Allow multiple symlink destinations

aitf relies on the behavior

example/aitf-data-for-run

@@ -53,11 +53,11 @@ def parse_args():
         metavar='DATE',
         help='scan time ancillary data is needed for')
 
-    ap.add_argument('destination', type=arg_directory,
+    ap.add_argument('destination', type=arg_directory, nargs='+',
         metavar='FINAL_PATH',
-        help='write required files here, possibly as symbolic links')
+        help='write symbolic links to required files here (actual files may be placed in the first destination provided)')
 
-    add_cache_dir_arg(ap)
+    add_cache_dir_arg(ap, '--cache')
 
     ap.add_argument('--cache-only', action='store_true',
         help='do not download; only use files already in cache')
@@ -89,10 +89,10 @@ def main():
     aitf.conlog.setup_logging()
     args = parse_args()
 
-    cache_dir = args.dir
+    cache_dir = args.cache
     if not os.access(cache_dir, os.W_OK):
-        logging.warning(f'I do not appear to be able to have write access to "{cache_dir}". Downloading directly into {args.destination}')
-        args.dir = args.destination
+        logging.warning(f'I do not appear to be able to have write access to "{cache_dir}". Downloading directly into {args.destination[0]}')
+        args.cache = args.destination[0]
 
     do_download = not args.cache_only
 
@@ -100,29 +100,30 @@ def main():
 
         logging.progress("Acquiring SST")
         sststats = aitf.ancil.SST.DownloadStatistics()
-        sst_files = aitf.ancil.SST.download_for_time(args.scan_time, args.dir, do_download = do_download, download_stats = sststats)
+        sst_files = aitf.ancil.SST.download_for_time(args.scan_time, args.cache, do_download = do_download, download_stats = sststats)
         log_download_report("SST Download Summary", sststats)
 
             # using SST instead of GFS to show that 
             # DownloadStatistics are interchangable.
         logging.progress("Acquiring GFS")
         gfsstats = aitf.ancil.SST.DownloadStatistics()
-        gfs_files = aitf.ancil.GFS.download_for_time(args.scan_time, args.dir, do_download = do_download, download_stats = sststats)
+        gfs_files = aitf.ancil.GFS.download_for_time(args.scan_time, args.cache, do_download = do_download, download_stats = sststats)
         log_download_report("GFS Download Summary", gfsstats)
 
         log_download_report("Total Download Summary", sststats + gfsstats)
 
         logging.progress("Symbolically linking into place")
         all_files = list(sst_files) + list(gfs_files)
-        for file in all_files:
-            f = os.path.relpath(file, args.dir)
-            src = os.path.join(args.dir, f)
-            dst = hack_oisst_preliminary_filename(os.path.join(args.destination, f))
-            dst_dir = os.path.dirname(dst)
-            os.makedirs(dst_dir, exist_ok=True)
-            logging.info(src + ' -> ' + dst)
-            if src != dst:
-                os.symlink(src, dst)
+        for destination in args.destination:
+            for file in all_files:
+                f = os.path.relpath(file, args.cache)
+                src = os.path.join(args.cache, f)
+                dst = hack_oisst_preliminary_filename(os.path.join(destination, f))
+                dst_dir = os.path.dirname(dst)
+                os.makedirs(dst_dir, exist_ok=True)
+                logging.info(src + ' -> ' + dst)
+                if src != dst: # src==dst if we set args.cache to args.destination[0]
+                    os.symlink(src, dst)
 
     except csppfetch.DownloadsFailedException as e:
         logging.fatal(str(e))