="change NaNs to zeros before doing anything"
    )


class MathsOutput(TraitedSpec):

    out_file = File(desc="image written after calculations")


class MathsCommand(FSLCommand):

    _cmd = "fslmaths"
    input_spec = MathsInput
    output_spec = MathsOutput
    _suffix = "_maths"

    def _list_outputs(self):
        outputs = self.output_spec().get()
        outputs["out_file"] = self.inputs.out_file
        if not isdefined(self.inputs.out_file):
            outputs["out_file"] = self._gen_fname(
                self.inputs.in_file, suffix=self._suffix
            )
        outputs["out_file"] = os.path.abspath(outputs["out_file"])
        return outputs

    def _gen_filename(self, name):
        if name == "out_file":
            return self._list_outputs()["out_file"]
        return None


class ChangeDataTypeInput(MathsInput):

    _dtypes = ["float", "char", "int", "short", "double", "input"]
    output_datatype = traits.Enum(
        *_dtypes, position=-1, argstr="-odt %s", mandatory=True, desc="output data type"
    )


class ChangeDataType(MathsCommand):
    """Use fslmaths to change the datatype of an image."""

    input_spec = ChangeDataTypeInput
    _suffix = "_chdt"


class ThresholdInputSpec(MathsInput):

    thresh = traits.Float(
        mandatory=True, position=4, argstr="%s", desc="threshold value"
    )
    direction = traits.Enum(
        "below",
        "above",
        usedefault=True,
        desc="zero-out either below or above thresh value",
    )
    use_robust_range = traits.Bool(
        desc="interpret thresh as percentage (0-100) of robust range"
    )
    use_nonzero_voxels = traits.Bool(
        desc="use nonzero voxels to calculate robust range",
        requires=["use_robust_range"],
    )


class Threshold(MathsCommand):
    """Use fslmaths to apply a threshold to an image in a variety of ways."""

    input_spec = ThresholdInputSpec
    _suffix = "_thresh"

    def _format_arg(self, name, spec, value):
        if name == "thresh":
            arg = "-"
            _si = self.inputs
            if self.inputs.direction == "above":
                arg += "u"
            arg += "thr"
            if isdefined(_si.use_robust_range) and _si.use_robust_range:
                if isdefined(_si.use_nonzero_voxels) and _si.use_nonzero_voxels:
                    arg += "P"
                else:
                    arg += "p"
            arg += " %.10f" % value
            return arg
        return super(Threshold, self)._format_arg(name, spec, value)


class StdImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sstd",
        position=4,
        desc="dimension to standard deviate across",
    )


class StdImage(MathsCommand):
    """Use fslmaths to generate a standard deviation in an image across a given
    dimension.
    """

    input_spec = StdImageInput
    _suffix = "_std"


class MeanImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smean",
        position=4,
        desc="dimension to mean across",
    )


class MeanImage(MathsCommand):
    """Use fslmaths to generate a mean image across a given dimension."""

    input_spec = MeanImageInput
    _suffix = "_mean"


class MaxImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smax",
        position=4,
        desc="dimension to max across",
    )


class MaxImage(MathsCommand):
    """Use fslmaths to generate a max image across a given dimension.

    Examples
    --------
    >>> from nipype.interfaces.fsl.maths import MaxImage
    >>> maxer = MaxImage()
    >>> maxer.inputs.in_file = "functional.nii"  # doctest: +SKIP
    >>> maxer.dimension = "T"
    >>> maxer.cmdline  # doctest: +SKIP
    'fslmaths functional.nii -Tmax functional_max.nii'

    """

    input_spec = MaxImageInput
    _suffix = "_max"


class PercentileImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sperc",
        position=4,
        desc="dimension to percentile across",
    )
    perc = traits.Range(
        low=0,
        high=100,
        argstr="%f",
        position=5,
        desc=("nth percentile (0-100) of FULL RANGE " "across dimension"),
    )


class PercentileImage(MathsCommand):
    """Use fslmaths to generate a percentile image across a given dimension.

    Examples
    --------
    >>> from nipype.interfaces.fsl.maths import MaxImage
    >>> percer = PercentileImage()
    >>> percer.inputs.in_file = "functional.nii"  # doctest: +SKIP
    >>> percer.dimension = "T"
    >>> percer.perc = 90
    >>> percer.cmdline  # doctest: +SKIP
    'fslmaths functional.nii -Tperc 90 functional_perc.nii'

    """

    input_spec = PercentileImageInput
    _suffix = "_perc"


class MaxnImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smaxn",
        position=4,
        desc="dimension to index max across",
    )


class MaxnImage(MathsCommand):
    """Use fslmaths to generate an image of index of max across
    a given dimension.

    """

    input_spec = MaxnImageInput
    _suffix = "_maxn"


class MinImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smin",
        position=4,
        desc="dimension to min across",
    )


class MinImage(MathsCommand):
    """Use fslmaths to generate a minimum image across a given dimension."""

    input_spec = MinImageInput
    _suffix = "_min"


class MedianImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%smedian",
        position=4,
        desc="dimension to median across",
    )


class MedianImage(MathsCommand):
    """Use fslmaths to generate a median image across a given dimension."""

    input_spec = MedianImageInput
    _suffix = "_median"


class AR1ImageInput(MathsInput):

    dimension = traits.Enum(
        "T",
        "X",
        "Y",
        "Z",
        usedefault=True,
        argstr="-%sar1",
        position=4,
        desc=("dimension to find AR(1) coefficient" "across"),
    )


class AR1Image(MathsCommand):
    """Use fslmaths to generate an AR1 coefficient image across a
    given dimension. (Should use -odt float and probably demean first)

    """

    input_spec = AR1ImageInput
    _suffix = "_ar1"


class IsotropicSmoothInput(MathsInput):

    fwhm = traits.Float(
        mandatory=True,
        xor=["sigma"],
        position=4,
        argstr="-s %.5f",
        desc="fwhm of smoothing kernel [mm]",
    )
    sigma = traits.Float(
        mandatory=True,
        xor=["fwhm"],
        position=4,
        argstr="-s %.5f",
        desc="sigma of smoothing kernel [mm]",
    )


class IsotropicSmooth(MathsCommand):
    """Use fslmaths to spatially smooth an image with a gaussian kernel."""

    input_spec = IsotropicSmoothInput
    _suffix = "_smooth"

    def _format_arg(self, name, spec, value):
        if name == "fwhm":
            sigma = float(value) / np.sqrt(8 * np.log(2))
            return spec.argstr % sigma
        return super(IsotropicSmooth, self)._format_arg(name, spec, value)


class ApplyMaskInput(MathsInput):

    mask_file = File(
        exists=True,
        mandatory=True,
        argstr="-mas %s",
        position=4,
        desc="binary image defining mask space",
    )


class ApplyMask(MathsCommand):
    """Use fslmaths to apply a binary mask to another image."""

    input_spec = ApplyMaskInput
    _suffix = "_masked"


class KernelInput(MathsInput):

    kernel_shape = traits.Enum(
        "3D",
        "2D",
        "box",
        "boxv",
        "gauss",
        "sphere",
        "file",
        argstr="-kernel %s",
        position=4,
        desc="kernel shape to use",
    )
    kernel_size = traits.Float(
        argstr="%.4f",
        position=5,
        xor=["kernel_file"],
        desc=(
            "kernel size - voxels for box/boxv, mm " "for sphere, mm sigma for gauss"
        ),
    )
    kernel_file = File(
        exists=True,
        argstr="%s",
        position=5,
        xor=["kernel_size"],
        desc="use external file for kernel",
    )


class DilateInput(KernelInput):

    operation = traits.Enum(
        "mean",
        "modal",
        "max",
        argstr="-dil%s",
        position=6,
        mandatory=True,
        desc="filtering operation to perfoem in dilation",
    )


class DilateImage(MathsCommand):
    """Use fslmaths to perform a spatial dilation of an image."""

    input_spec = DilateInput
    _suffix = "_dil"

    def _format_arg(self, name, spec, value):
        if name == "operation":
            return spec.argstr % dict(mean="M", modal="D", max="F")[value]
        return super(DilateImage, self)._format_arg(name, spec, value)


class ErodeInput(KernelInput):

    minimum_filter = traits.Bool(
        argstr="%s",
        position=6,
        usedefault=True,
        default_value=False,
        desc=("if true, minimum filter rather than " "erosion by zeroing-out"),
    )


class ErodeImage(MathsCommand):
    """Use fslmaths to perform a spatial erosion of an image."""

    input_spec = ErodeInput
    _suffix = "_ero"

    def _format_arg(self, name, spec, value):
        if name == "minimum_filter":
            if value:
                return "-eroF"
            return "-ero"
        return super(ErodeImage, self)._format_arg(name, spec, value)


class SpatialFilterInput(KernelInput):

    operation = traits.Enum(
        "mean",
        "median",
        "meanu",
        argstr="-f%s",
        position=6,
        mandatory=True,
        desc="operation to filter with",
    )


class SpatialFilter(MathsCommand):
    """Use fslmaths to spatially filter an image."""

    input_spec = SpatialFilterInput
    _suffix = "_filt"


class UnaryMathsInput(MathsInput):

    operation = traits.Enum(
        "exp",
        "log",
        "sin",
        "cos",
        "tan",
        "asin",
        "acos",
        "atan",
        "sqr",
        "sqrt",
        "recip",
        "abs",
        "bin",
        "binv",
        "fillh",
        "fillh26",
        "index",
        "edge",
        "nan",
        "nanm",
        "rand",
        "randn",
        "range",
        argstr="-%s",
        position=4,
        mandatory=True,
        desc="operation to perform",
    )


class UnaryMaths(MathsCommand):
    """Use fslmaths to perorm a variety of mathematical operations on an image."""

    input_spec = UnaryMathsInput

    def _list_outputs(self):
        self._suffix = "_" + self.inputs.operation
        return super(UnaryMaths, self)._list_outputs()


class BinaryMathsInput(MathsInput):

    operation = traits.Enum(
        "add",
        "sub",
        "mul",
        "div",
        "rem",
        "max",
        "min",
        mandatory=True,
        argstr="-%s",
        position=4,
        desc="operation to perform",
    )
    operand_file = File(
        exists=True,
        argstr="%s",
        mandatory=True,
        position=5,
        xor=["operand_value"],
        desc="second image to perform operation with",
    )
    operand_value = traits.Float(
        argstr="%.8f",
        mandatory=True,
        position=5,
        xor=["operand_file"],
        desc="value to perform operation with",
    )


class BinaryMaths(MathsCommand):
    """Use fslmaths to perform mathematical operations using a second image or
    a numeric value.

    """

    input_spec = BinaryMathsInput


class MultiImageMathsInput(MathsInput):

    op_string = traits.String(
        position=4,
        argstr="%s",
        mandatory=True,
        desc=("python formatted string of operations " "to perform"),
    )
    operand_files = InputMultiPath(
        File(exists=True),
        mandatory=True,
        desc=("list of file names to plug into op " "string"),
    )


class MultiImageMaths(MathsCommand):
    """Use fslmaths to perform a sequence of mathematical operations.

    Examples
    --------
    >>> from nipype.interfaces.fsl import MultiImageMaths
    >>> maths = MultiImageMaths()
    >>> maths.inputs.in_file = "functional.nii"
    >>> maths.inputs.op_string = "-add %s -mul -1 -div %s"
    >>> maths.inputs.operand_files = ["functional2.nii", "functional3.nii"]
    >>> maths.inputs.out_file = "functional4.nii"
    >>> maths.cmdline
    'fslmaths functional.nii -add functional2.nii -mul -1 -div functional3.nii functional4.nii'

    """

    input_spec = MultiImageMathsInput

    def _format_arg(self, name, spec, value):
        if name == "op_string":
            return value % tuple(self.inputs.operand_files)
        return super(MultiImageMaths, self)._format_arg(name, spec, value)


class TemporalFilterInput(MathsInput):

    lowpass_sigma = traits.Float(
        -1,
        argstr="%.6f",
        position=5,
        usedefault=True,
        desc="lowpass filter sigma (in volumes)",
    )
    highpass_sigma = traits.Float(
        -1,
        argstr="-bptf %.6f",
        position=4,
        usedefault=True,
        desc="highpass filter sigma (in volumes)",
    )


class TemporalFilter(MathsCommand):
    """Use fslmaths to apply a low, high, or bandpass temporal filter to a
    timeseries.

    """

    input_spec = TemporalFilterInput
    _suffix = "_filt"

nipype/interfaces/fsl/maths.py
diff --git a/nipype/interfaces/fsl/maths.py b/nipype/interfaces/fsl/maths.py
index 9e05b4d102..f3276024b7 100644
--- a/nipype/interfaces/fsl/maths.py
+++ b/nipype/interfaces/fsl/maths.py
@@ -41,7 +41,7 @@ class MathsInput(FSLCommandInputSpec):
 
 class MathsOutput(TraitedSpec):
 
-    out_file = File(exists=True, desc="image written after calculations")
+    out_file = File(desc="image written after calculations")
 
 
 class MathsCommand(FSLCommand):

MathsCommand().inputs.out_file has to exist
When setting `MathsCommand().inputs.out_file` argument, a Trait error is thrown because of the `exists=True`:

https://github.com/nipy/nipype/blob/6a7837c0994367a5f34bb576bb0a97ec70669b8f/nipype/interfaces/fsl/maths.py#L44

I think this doesn't make any sense, because `out_file` is to be created by `MathsCommand()`.
In my case, I just want to get rid of SPM nan's in an .nii file, but I also don't want fsl_maths to append a suffix to the filename - this is why I also provide `out_file` to `MathsCommand().inputs`.
A short example:
```
nan2zero = pe.MapNode(interface=MathsCommand(), name='nan2zero', iterfield=['in_file', 'out_file'])
nan2zero.inputs.nan2zeros = True

```
