Fix file asset access issues on CRAN - DEM.tif excluded from package build

.Rbuildignore

@@ -11,7 +11,7 @@
 ^\.travis\.yml$
 ^\.github$
 ^WhiteboxTools_linux_amd64\.zip$
-^.*\.tif$
+^[^/]*\.tif$
 ^.*\.json$
 ^doc$
 ^Meta$

R/whitebox-package.R

@@ -96,16 +96,30 @@ sample_dem_data <- function(destfile = file.path(system.file('extdata', package=
         }
     }
     if (fp == "") {
-        try(download.file("https://github.com/opengeos/whiteboxR/raw/master/inst/extdata/DEM.tif",
-                          destfile = destfile,
-                          mode = "wb", ...))
+        # If file doesn't exist, try to download it
+        # First, determine the best location for the download
         if (missing(destfile)) {
-            fp <- system.file("extdata/DEM.tif", package = "whitebox")[1]
-        } else {
-            if (file.exists(destfile)) {
-                fp <- destfile
+            # Check if package installation directory is writable
+            pkg_extdata <- system.file('extdata', package="whitebox")
+            if (nzchar(pkg_extdata) && file.access(pkg_extdata, 2) == 0) {
+                # Package extdata is writable, use it
+                destfile <- file.path(pkg_extdata, 'DEM.tif')
+            } else {
+                # Package extdata is not writable (e.g., on CRAN), use temp directory
+                destfile <- file.path(tempdir(), 'whitebox_DEM.tif')
             }
         }
+
+        result <- try(download.file("https://github.com/opengeos/whiteboxR/raw/master/inst/extdata/DEM.tif",
+                          destfile = destfile,
+                          mode = "wb", ...), silent = TRUE)
+
+        if (!inherits(result, "try-error") && file.exists(destfile)) {
+            fp <- destfile
+        } else {
+            # Download failed, check one more time if file appeared in package directory
+            fp <- system.file("extdata/DEM.tif", package = "whitebox")[1]
+        }
     }
     fp
 }

tests/testthat/test-wbt_source.R

@@ -3,6 +3,7 @@ test_that("wbt_source (raster) works", {
     skip_if_not_installed("terra")
 
     f <- sample_dem_data()
+    skip_if(f == "")
 
     # raster source from geotiff path
     src <- wbt_source(f)
@@ -60,6 +61,7 @@ test_that("wbt_source (vector) works", {
     skip_if_not_installed("terra")
 
     f <- sample_soils_data()
+    skip_if(f == "")
 
     # vector source from shapefile
     src <- wbt_source(f)