implement proposal for fetching paths and retaining structure of dirs and packages (#914)

* implement proposal

* update docs and replace py-env

* more docs

* suggested proposal

* update docs

* add to_file parameter

* remove comment from Makefile

* suggested improvements

* move tests from basic to py_config

* retain leading slash from the first path

pyscriptjs/src/plugins/fetch.ts

@@ -0,0 +1,39 @@
+import { joinPaths } from '../utils';
+import { FetchConfig } from "../pyconfig";
+
+export function calculatePaths(fetch_cfg: FetchConfig[]) {
+    const fetchPaths: string[] = [];
+    const paths: string[] = [];
+    fetch_cfg.forEach(function (each_fetch_cfg: FetchConfig) {
+        const from = each_fetch_cfg.from || "";
+        const to_folder = each_fetch_cfg.to_folder || ".";
+        const to_file = each_fetch_cfg.to_file;
+        const files = each_fetch_cfg.files;
+        if (files !== undefined)
+        {
+            if (to_file !== undefined)
+            {
+                throw Error(`Cannot use 'to_file' and 'files' parameters together!`);
+            }
+            for (const each_f of files)
+            {
+                const each_fetch_path = joinPaths([from, each_f]);
+                fetchPaths.push(each_fetch_path);
+                const each_path = joinPaths([to_folder, each_f]);
+                paths.push(each_path);
+            }
+        }
+        else
+        {
+            fetchPaths.push(from);
+            const filename = to_file || from.split('/').pop();
+            if (filename === '') {
+                throw Error(`Couldn't determine the filename from the path ${from}, supply ${to_file} parameter!`);
+            }
+            else {
+                paths.push(joinPaths([to_folder, filename]));
+            }
+        }
+    });
+    return [paths, fetchPaths];
+}