# Source code for drizzlepac.createMedian

    """
    Create a median image from the singly drizzled images.

    :Authors: Warren Hack, Mihai Cara

    :License: :doc:`LICENSE`

    """

    # Import external packages
    from __future__ import (absolute_import, division, unicode_literals,
                            print_function)

    import os
    import sys
    import math
    import numpy as np
    from astropy.io import fits

    from stsci.imagestats import ImageStats
    from stsci.image import numcombine
    from stsci.tools import iterfile, teal, logutil

    from . import imageObject
    from . import util
    from .minmed import min_med
    from . import processInput
    from .adrizzle import _single_step_num_

    from .version import *

    # look in drizzlepac for createMedian.cfg:
    __taskname__ = "drizzlepac.createMedian"
    _step_num_ = 4  # this relates directly to the syntax in the cfg file

    BUFSIZE = 1024*1024   # 1MB cache size

    log = logutil.create_logger(__name__, level=logutil.logging.NOTSET)

    # this is the user access function
    def median(input=None, configObj=None, editpars=False, **inputDict):
        """
        Create a median image from the seperately drizzled images.
        """
        if input is not None:
            inputDict["input"] = input
        else:
            raise ValueError("Please supply an input image")

        configObj = util.getDefaultConfigObj(__taskname__, configObj, inputDict,
                                             loadOnly=(not editpars))
        if configObj is None:
            return

        if not editpars:
            run(configObj)

    # this is the function that will be called from TEAL
    def run(configObj):
        imgObjList, outwcs = processInput.setCommonInput(
            configObj,
            createOutwcs=False
        )  # outwcs is not needed here
        createMedian(imgObjList, configObj)

    # ###################################################
    # ## Top-level interface from inside AstroDrizzle  ##
    # ###################################################
    def createMedian(imgObjList, configObj, procSteps=None):
        """ Top-level interface to createMedian step called from top-level
        AstroDrizzle.

        This function parses the input parameters then calls the `_median()`
        function to median-combine the input images into a single image.

        """
        if imgObjList is None:
            msg = "Please provide a list of imageObjects to the median step"
            print(msg, file=sys.stderr)
            raise ValueError(msg)

        if procSteps is not None:
            procSteps.addStep('Create Median')

        step_name = util.getSectionName(configObj, _step_num_)
        if not configObj[step_name]['median']:
            log.info('Median combination step not performed.')
            return

        paramDict = configObj[step_name]
        paramDict['proc_unit'] = configObj['proc_unit']

        # include whether or not compression was performed
        driz_sep_name = util.getSectionName(configObj, _single_step_num_)
        driz_sep_paramDict = configObj[driz_sep_name]
        paramDict['compress'] = driz_sep_paramDict['driz_sep_compress']

        log.info('USER INPUT PARAMETERS for Create Median Step:')
        util.printParams(paramDict, log=log)

        _median(imgObjList, paramDict)

        if procSteps is not None:
            procSteps.endStep('Create Median')

    # this is the internal function, the user called function is below
    def _median(imageObjectList, paramDict):
        """Create a median image from the list of image Objects
           that has been given.
        """
        newmasks = paramDict['median_newmasks']
        comb_type = paramDict['combine_type'].lower()
        nlow = paramDict['combine_nlow']
        nhigh = paramDict['combine_nhigh']
        grow = paramDict['combine_grow'] if 'minmed' in comb_type else 0
        maskpt = paramDict['combine_maskpt']
        proc_units = paramDict['proc_unit']
        compress = paramDict['compress']
        bufsizeMB = paramDict['combine_bufsize']

        sigma = paramDict["combine_nsigma"]
        sigmaSplit = sigma.split()
        nsigma1 = float(sigmaSplit[0])
        nsigma2 = float(sigmaSplit[1])

        if paramDict['combine_lthresh'] is None:
            lthresh = None
        else:
            lthresh = float(paramDict['combine_lthresh'])

        if paramDict['combine_hthresh'] is None:
            hthresh = None
        else:
            hthresh = float(paramDict['combine_hthresh'])

        # the name of the output median file isdefined in the output wcs object and
        # stuck in the image.outputValues["outMedian"] dict of every imageObject
        medianfile = imageObjectList[0].outputNames["outMedian"]

        # Build combined array from single drizzled images.

        # Start by removing any previous products...
        if os.access(medianfile, os.F_OK):
            os.remove(medianfile)

        # Define lists for instrument specific parameters, these should be in
        # the image objects need to be passed to the minmed routine
        readnoiseList = []
        exposureTimeList = []
        backgroundValueList = []  # list of  MDRIZSKY *platescale values
        singleDrizList = []  # these are the input images
        singleWeightList = []  # pointers to the data arrays
        wht_mean = []  # Compute the mean value of each wht image

        single_hdr = None
        virtual = None

        # for each image object
        for image in imageObjectList:
            if virtual is None:
                virtual = image.inmemory

            det_gain = image.getGain(1)
            img_exptime = image._image['sci', 1]._exptime
            native_units = image.native_units
            native_units_lc = native_units.lower()

            if proc_units.lower() == 'native':
                if native_units_lc not in ['counts', 'electrons', 'counts/s',
                                           'electrons/s']:
                    raise ValueError("Unexpected native units: '{}'"
                                     .format(native_units))

                if lthresh is not None:
                    if native_units_lc.startswith('counts'):
                        lthresh *= det_gain
                    if native_units_lc.endswith('/s'):
                        lthresh *= img_exptime

                if hthresh is not None:
                    if native_units_lc.startswith('counts'):
                        hthresh *= det_gain
                    if native_units_lc.endswith('/s'):
                        hthresh *= img_exptime

            singleDriz = image.getOutputName("outSingle")
            singleDriz_name = image.outputNames['outSingle']
            singleWeight = image.getOutputName("outSWeight")
            singleWeight_name = image.outputNames['outSWeight']

            # If compression was used, reference ext=1 as CompImageHDU only writes
            # out MEF files, not simple FITS.
            if compress:
                wcs_ext = '[1]'
                wcs_extnum = 1
            else:
                wcs_ext = '[0]'
                wcs_extnum = 0

            if not virtual:
                if isinstance(singleDriz, str):
                    iter_singleDriz = singleDriz + wcs_ext
                    iter_singleWeight = singleWeight + wcs_ext
                else:
                    iter_singleDriz = singleDriz[wcs_extnum]
                    iter_singleWeight = singleWeight[wcs_extnum]
            else:
                iter_singleDriz = singleDriz_name + wcs_ext
                iter_singleWeight = singleWeight_name + wcs_ext

            # read in WCS from first single drizzle image to use as WCS for
            # median image
            if single_hdr is None:
                if virtual:
                    single_hdr = singleDriz[wcs_extnum].header
                else:
                    single_hdr = fits.getheader(singleDriz_name, ext=wcs_extnum,
                                                memmap=False)

            single_image = iterfile.IterFitsFile(iter_singleDriz)
            if virtual:
                single_image.handle = singleDriz
                single_image.inmemory = True

            singleDrizList.append(single_image)  # add to an array for bookkeeping

            # If it exists, extract the corresponding weight images
            if (not virtual and os.access(singleWeight, os.F_OK)) or (
                    virtual and singleWeight):
                weight_file = iterfile.IterFitsFile(iter_singleWeight)
                if virtual:
                    weight_file.handle = singleWeight
                    weight_file.inmemory = True

                singleWeightList.append(weight_file)
                try:
                    tmp_mean_value = ImageStats(weight_file.data, lower=1e-8,
                                                fields="mean", nclip=0).mean
                except ValueError:
                    tmp_mean_value = 0.0
                wht_mean.append(tmp_mean_value * maskpt)

                # Extract instrument specific parameters and place in lists

                # If an image has zero exposure time we will
                # redefine that value as '1'.  Although this will cause inaccurate
                # scaling of the data to occur in the 'minmed' combination
                # algorith, this is a necessary evil since it avoids divide by
                # zero exceptions.  It is more important that the divide by zero
                # exceptions not cause AstroDrizzle to crash in the pipeline than
                # it is to raise an exception for this obviously bad data even
                # though this is not the type of data you would wish to process
                # with AstroDrizzle.
                #
                # Get the exposure time from the InputImage object
                #
                # MRD 19-May-2011
                # Changed exposureTimeList to take exposure time from img_exptime
                # variable instead of hte image._exptime attribute, since
                # image._exptime was just giving 1.
                #
                exposureTimeList.append(img_exptime)

                # Use only "commanded" chips to extract subtractedSky and rdnoise:
                rdnoise = 0.0
                nchips = 0
                bsky = None  # minimum sky across **used** chips

                for chip in image.returnAllChips(extname=image.scienceExt):
                    # compute sky value as sky/pixel using the single_drz
                    # pixel scale:
                    if bsky is None or bsky > chip.subtractedSky:
                        bsky = chip.subtractedSky * chip._conversionFactor

                    # Extract the readnoise value for the chip
                    rdnoise += chip._rdnoise**2
                    nchips += 1

                if bsky is None:
                    bsky = 0.0

                if nchips > 0:
                    rdnoise = math.sqrt(rdnoise/nchips)

                backgroundValueList.append(bsky)
                readnoiseList.append(rdnoise)

                print("reference sky value for image '{}' is {}"
                      .format(image._filename, backgroundValueList[-1]))
            #
            # END Loop over input image list
            #

        # create an array for the median output image, use the size of the first
        # image in the list. Store other useful image characteristics:
        single_driz_data = singleDrizList[0].data
        data_item_size = single_driz_data.itemsize
        single_data_dtype = single_driz_data.dtype
        imrows, imcols = single_driz_data.shape

        medianImageArray = np.zeros_like(single_driz_data)

        del single_driz_data

        if comb_type == "minmed" and not newmasks:
            # Issue a warning if minmed is being run with newmasks turned off.
            print('\nWARNING: Creating median image without the application of '
                  'bad pixel masks!\n')

        # The overlap value needs to be set to 2*grow in order to
        # avoid edge effects when scrolling down the image, and to
        # insure that the last section returned from the iterator
        # has enough rows to span the kernel used in the boxcar method
        # within minmed.
        overlap = 2 * grow
        buffsize = BUFSIZE if bufsizeMB is None else (BUFSIZE * bufsizeMB)
        section_nrows = min(imrows, int(buffsize / (imcols * data_item_size)))

        if section_nrows == 0:
            buffsize = imcols * data_item_size
            print("WARNING: Buffer size is too small to hold a single row.\n"
                  "         Buffer size size will be increased to minimal "
                  "required: {}MB".format(float(buffsize) / 1048576.0))
            section_nrows = 1

        if section_nrows < overlap + 1:
            new_grow = int((section_nrows - 1) / 2)
            if section_nrows == imrows:
                print("'grow' parameter is too large for actual image size. "
                      "Reducing 'grow' to {}".format(new_grow))
            else:
                print("'grow' parameter is too large for requested buffer size. "
                      "Reducing 'grow' to {}".format(new_grow))
            grow = new_grow
            overlap = 2 * grow

        nbr = section_nrows - overlap
        nsec = (imrows - overlap) // nbr
        if (imrows - overlap) % nbr > 0:
            nsec += 1

        for k in range(nsec):
            e1 = k * nbr
            e2 = e1 + section_nrows
            u1 = grow
            u2 = u1 + nbr

            if k == 0:  # first section
                u1 = 0

            if k == nsec - 1:  # last section
                e2 = min(e2, imrows)
                e1 = min(e1, e2 - overlap - 1)
                u2 = e2 - e1

            imdrizSectionsList = np.empty(
                (len(singleDrizList), e2 - e1, imcols),
                dtype=single_data_dtype
            )
            for i, w in enumerate(singleDrizList):
                imdrizSectionsList[i, :, :] = w[e1:e2]

            if singleWeightList:
                weightSectionsList = np.empty(
                    (len(singleWeightList), e2 - e1, imcols),
                    dtype=single_data_dtype
                )
                for i, w in enumerate(singleWeightList):
                    weightSectionsList[i, :, :] = w[e1:e2]
            else:
                weightSectionsList = None

            weight_mask_list = None

            if newmasks and weightSectionsList is not None:
                # Build new masks from single drizzled images.
                # Generate new pixel mask file for median step.
                # This mask will be created from the single-drizzled
                # weight image for this image.

                # The mean of the weight array will be computed and all
                # pixels with values less than 0.7 of the mean will be flagged
                # as bad in this mask. This mask will then be used when
                # creating the median image.
                # 0 means good, 1 means bad here...
                weight_mask_list = np.less(
                    weightSectionsList,
                    np.asarray(wht_mean)[:, None, None]
                ).astype(np.uint8)

            if 'minmed' in comb_type:  # Do MINMED
                # set up use of 'imedian'/'imean' in minmed algorithm
                fillval = comb_type.startswith('i')

                # Create the combined array object using the minmed algorithm
                result = min_med(
                    imdrizSectionsList,
                    weightSectionsList,
                    readnoiseList,
                    exposureTimeList,
                    backgroundValueList,
                    weight_masks=weight_mask_list,
                    combine_grow=grow,
                    combine_nsigma1=nsigma1,
                    combine_nsigma2=nsigma2,
                    fillval=fillval
                )

            else:  # DO NUMCOMBINE
                # Create the combined array object using the numcombine task
                result = numcombine.num_combine(
                    imdrizSectionsList,
                    masks=weight_mask_list,
                    combination_type=comb_type,
                    nlow=nlow,
                    nhigh=nhigh,
                    upper=hthresh,
                    lower=lthresh
                )

            # Write out the processed image sections to the final output array:
            medianImageArray[e1+u1:e1+u2, :] = result[u1:u2, :]

        # Write out the combined image
        # use the header from the first single drizzled image in the list
        pf = _writeImage(medianImageArray, inputHeader=single_hdr)

        if virtual:
            mediandict = {}
            mediandict[medianfile] = pf
            for img in imageObjectList:
                img.saveVirtualOutputs(mediandict)
        else:
            try:
                print("Saving output median image to: '{}'".format(medianfile))
                pf.writeto(medianfile)
            except IOError:
                msg = "Problem writing file '{}'".format(medianfile)
                print(msg)
                raise IOError(msg)

        # Always close any files opened to produce median image; namely,
        # single drizzle images and singly-drizzled weight images
        #
        for img in singleDrizList:
            if not virtual:
                img.close()

        # Close all singly drizzled weight images used to create median image.
        for img in singleWeightList:
            if not virtual:
                img.close()

    def _writeImage(dataArray=None, inputHeader=None):
        """ Writes out the result of the combination step.
            The header of the first 'outsingle' file in the
            association parlist is used as the header of the
            new image.

            Parameters
            ----------
            dataArray : arr
                Array of data to be written to a fits.PrimaryHDU object

            inputHeader : obj
                fits.header.Header object to use as basis for the PrimaryHDU header

        """
        prihdu = fits.PrimaryHDU(data=dataArray, header=inputHeader)
        pf = fits.HDUList()
        pf.append(prihdu)
        return pf

    def help(file=None):
        """
        Print out syntax help for running astrodrizzle

        Parameters
        ----------
        file : str (Default = None)
            If given, write out help to the filename specified by this parameter
            Any previously existing file with this name will be deleted before
            writing out the help.

        """
        helpstr = getHelpAsString(docstring=True, show_ver=True)
        if file is None:
            print(helpstr)
        else:
            if os.path.exists(file):
                os.remove(file)
            f = open(file, mode='w')
            f.write(helpstr)
            f.close()

    def getHelpAsString(docstring=False, show_ver=True):
        """
        return useful help from a file in the script directory called
        __taskname__.help

        """
        install_dir = os.path.dirname(__file__)
        taskname = util.base_taskname(__taskname__, __package__)
        htmlfile = os.path.join(install_dir, 'htmlhelp', taskname + '.html')
        helpfile = os.path.join(install_dir, taskname + '.help')

        if docstring or (not docstring and not os.path.exists(htmlfile)):
            if show_ver:
                helpString = os.linesep + \
                    ' '.join([__taskname__, 'Version', __version__,
                    ' updated on ', __version_date__]) + 2*os.linesep
            else:
                helpString = ''

            if os.path.exists(helpfile):
                helpString += teal.getHelpFileAsString(taskname, __file__)
            else:
                if __doc__ is not None:
                    helpString += __doc__ + os.linesep

        else:
            helpString = 'file://' + htmlfile

        return helpString

    median.__doc__ = getHelpAsString(docstring=True, show_ver=False)