first pass at implementing tar_terra_rasts()

* For use with multiple raster files, which are saved as a `SpatRasterCollection` object
* Tests (surprisingly?) Pass
* Need to address some issues of how GDAL options are used/passed/manipulated
* 🚀 🚀 🚀

NAMESPACE

@@ -3,6 +3,7 @@
 export(geotargets_option_get)
 export(geotargets_option_set)
 export(tar_terra_rast)
+export(tar_terra_rasts)
 export(tar_terra_vect)
 importFrom(rlang,"%||%")
 importFrom(rlang,arg_match0)

R/tar-terra-rasts.R

@@ -0,0 +1,160 @@
+#' Create a terra _SpatRasterCollection_ target
+#'
+#' Provides a target format for [terra::SpatRasterCollection] objects,
+#'   which have no restriction in the extent or other geometric parameters.
+#'
+#' @param filetype character. File format expressed as GDAL driver names passed
+#'   to [terra::writeRaster()]
+#' @param gdal character. GDAL driver specific datasource creation options
+#'   passed to [terra::writeRaster()]
+#' @param ... Additional arguments not yet used
+#'
+#' @inheritParams targets::tar_target
+#' @seealso [targets::tar_target_raw()]
+#' @author Andrew Gene Brown
+#' @author Nicholas Tierney
+#' @export
+#' @examples
+#' if (Sys.getenv("TAR_LONG_EXAMPLES") == "true") {
+#'   targets::tar_dir({ # tar_dir() runs code from a temporary directory.
+#'     library(geotargets)
+#'     targets::tar_script({
+#'       elev_scale <- function(z = 1, projection = "EPSG:4326") {
+#'         terra::project(
+#'           terra::rast(system.file("ex", "elev.tif", package = "terra")) * z,
+#'           projection
+#'         )
+#'       }
+#'       list(
+#'         tar_terra_rasts(
+#'           raster_elevs,
+#'           # two rasters, one unaltered, one scaled by factor of 2 and
+#'           # reprojected to interrupted good homolosine
+#'           command = terra::sprc(list(
+#'             elev_scale(1),
+#'             elev_scale(2, "+proj=igh")
+#'           ))
+#'         )
+#'       )
+#'     })
+#'     targets::tar_make()
+#'     x <- targets::tar_read(raster_elevs)
+#'   })
+#' }
+tar_terra_rasts <- function(name,
+                           command,
+                           pattern = NULL,
+                           filetype = NULL,
+                           gdal = NULL,
+                           ...,
+                           tidy_eval = targets::tar_option_get("tidy_eval"),
+                           packages = targets::tar_option_get("packages"),
+                           library = targets::tar_option_get("library"),
+                           repository = targets::tar_option_get("repository"),
+                           iteration = targets::tar_option_get("iteration"),
+                           error = targets::tar_option_get("error"),
+                           memory = targets::tar_option_get("memory"),
+                           garbage_collection = targets::tar_option_get("garbage_collection"),
+                           deployment = targets::tar_option_get("deployment"),
+                           priority = targets::tar_option_get("priority"),
+                           resources = targets::tar_option_get("resources"),
+                           storage = targets::tar_option_get("storage"),
+                           retrieval = targets::tar_option_get("retrieval"),
+                           cue = targets::tar_option_get("cue")) {
+  check_pkg_installed("terra")
+
+  name <- targets::tar_deparse_language(substitute(name))
+
+  envir <- targets::tar_option_get("envir")
+
+  command <- targets::tar_tidy_eval(
+    expr = as.expression(substitute(command)),
+    envir = envir,
+    tidy_eval = tidy_eval
+  )
+
+  pattern <- targets::tar_tidy_eval(
+    expr = as.expression(substitute(pattern)),
+    envir = envir,
+    tidy_eval = tidy_eval
+  )
+
+  drv <- get_gdal_available_driver_list("raster")
+
+  # if not specified by user, pull the corresponding geotargets option
+  filetype <- filetype %||% geotargets_option_get("gdal.raster.driver")
+  filetype <- rlang::arg_match0(filetype, drv$name)
+
+  gdal <- gdal %||% geotargets_option_get("gdal.raster.creation_options")
+
+  targets::tar_target_raw(
+    name = name,
+    command = command,
+    pattern = pattern,
+    packages = packages,
+    library = library,
+    format = create_format_terra_rasters_sprc(filetype = filetype,
+                                              gdal = gdal,
+                                              ...),
+    repository = repository,
+    iteration = iteration,
+    error = error,
+    memory = memory,
+    garbage_collection = garbage_collection,
+    deployment = deployment,
+    priority = priority,
+    resources = resources,
+    storage = storage,
+    retrieval = retrieval,
+    cue = cue
+  )
+}
+
+#' @param filetype File format expressed as GDAL driver names passed to `terra::writeRaster()`
+#' @param gdal GDAL driver specific datasource creation options passed to `terra::writeRaster()`
+#' @param ... Additional arguments not yet used
+#' @noRd
+create_format_terra_rasters_sprc <- function(filetype, gdal, ...) {
+  check_pkg_installed("terra")
+
+  drv <- get_gdal_available_driver_list("raster")
+
+  filetype <- filetype %||% geotargets_option_get("gdal.raster.driver")
+  filetype <- rlang::arg_match0(filetype, drv$name)
+
+  gdal <- gdal %||% geotargets_option_get("gdal.raster.creation_options")
+  ## TODO
+  ## Need to append the "opt" argument for GDAL options that is currently
+  ## controlled with the if(i > 1) part.
+
+  .write_terra_rasters_sprc <- eval(
+    substitute(
+      function(object, path) {
+        for (i in seq(object)) {
+          if (i > 1) {
+            opt <- "APPEND_SUBDATASET=YES"
+          } else {
+            opt <- ""
+          }
+          terra::writeRaster(
+            x = object[i],
+            filename = path,
+            filetype = filetype,
+            overwrite = (i == 1),
+            gdal = opt
+          )
+        }
+      },
+      list(filetype = filetype, gdal = gdal)
+    )
+  )
+
+  format_sprc_geotiff <- targets::tar_format(
+    read = function(path) terra::sprc(path),
+    write = .write_terra_rasters_sprc,
+    marshal = function(object) terra::wrap(object),
+    unmarshal = function(object) terra::unwrap(object)
+  )
+
+  format_sprc_geotiff
+}