#' @title Export a \link[SingleCellExperiment]{SingleCellExperiment} R object as
 #' Python annData object

 #' @description Writes all assays, colData, rowData, reducedDims, and altExps objects in a
 #' \link[SingleCellExperiment]{SingleCellExperiment} to a Python annData object in the .h5ad format
 #' All parameters of Anndata.write_h5ad function (https://icb-anndata.readthedocs-hosted.com/en/stable/anndata.AnnData.write_h5ad.html)
 #' are available as parameters to this export function and set to defaults. Defaults can be
 #' overridden at function call.
 #' @param sce \link[SingleCellExperiment]{SingleCellExperiment} R object to be
 #'  exported.
 #' @param useAssay Character. The name of assay of
 #' interests that will be set as the primary matrix of the output AnnData.

 #' Default \code{"counts"}.

 #' @param outputDir Path to the directory where .h5ad outputs will be written. Default is the current working directory.
 #' @param prefix Prefix to use for the name of the output file. Default \code{"sample"}.
 #' @param overwrite Boolean. Default \code{TRUE}.
 #' @param compression If output file compression is required, this variable accepts

 #' 'gzip', 'lzf' or "None" as inputs. Default \code{"gzip"}.

 #' @param compressionOpts Integer. Sets the compression level
 #' @param forceDense Default \code{False} Write sparse data as a dense matrix.

 #' Refer \code{anndata.write_h5ad} documentation for details. Default \code{NULL}.

 #' @return Generates a Python anndata object containing data from \code{inSCE}.

 #' @examples
 #' data(sce_chcl, package = "scds")

 #' \dontrun{

 #' exportSCEtoAnnData(sce=sce_chcl, compression="gzip")

 #' }

 #' @export

 exportSCEtoAnnData <- function(sce,

                                 useAssay = 'counts',
                                 outputDir = "./",
                                 prefix = "sample",
                                 overwrite = TRUE,

                                 compression = c('gzip','lzf', "None"),

                                 compressionOpts = NULL,

                                 forceDense = FALSE){

   compression <- match.arg(compression)

   #forceDense <- match.arg(forceDense)

   if (compression == 'None'){
     compression <- NULL
   }
   if (!reticulate::py_module_available(module = "scanpy")) {
     warning("Cannot find python module 'scanpy', please install Conda and",
             " run sctkPythonInstallConda() or run sctkPythonInstallVirtualEnv().",
             "If one of these have been previously run to install the modules,",
             "make sure to run selectSCTKConda() or selectSCTKVirtualEnvironment(),",
             " respectively, if R has been restarted since the module installation.",

             " Alternatively, 'scanpy' can be installed on the local machine",

             "with pip (e.g. pip install --user scanpy) and then the 'use_python()'",
             " function from the 'reticulate' package can be used to select the",
             " correct Python environment.")
     return(sce)}
   dir.create(outputDir, showWarnings = FALSE, recursive = TRUE)
   fileName <- paste0(prefix,".h5ad")
   filePath <- file.path(outputDir,fileName)
   if (file.exists(filePath) && !isTRUE(overwrite)) {
     stop(paste0(path, " already exists. Change 'outputDir' or set 'overwrite' to TRUE."))

   }
   if (isTRUE(forceDense)) {
     forceDense <- "True"
   } else if (isFALSE(forceDense)) {
     forceDense <- "False"
   } else {
     stop("Argument `forceDense` should be `TRUE` or `FALSE`")
   }
   AssayName <- SummarizedExperiment::assayNames(sce)
   for (assay in AssayName){
     if (!methods::is(SummarizedExperiment::assay(sce, assay), 'dgCMatrix')) {
       SummarizedExperiment::assay(sce, assay) <- .convertToMatrix(SummarizedExperiment::assay(sce, assay))

     }

   }
   annData <- .sce2adata(sce, useAssay)

   annData$write_h5ad(filePath,

                      compression = compression,

                      compression_opts = compressionOpts,
                      force_dense = forceDense)
 }